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Sample records for cd sn te

  1. Effects of Sn-doping on morphology and optical properties of CdTe polycrystalline films

    Institute of Scientific and Technical Information of China (English)

    Li Jin; Yang Linyu; Jian Jikang; Zou Hua; Sun Yanfei

    2009-01-01

    Sn-doped CdTe polycrystalline films were successfully deposited on ITO glass substrates by close space sublimation. The effects of Sn-doping on the microstructure, surface morphology, and optical properties of polycrystalline films were studied using X-ray diffraction, scanning electron microscopy, and ultraviolet-visible spectrophotometry, respectively. The results show that the lower molar ratio of Sn and CdTe conduces to a strongly preferential orientation of (111) in films and a larger grain size, which indicates that the crystallinity of films can be improved by appropriate Sn-doping. As the molar ratio of Sn and CdTe increases, the preferential orientation of (111) in films becomes weaker, the grain size becomes smaller, and the crystal boundary becomes indistinct, which indicates that the crystallization growth of films is incomplete. However, as the Sn content increases, optical absorption becomes stronger in the visible region. In summary, a strongly preferential orientation of (111) in films and a larger grain size can be obtained by appropriate Sn-doping (molar ratio of Sn : CdTe = 0.06 : 1), while the film retains a relatively high optical absorption in the visible region. However, Sn-doping has no obvious influence on the energy gap of CdTe films.

  2. The Effect of High-Resistance SnO2 on CdS/CdTe Device Performance

    Energy Technology Data Exchange (ETDEWEB)

    Li, W.; Ribelin, R.; Mahathongdy, Y.; Albin, D.; Dhere, R.; Rose, D.; Asher, S.; Moutinho, H.; Sheldon, P.

    1998-10-06

    In this paper, we have studied the effect of high-resistance SnO2 buffer layers, deposited by low-pressure chemical-vapor deposition, on CdS/CdTe device performance. Our results indicate that when CdS/CdTe devices have a very thin layer of CdS or no CdS at all, the i-SnO2 buffer layer helps to increase device efficiency. When the CdS layer is thicker than 600{angstrom}, the device performance is dominated by CdS thickness, not the i-SnO2 layer. If a very thin CdS layer is to be used to enhance device performance, we conclude that a better SnO2 buffer layer is needed.

  3. Quantum spin Hall effect in α -Sn /CdTe(001 ) quantum-well structures

    Science.gov (United States)

    Küfner, Sebastian; Matthes, Lars; Bechstedt, Friedhelm

    2016-01-01

    The electronic and topological properties of heterovalent and heterocrystalline α -Sn/CdTe(001) quantum wells (QWs) are studied in dependence on the thickness of α -Sn by means of ab initio calculations. We calculate the topological Z2 invariants of the respective bulk crystals, which identify α -Sn as strong three-dimensional (3D) topological insulators (TIs), whereas CdTe is a trivial insulator. We predict the existence of two-dimensional (2D) topological interface states between both materials and show that a topological phase transition from a trivial insulating phase into the quantum spin Hall (QSH) phase in the QW structures occurs at much higher thicknesses than in the HgTe case. The QSH effect is characterized by the localization, dispersion, and spin polarization of the topological interface states. We address the distinction of the 3D and 2D TI characters of the studied QW structures, which is inevitable for an understanding of the underlying quantum state of matter. The 3D TI nature is characterized by two-dimensional topological interface states, while the 2D phase exhibits one-dimensional edge states. The two different state characteristics are often intermixed in the discussion of the topology of 2D QW structures, especially, the comparison of ab initio calculations and experimental transport studies.

  4. Thin film growth of a topological crystal insulator SnTe on the CdTe (111) surface by molecular beam epitaxy

    Science.gov (United States)

    Ishikawa, Ryo; Yamaguchi, Tomonari; Ohtaki, Yusuke; Akiyama, Ryota; Kuroda, Shinji

    2016-11-01

    We report molecular beam epitaxial growth of a SnTe (111) layer on a CdTe template, fabricated by depositing it on a GaAs (111)A substrate, instead of BaF2 which has been conventionally used as a substrate. By optimizing temperatures for the growth of both SnTe and CdTe layers and the SnTe growth rate, we could obtain SnTe layers of the single phase grown only in the (111) orientation and of much improved surface morphology from the viewpoint of the extension and the flatness of flat regions, compared to the layers grown on BaF2. In this optimal growth condition, we have also achieved a low hole density of the order of 1017 cm-3 at 4 K, the lowest value ever reported for SnTe thin films without additional doping. In the magnetoresistance measurement on this optimized SnTe layer, we observe characteristic negative magneto-conductance which is attributed to the weak antilocalization effect of the two-dimensional transport in the topological surface state.

  5. Ultrahigh sensitivity and gain white light photodetector based on GaTe/Sn:CdS nanoflake/nanowire heterostructures.

    Science.gov (United States)

    Zhou, Weichang; Zhou, Yong; Peng, Yuehua; Zhang, Yong; Yin, Yanling; Tang, Dongsheng

    2014-11-01

    Optoelectronic diode based on PN heterostructure is one of the most fundamental device building blocks with extensive applications. Here we reported the fabrication and optoelectronic properties of GaTe/Sn : CdS nanoflake/nanowire PN heterojunction photodetectors. With high quality contacts between metal electrodes and Sn : CdS or GaTe, the electrical measurement of GaTe/Sn : CdS hybrid heterojunction under dark condition demonstrates an excellent diode characteristic with well-defined current rectification behavior. The photocurrent increases drastically under LED white light as well as red, green, UV illumination. The on-off ratio of current is about 100 for forward bias and 3000 for reverse bias, which clearly indicates the ultrahigh sensitivity of the heterostructure photodetector to white light. The responsivity and optical gain are determined to be 607 A W(-1) and (1.06-2.16) × 10(5)%, which is higher than previous reports of single GaTe or CdS nanostructures. Combination the Ids-Vds curves under different illumination power with energy band diagrams, we assign that both the light modulation effect under forward and reverse bias and the surface molecular oxygen adsorption/desorption mechanism are dominant to the electrical transport behavior of GaTe/Sn : CdS heterojunction. This heterostructure photodetector also shows good stability and fast response speed. Both the high photosensibility and fast response time described in the present study suggest strongly that the GaTe/Sn : CdS hybrid heterostructure is a promising candidate for photodetection, optical sensing and switching devices.

  6. Sn-doped CdTe as promising intermediate-band photovoltaic material

    Science.gov (United States)

    Flores, Mauricio A.; Menéndez-Proupin, Eduardo; Orellana, Walter; Peña, Juan L.

    2017-01-01

    The formation energies, charge transition levels and quasiparticle defect states of several tin-related impurities are investigated within the DFT  +  GW formalism. The optical spectrum obtained from the solution of the Bethe-Salpeter equation shows that the absorption strongly increases in the sub-bandgap region after doping, suggesting a two-step photoexcitation process that facilitates transitions from photons with insufficient energy to cause direct transitions from the valence to the conduction band via an intermediate-band. We propose Sn-doped CdTe as a promising candidate for the development of high-efficiency solar cells, which could potentially overcome the Shockley-Queisser limit.

  7. A comparative study of (ZnO, In{sub 2}O{sub 3}: SnO{sub 2}, SnO{sub 2})/CdS/CdTe/(Cu/)Ni heterojunctions

    Energy Technology Data Exchange (ETDEWEB)

    Vatavu, Sergiu, E-mail: svatavu@usm.md [Faculty of Physics and Engineering, Moldova State University, 60 A. Mateevici str., MD-2009 Chisinau, Republic of Moldova (Moldova, Republic of); Rotaru, Corneliu; Fedorov, Vladimir [Faculty of Physics and Engineering, Moldova State University, 60 A. Mateevici str., MD-2009 Chisinau, Republic of Moldova (Moldova, Republic of); Stein, Timo A. [Institut für Heterogene Materialsysteme, Helmholtz-Zentrum Berlin für Materialien und Energie, Lise-Meitner-Campus, Hahn-Meitner-Platz 1, 14109 Berlin (Germany); Caraman, Mihail; Evtodiev, Igor [Faculty of Physics and Engineering, Moldova State University, 60 A. Mateevici str., MD-2009 Chisinau, Republic of Moldova (Moldova, Republic of); Kelch, Carola; Kirsch, Michael [Institut für Heterogene Materialsysteme, Helmholtz-Zentrum Berlin für Materialien und Energie, Lise-Meitner-Campus, Hahn-Meitner-Platz 1, 14109 Berlin (Germany); Chetruş, Petru; Gaşin, Petru [Faculty of Physics and Engineering, Moldova State University, 60 A. Mateevici str., MD-2009 Chisinau, Republic of Moldova (Moldova, Republic of); Lux-Steiner, Martha Ch. [Institut für Heterogene Materialsysteme, Helmholtz-Zentrum Berlin für Materialien und Energie, Lise-Meitner-Campus, Hahn-Meitner-Platz 1, 14109 Berlin (Germany); Rusu, Marin [Faculty of Physics and Engineering, Moldova State University, 60 A. Mateevici str., MD-2009 Chisinau, Republic of Moldova (Moldova, Republic of); Institut für Heterogene Materialsysteme, Helmholtz-Zentrum Berlin für Materialien und Energie, Lise-Meitner-Campus, Hahn-Meitner-Platz 1, 14109 Berlin (Germany)

    2013-05-01

    The influence of the manufacturing technology on the structural properties of CdTe and CdS layers, components of the CdS/CdTe solar cells, has been investigated. CdTe based solar cells have been prepared using glass substrates coated with different transparent conductive oxides (TCOs: SnO{sub 2}, In{sub 2}O{sub 3}: SnO{sub 2} (ITO), ZnO:Al, ZnO:Al/i-ZnO). The analysis of the technology combined with various investigation methods allowed to determine optimum deposition parameters for CdS and CdTe for each type of TCO used. X-ray diffraction (XRD) and grazing incidence XRD analysis have been carried out for TCO, CdS, and CdTe layers at different deposition stages before and after annealing in the presence of CdCl{sub 2} in air. The reflection spectra in the 100–600 cm{sup −1} spectral region have been thoroughly studied by using Fourier transform infrared spectroscopy. It was found that (i) the best quality possess CdS and CdTe thin films sequentially deposited on ZnO:Al substrates and that (ii) the pre-treatment defects can be effectively cured and most of the secondary phases can be removed by annealing, while the basic structure of the investigated thin films does not essentially change. - Highlights: ► Deposition technology of CdS and CdTe thin films. ► Slightly improved CdS film quality obtained for deposition on ZnO:Al substrates. ► Improved quality of CdTe deposited on CdS layers grown at high substrate temperature. ► Defects and secondary phases removal as a result of thermal annealing.

  8. Synthesis, transport properties, and electronic structure of Cu{sub 2}CdSnTe{sub 4}

    Energy Technology Data Exchange (ETDEWEB)

    Dong, Yongkwan; Khabibullin, Artem R.; Wei, Kaya; Ge, Zhen-Hua; Woods, Lilia M., E-mail: lmwoods@usf.edu; Nolas, George S., E-mail: gnolas@usf.edu [Department of Physics, University of South Florida, Tampa, Florida 33620 (United States); Martin, Joshua [Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States); Salvador, James R. [Chemical and Materials Systems Laboratory, GM R and D Center, Warren, Michigan 48090 (United States)

    2014-06-23

    A new stannite phase was synthesized and its temperature dependent transport properties were investigated. Cu{sub 2}CdSnTe{sub 4} possesses strong p-type conduction, while the temperature dependence of the thermal conductivity exhibits typical dielectric behavior. Electronic structure calculations allowed for a description of the transport characteristics in terms the energy band structure, density of states, and Fermi surface. The potential for thermoelectric applications is also discussed.

  9. Interface Study of ITO/ZnO and ITO/SnO2 Complex Transparent Conductive Layers and Their Effect on CdTe Solar Cells

    Directory of Open Access Journals (Sweden)

    Tingliang Liu

    2013-01-01

    Full Text Available Transparent ITO/ZnO and ITO/SnO2 complex conductive layers were prepared by DC- and RF-magnetron sputtering. Their structure and optical and electronic performances were studied by XRD, UV/Vis Spectroscopy, and four-probe technology. The interface characteristic and band offset of the ITO/ZnO, ITO/SnO2, and ITO/CdS were investigated by Ultraviolet Photoelectron Spectroscopy (UPS and X-ray Photoelectron Spectroscopy (XPS, and the energy band diagrams have also been determined. The results show that ITO/ZnO and ITO/SnO2 films have good optical and electrical properties. The energy barrier those at the interface of ITO/ZnO and ITO/SnO2 layers are almost 0.4 and 0.44 eV, which are lower than in ITO/CdS heterojunctions (0.9 eV, which is beneficial for the transfer and collection of electrons in CdTe solar cells and reduces the minority carrier recombination at the interface, compared to CdS/ITO. The effects of their use in CdTe solar cells were studied by AMPS-1D software simulation using experiment values obtained from ZnO, ITO, and SnO2. From the simulation, we confirmed the increase of Eff, FF, Voc, and Isc by the introduction of ITO/ZnO and ITO/SnO2 layers in CdTe solar cells.

  10. Measurement of cross sections producing short-lived nuclei by 14MeV neutron. Cd, Sn, Te, Nd, Gd, Re

    Energy Technology Data Exchange (ETDEWEB)

    Sakane, H.; Yamamoto, H.; Kawade, K. [Nagoya Univ. (Japan); Iida, T.; Takahashi, A.

    1998-03-01

    Nine neutron activation cross sections producing the nuclei with half-lives between 25sec and 22min were measured at energy range between 13.4 and 14.9 MeV by activation method. The (n,p) and (n,{alpha}) reaction cross sections were measured for the isotopes of {sup 110}Cd, {sup 112}Sn, {sup 122}Te, {sup 130}Te and {sup 185}Re and those of {sup 130}Te, {sup 148}Nd and {sup 158}Gd, respectively. The present results were compared with our systematics proposed on the basis of 58 cross section data of (n,p) and 33 data of (n,{alpha}) reaction. Good agreements have been seen between them. (author)

  11. Novel CdTe Cell Fabrication Process with Potential for Low Cost and High Throughput

    Energy Technology Data Exchange (ETDEWEB)

    Wu, X.; Sheldon, P.

    2000-01-01

    There are several production disadvantages inherent in the conventional SnO(2)/CdS/CdTe manufacturing processes. In this paper, we report a novel manufacturing process for fabrication of polycrystalline Cd(2)SnO(4)/Zn(2)/SnO(4)/CdS/CdTe thin-film solar cells that yielded a CdS/CdTe device with an NREL-confirmed efficiency of 14.0%.

  12. Studies of key technologies for CdTe solar modules

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    In this paper, CdS thin films, which act as the window layer and n-type partner to the p-type CdTe layer, were prepared by chemical bath deposition (CBD). CdTe thin films were deposited by the close-spaced sublimation (CSS) method. To obtain high-quality back contacts, a Te-rich layer was created with chemical etching and back contact materials were applied after CdTe annealing. The results indicate that the ZnTe/ZnTe:Cu complex layers show superior performance over other back contacts. Finally, by using laser scribing and mechanical scribing, the CdTe mini-modules were fabricated, in which a glass/SnO2:F/CdS/CdTe/ZnTe/ZnTe:Cu/Ni solar module with a PWQC-confirmed total-area efficiency of 7.03% (54 cm2) was achieved.

  13. HgTe-CdTe SUPERLATTICES

    OpenAIRE

    Smith, D; Mcgill, T.

    1984-01-01

    We report on a theoretical study of the electronic properties of HgTe-CdTe superlattices. The band gap as a function of layer thickness, effective masses normal to the layer plane and tunneling length are compared to the corresponding (Hg, Cd)Te alloys. We find that the superlattice possesses a number of properties that may make it superior to the corresponding alloy as an infrared material.

  14. Topological crystalline insulator SnTe nanoribbons

    Science.gov (United States)

    Dahal, Bishnu R.; Dulal, Rajendra P.; Pegg, Ian L.; Philip, John

    2017-03-01

    Topological crystalline insulators are systems in which a band inversion that is protected by crystalline mirror symmetry gives rise to nontrivial topological surface states. SnTe is a topological crystalline insulator. It exhibits p-type conductivity due to Sn vacancies and Te antisites, which leads to high carrier density in the bulk. Thus growth of high quality SnTe is a prerequisite for understanding the topological crystalline insulating behavior. We have grown SnTe nanoribbons using a solution method. The width of the SnTe ribbons varies from 500 nm to 2 μm. They exhibit rock salt crystal structure with a lattice parameter of 6.32 Å. The solution method that we have adapted uses low temperature, so the Sn vacancies can be controlled. The solution grown SnTe nanoribbons exhibit strong semiconducting behavior with an activation energy of 240 meV. This activation energy matches with the calculated band gap for SnTe with a lattice parameter of 6.32 Å, which is higher than that reported for bulk SnTe. The higher activation energy makes the thermal excitation of bulk charges very difficult on the surface. As a result, the topological surfaces will be free from the disturbance caused by the thermal excitations

  15. Investigation of Junction Properties of CdS/CdTe Solar Cells and their Correlation to Device Properties (Presentation)

    Energy Technology Data Exchange (ETDEWEB)

    Dhere, R. G.; Zhang, Y.; Romero, M. J.; Asher, S. E.; Young, M.; To, B.; Noufi, R.; Gessert, T. A.

    2008-05-01

    The objective of the Junction Studies are: (1) understand the nature of the junction in the CdTe/CdS device; (2) correlate the device fabrication parameters to the junction formation; and (3) develop a self consistent device model to explain the device properties. Detailed analysis of CdS/CdTe and SnO{sub 2}/CdTe devices prepared using CSS CdTe is discussed.

  16. Comparison Between Research-Grade SnO2 and Commercial Available SnO2 for Thin-Film CdTe Solar Cell (Poster)

    Energy Technology Data Exchange (ETDEWEB)

    Li, X.; Pankow, J.; To, B.; Gessert, T.

    2008-05-01

    A comparison between research-grade, tin-oxide (SnO{sub 2}) thin films and those available from commercial sources is performed. The research-grade SnO{sub 2} film is fabricated at NREL by low-pressure metal-organic chemical vapor deposition. The commercial SnO{sub 2} films are Pilkington Tec 8 and Tec 15 fabricated by atmospheric-pressure chemical vapor deposition. Optical, structural, and compositional analyses are performed. From the optical analysis, an estimation of the current losses due to the SnO{sub 2} layer and glass is provided. Our analysis indicates that the optical properties of commercial SnO{sub 2} could be improved for PV usage.

  17. Numerical Analysis of Novel Back Surface Field for High Efficiency Ultrathin CdTe Solar Cells

    OpenAIRE

    Matin, M.A.; Tomal, M. U.; A. M. Robin; N. Amin

    2013-01-01

    This paper numerically explores the possibility of high efficiency, ultrathin, and stable CdTe cells with different back surface field (BSF) using well accepted simulator AMPS-1D (analysis of microelectronics and photonic structures). A modified structure of CdTe based PV cell SnO2/Zn2SnO4/CdS/CdTe/BSF/BC has been proposed over reference structure SnO2/Zn2SnO4/CdS/CdTe/Cu. Both higher bandgap materials like ZnTe and Cu2Te and low bandgap materials like As2Te3 and Sb2Te3 have been used as BSF ...

  18. Stripe structure CdTe-CdZnTe-CdTe in a bulk single crystal

    Science.gov (United States)

    Azoulay, M.; Sinvani, M.; Mizrachi, M.; Feldstein, H.

    1994-03-01

    In this paper we present a study that was aimed at performing a selective diffusion of Zn into CdTe. A single crystal CdTe wafer fabricated into a "tooth-like" structure which was further subjected to high temperature annealing in the presence of Zn vapour. The sample was then cut parallel to the diffusion direction and a Zn concentration analysis, using an electron microprobe, was performed. As expected, the stripe structure CdTe-CdZnTe-CdTe has been confirmed. The Zn decay profiles were fitted to a modified diffusion model, suggesting a bulk diffusion mechanism coupled with a surface reaction. Practical implementation of this stripe structure for an infrared light waveguide is being evaluated.

  19. Interface reactions in CdTe solar cell processing

    Energy Technology Data Exchange (ETDEWEB)

    Albin, D.; Dhere, R.; Swartzlander-Guest, A. [National Renewable Energy Lab., Golden, CO (United States)] [and others

    1998-12-31

    Currently, the best performing CdS/CdTe solar cells use a superstrate structure in which CdTe is deposited on a heated CdS/SnO{sub 2}/Glass substrate. In the close-spaced-sublimation (CSS) process, substrate temperatures in the range 550 C to 620 C are common. Understanding how these high processing temperatures impact reactions at the CdS/CdTe interface in addition to reactions between previously deposited layers is critical. At the SnO{sub 2}/CdS interface the authors have determined that SnO{sub 2} can be susceptible to reduction, particularly in H{sub 2} ambients. Room-temperature sputtered SnO{sub 2} shows the most susceptibility. In contrast, higher growth temperature chemical vapor deposited (CVD) SnO{sub 2} appears to be much more stable. Elimination of unstable SnO{sub 2} layers, and the substitution of thermal treatments for H{sub 2} anneals has produced total-area solar conversion efficiencies of 13.6% using non-optimized SnO{sub 2} substrates and chemical-bath deposited (CBD) CdS. Alloying and interdiffusion at the CdS/CdTe interface was studied using a new lift-off approach which allows enhanced compositional and structural analysis at the interface. Small-grained CdS, grown by a low-temperature CBD process, results in more CdTe{sub 1{minus}x}S{sub x} alloying (x = 12--13%) relative to larger-grained CdS grown by high-temperature CSS (x{approximately}2--3%). Interdiffusion of S and Te at the interface, measured with lift-off samples, appears to be inversely proportional to the amount of oxygen used during the CSS CdTe deposition. The highest efficiency to date using CSS-grown CdS is 10.7% and was accomplished by eliminating oxygen during the CdTe deposition.

  20. Large area thin film CdTe and Zn(x)Cd(1-x)Te heterojunction solar cells

    Science.gov (United States)

    Chu, T. L.; Chu, S. S.; Firszt, F.; Naseem, H. A.; Stawski, R.

    Thin film CdTe heterojunction solar cells have been prepared by the deposition of p-type CdTe films on CdS/SnO2:F/glass substrates using chemical vapor deposition (CVD) and close-spaced sublimation (CSS) techniques. The relative merits of the two techniques are discussed, and the characteristics of solar cells prepared by CVD and CSS techniques are compared. In addition, the properties of Zn(x)Cd(1-x)Te have been investigated.

  1. An analysis of point defects induced by In, Al, Ni, and Sn dopants in Bridgman-grown CdZnTe detectors and their influence on trapping of charge carriers

    Science.gov (United States)

    Gul, R.; Roy, U. N.; James, R. B.

    2017-03-01

    In this research, we studied point defects induced in Bridgman-grown CdZnTe detectors doped with Indium (In), Aluminium (Al), Nickel (Ni), and Tin (Sn). Point defects associated with different dopants were observed, and these defects were analyzed in detail for their contributions to electron/hole (e/h) trapping. We also explored the correlations between the nature and abundance of the point defects with their influence on the resistivity, electron mobility-lifetime (μτe) product, and electron trapping time. We used current-deep level transient spectroscopy to determine the energy, capture cross-section, and concentration of each trap. Furthermore, we used the data to determine the trapping and de-trapping times for the charge carriers. In In-doped CdZnTe detectors, uncompensated Cd vacancies (VCd-) were identified as a dominant trap. The VCd- were almost compensated in detectors doped with Al, Ni, and Sn, in addition to co-doping with In. Dominant traps related to the dopant were found at Ev + 0.36 eV and Ev + 1.1 eV, Ec + 76 meV and Ev + 0.61 eV, Ev + 36 meV and Ev + 0.86 eV, Ev + 0.52 eV and Ec + 0.83 eV in CZT:In, CZT:In + Al, CZT:In + Ni, and CZT:In + Sn, respectively. Results indicate that the addition of other dopants with In affects the type, nature, concentration (Nt), and capture cross-section (σ) and hence trapping (tt) and de-trapping (tdt) times. The dopant-induced traps, their corresponding concentrations, and charge capture cross-section play an important role in the performance of radiation detectors, especially for devices that rely solely on electron transport.

  2. Carrier dynamics and activation energy of CdTe/ZnTe nanostructures with different CdTe thicknesses

    Science.gov (United States)

    Han, Won Il; Lee, Ju Hyung; Choi, Jin Chul; Lee, Hong Seok

    2013-05-01

    We investigate the dimensional transition and optical properties of CdTe/ZnTe nanostructures with various CdTe thicknesses. The excitonic peak corresponding to the transitions from the ground electronic sub-band to the ground heavy-hole band in CdTe/ZnTe nanostructures shows different redshifts with increasing CdTe thickness due to variations in the dimensions of CdTe/ZnTe nanostructures. Time-resolved photoluminescence (PL) measurements used to study the carrier dynamics show that the decay time of 4.0 monolayer (ML) CdTe/ZnTe nanostructures is longer than that of CdTe/ZnTe nanostructures with different CdTe thicknesses. The activation energy of electrons confined in 4.0 ML CdTe/ZnTe nanostructures, as obtained from the temperature-dependent PL spectra, is higher than that of electrons confined in CdTe/ZnTe nanostructures with different CdTe thicknesses. These results indicate that the carrier dynamics and activation energy of CdTe/ZnTe nanostructures are affected by the thickness and dimensions of CdTe/ZnTe nanostructures.

  3. 125Te NMR chemical-shift trends in PbTe-GeTe and PbTe-SnTe alloys.

    Science.gov (United States)

    Njegic, B; Levin, E M; Schmidt-Rohr, K

    2013-01-01

    Complex tellurides, such as doped PbTe, GeTe, and their alloys, are among the best thermoelectric materials. Knowledge of the change in (125)Te NMR chemical shift due to bonding to dopant or "solute" atoms is useful for determination of phase composition, peak assignment, and analysis of local bonding. We have measured the (125)Te NMR chemical shifts in PbTe-based alloys, Pb1-xGexTe and Pb1-xSnxTe, which have a rocksalt-like structure, and analyzed their trends. For low x, several peaks are resolved in the 22-kHz MAS (125)Te NMR spectra. A simple linear trend in chemical shifts with the number of Pb neighbors is observed. No evidence of a proposed ferroelectric displacement of Ge atoms in a cubic PbTe matrix is detected at low Ge concentrations. The observed chemical shift trends are compared with the results of DFT calculations, which confirm the linear dependence on the composition of the first-neighbor shell. The data enable determination of the composition of various phases in multiphase telluride materials. They also provide estimates of the (125)Te chemical shifts of GeTe and SnTe (+970 and +400±150 ppm, respectively, from PbTe), which are otherwise difficult to access due to Knight shifts of many hundreds of ppm in neat GeTe and SnTe.

  4. Study of the CdS/CdTe interface and its relevance to solar cell properties

    Science.gov (United States)

    Dhere, Ramesh Gurupad

    CdTe based devices have shown significant progress over the last decade. CdS/CdTe devices fabricated by close-spaced sublimation have resulted in 15.8% efficiency. To understand the effect of CdS/CdTe interface properties on device properties, a detailed investigation of the dependence of properties of CdS, CdTe and CdS/CdTe interface on various processing parameters is reported. Analysis of CdS/CdTe devices fabricated under identical conditions, was carried out to determine any correlation between the interface properties and device characteristics. Possible mechanisms to explain the correlation are presented. The CdS layers were deposited by chemical bath deposition (CBD) on glass/SnOsb2 substrates. The CdTe layers were grown by close-spaced sublimation (CSS) on glass/SnOsb2/CdS substrates. Post-deposition CdClsb2 heat-treatment was carried out using different concentrations of CdClsb2/methanol solution. CBD CdS gives conformal coverage on rough SnOsb2 layers at a thickness as low as 30 nm. Under optimal conditions, CdS films with refractive index close to bulk index are obtained indicating that the layers are void-free. The grain-size of CBD CdS films is independent of film thickness and is established during the early part of growth. AFM analysis of CSS CdTe shows that the films are faceted for the entire temperature range (475sp°C-625sp°C) investigated, the grain-size increases with substrate temperature, and the films are free of voids. X-ray diffraction analysis reveals that CdTe films grown at substrate temperatures ≥525sp°C have preferred orientation and the orientation is not affected by the CdClsb2 heat-treatment, indicating that the films deposited at these temperatures are more compact. TEM analysis of CdS/CdTe structures suggests that the majority of structural defects in the CdTe layers are generated at the interface and are caused by lattice mismatch and growth conditions. Cathodoluminescence and photoluminescence analysis shows that CdClsb2

  5. Degradation and capacitance: voltage hysteresis in CdTe devices

    Science.gov (United States)

    Albin, D. S.; Dhere, R. G.; Glynn, S. C.; del Cueto, J. A.; Metzger, W. K.

    2009-08-01

    CdS/CdTe photovoltaic solar cells were made on two different transparent conducting oxide (TCO) structures in order to identify differences in fabrication, performance, and reliability. In one set of cells, chemical vapor deposition (CVD) was used to deposit a bi-layer TCO on Corning 7059 borosilicate glass consisting of a F-doped, conductive tin-oxide (cSnO2) layer capped by an insulating (undoped), buffer (iSnO2) layer. In the other set, a more advanced bi-layer structure consisting of sputtered cadmium stannate (Cd2SnO4; CTO) as the conducting layer and zinc stannate (Zn2SnO4; ZTO) as the buffer layer was used. CTO/ZTO substrates yielded higher performance devices however performance uniformity was worse due to possible strain effects associated with TCO layer fabrication. Cells using the SnO2-based structure were only slightly lower in performance, but exhibited considerably greater performance uniformity. When subjected to accelerated lifetime testing (ALT) at 85 - 100 °C under 1-sun illumination and open-circuit bias, more degradation was observed in CdTe cells deposited on the CTO/ZTO substrates. Considerable C-V hysteresis, defined as the depletion width difference between reverse and forward direction scans, was observed in all Cu-doped CdTe cells. These same effects can also be observed in thin-film modules. Hysteresis was observed to increase with increasing stress and degradation. The mechanism for hysteresis is discussed in terms of both an ionic-drift model and one involving majority carrier emission in the space-charge region (SCR). The increased generation of hysteresis observed in CdTe cells deposited on CTO/ZTO substrates suggests potential decomposition of these latter oxides when subjected to stress testing.

  6. 具有高阻抗本征SnO2过渡层的CdS/CdTe多晶薄膜太阳电池%Polycrystalline CdS/CdTe thin-film Solar cells with intrinsic SnO2 films of high resistance

    Institute of Scientific and Technical Information of China (English)

    曾广根; 冯良桓; 郑家贵; 黎兵; 雷智; 武莉莉; 蔡亚平; 李卫; 张静全; 蔡伟

    2006-01-01

    采用超声喷雾热解法制备了具有高阻抗的本征SnO2透明导电膜,将其运用在CdS层减薄了的CdS/CdTe多晶薄膜太阳电池中,对减薄后的CdS薄膜进行了XRD,AFM图谱分析,并对电池进行了光、暗I-V,光谱响应和C-V测试.结果表明,在高阻膜上沉积的减薄CdS薄膜(111)取向更明显,但易形成微孔.引入高阻层后,能消除CdS微孔形成的微小漏电通道,有效保护p-n结,改善了电池的并联电阻、填充因子和短波响应,使载流子浓度增加,暗饱和电流密度减小,从而电池性能得到改善,电池转换效率增加了14.4%.

  7. Characterization of intermixing at the CdS/CdTe interface in CSS deposited CdTe

    Science.gov (United States)

    Dhere, R. G.; Asher, S. E.; Jones, K. M.; Al-Jassim, M. M.; Moutinho, H. R.; Rose, D. H.; Dippo, P.; Sheldon, P.

    1996-01-01

    CdS/CdTe structures deposited on different substrates are analyzed using transmission electron microscopy (TEM), secondary ion mass spectrometry (SIMS), optical transmission, atomic force microscopy (AFM), X-ray diffraction (XRD) and photoluminescence (PL). The microstructure of CdTe was found to be independent of CdS crystallinity, and the structural defects at CdS/CdTe interface are generated principally by the lattice mismatch between CdS and CdTe. The interdiffusion at the CdS/CdTe interface was found to be a function of substrate temperature and CdCl2 heat treatment.

  8. Comparison Between Research-Grade and Commercially Available SnO2 for Thin-Film CdTe Solar Cells: Preprint

    Energy Technology Data Exchange (ETDEWEB)

    Li, X.; Pankow, J.; To, B.; Gessert, T.

    2008-05-01

    Compared to commercial SnO2 (with similar film thickness and sheet resistance), research-grade SnO2 has higher optical transmittance and higher electron mobility. Based on our study, changing the glass substrate and improving the SnO2 quality could improve the optical properties of commercial SnO2.

  9. ALE-CdS/CdTe-PV-cells

    Energy Technology Data Exchange (ETDEWEB)

    Skarp, J.; Anttila, E.; Rautiainen, A.; Suntola, T. (Microchemistry Ltd., Espoo (Finland))

    1992-01-01

    Atomic Layer Epitaxy, ALE, has been applied to grow CdS/CdTe-thin film solar cells. ALE offers the possibility of growing both CdS and CdTe in a single process and tailoring the interface of CdS and CdTe. The thickness of CdS was varied and the optimum was found to be in the range of 50-100 nm with good heterojunction performance and CdTe-crystallinity leading to excellent photovoltaic properties. The structures with thinner CdS layers suffered low open circuit voltage but on the other hand with thicker CdS the short circuit current was limited by the absorption of CdS. (author)

  10. Numerical Analysis of Novel Back Surface Field for High Efficiency Ultrathin CdTe Solar Cells

    Directory of Open Access Journals (Sweden)

    M. A. Matin

    2013-01-01

    Full Text Available This paper numerically explores the possibility of high efficiency, ultrathin, and stable CdTe cells with different back surface field (BSF using well accepted simulator AMPS-1D (analysis of microelectronics and photonic structures. A modified structure of CdTe based PV cell SnO2/Zn2SnO4/CdS/CdTe/BSF/BC has been proposed over reference structure SnO2/Zn2SnO4/CdS/CdTe/Cu. Both higher bandgap materials like ZnTe and Cu2Te and low bandgap materials like As2Te3 and Sb2Te3 have been used as BSF to reduce minority carrier recombination loss at the back contact in ultra-thin CdTe cells. In this analysis the highest conversion efficiency of CdTe based PV cell without BSF has been found to be around 17% using CdTe absorber thickness of 5 μm. However, the proposed structures with different BSF have shown acceptable efficiencies with an ultra-thin CdTe absorber of only 0.6 μm. The proposed structure with As2Te3 BSF showed the highest conversion efficiency of 20.8% ( V,  mA/cm2, and . Moreover, the proposed structures have shown improved stability in most extents, as it was found that the cells have relatively lower negative temperature coefficient. However, the cell with ZnTe BSF has shown better overall stability than other proposed cells with temperature coefficient (TC of −0.3%/°C.

  11. S and Te inter-diffusion in CdTe/CdS hetero junction

    Energy Technology Data Exchange (ETDEWEB)

    Enriquez, J. Pantoja [Cuerpo Academico-Energia y Sustentabilidad, Universidad Politecnica de Chiapas, Eduardo J. Selvas S/N, Col. Magisterial, Tuxtla Gutierrez 29010, Chiapas (Mexico); Gomez Barojas, E. [CIDS-ICUAP, Apdo. Postal 1651, 72000 Puebla (Mexico); Silva Gonzalez, R.; Pal, U. [Instituto de Fisica, Benemerita Universidad Autonoma de Puebla, Puebla (Mexico)

    2007-09-22

    Effects of post formation thermal annealing of the CdTe-CdS device on the inter-diffusion of S and Te at the junction in a substrate configuration device have been studied by Auger electron spectroscopy. While the migration of S and Te atoms increases with annealing temperature, the extent of S diffusion is always higher than the diffusion of Te atoms. Inter-diffusion of S and Te causes the formation of CdTe{sub 1-x}S{sub x} ternary compound at the CdTe-CdS interface. (author)

  12. Time-Resolved Photoluminescence Spectroscopy Evaluation of CdTe and CdTe/CdS Quantum Dots

    OpenAIRE

    Yuan, Zhimin; Yang, Ping; Cao, Yongqiang

    2012-01-01

    CdTe and CdTe/CdS quantum dots (QDs) were prepared in aqueous solutions using thioglycolic acid as a stabilizing agent. The photoluminescence (PL) wavelength of the QDs depended strongly on the size of CdTe cores and the thickness of CdS shells. Being kept at room temperature for 130 days, the PL wavelength of CdTe and CdTe/CdS QDs was red-shifted. However the red-shifted degree of CdTe QDs is larger than that of CdTe/CdS QDs. The size of CdTe QDs and the thickness of CdS play important roles...

  13. Numerical modeling of CdS/CdTe and CdS/CdTe/ZnTe solar cells as a function of CdTe thickness

    Energy Technology Data Exchange (ETDEWEB)

    Amin, Nowshad [Department of Electrical, Electronic and System Engineering, Faculty of Engineering, National University of Malaysia (UKM), Bangi 43600, Selangor D.E (Malaysia); Sopian, Kamaruzzaman [Solar Energy Research Institute, National University of Malaysia (UKM), Bangi 43600, Selangor D.E (Malaysia); Konagai, Makoto [Department of Electrical and Electronic Engineering, Tokyo Institute of Technology, 2-12-1 O-okayama, Meguro-ku, Tokyo 152-8552 (Japan)

    2007-08-15

    CdTe-based solar cells have long been of interest for terrestrial usage because of their high potential conversion efficiency (in the range of 18-24%) with low-cost manufacturability and concern over environmental effects. In order to conserve material and address environmental pollution concerns as well as to reduce carrier recombination loss throughout the absorber layer, efforts have been carried out to decrease the thickness of the CdTe absorption layer to 1 {mu}m. As a result, to date, the experimental part of this study has realized cell efficiencies of 15.3% and 11.5% with 7 and 1.2-{mu}m-thick CdTe layers, grown by close-spaced sublimation (CSS) [N. Amin, T. Isaka, T. Okamoto, A. Yamada, M. Konagai, Jpn. J. Appl. Phys. 38 (8) (1999) 4666; N. Amin, T. Isaka, A. Yamada, M. Konagai, Sol. Energy Matter. Sol. Cells 67 (2001) 195]. Since some problems remain with such thin 1 {mu}m CdTe layers, possible methods to realize higher efficiency have been investigated using novel solar cell structures, with the help of numerical analyses tools. In the theory part of this study, numerical analysis with a 1-D simulation program named NSSP (Numerical Solar Cell Simulation Program) has been used to simulate these structures. We investigated the viability of CdTe thickness reduction to 1 {mu}m together with the insertion of higher band-gap materials (i.e., ZnTe) at the back contacts to reduce carrier recombination loss there. The study shows potential results of the thickness reduction of CdTe absorption layer for a conventional CdS/CdTe/Cu-doped C structure with around 16% efficiency for cells below 3 {mu}m CdTe. Decreases were found in spectral response that suggest from minority carrier recombination loss at the back contact interface. A higher band-gap material like ZnTe has been inserted to produce a back surface field (BSF) to inhibit the minority carrier loss at the back contact. An increase in the efficiency to about 20% has been found for a 1 {mu}m-thin CdTe cell

  14. Pathways toward higher performance CdS/CdTe devices: Te exposure of CdTe surface before ZnTe:Cu/Ti contacting

    Energy Technology Data Exchange (ETDEWEB)

    Gessert, T.A., E-mail: tim.gessert@nrel.gov; Burst, J.M.; Wei, S.-H.; Ma, J.; Kuciauskas, D.; Rance, W.L.; Barnes, T.M.; Duenow, J.N.; Reese, M.O.; Li, J.V.; Young, M.R.; Dippo, P.

    2013-05-01

    Many studies of thin-film CdS/CdTe photovoltaic devices have suggested that performance may be improved by reducing recombination due to Te-vacancy (V{sub Te}), Te antisite (Te{sub Cd}), or Te-interstitial (Te{sub i}) defects. Although formation of these intrinsic defects is likely influenced by CdTe deposition parameters, it may be also coupled to the formation of beneficial cadmium vacancy (V{sub Cd}) defects. In this study, we expose the CdTe surface to Te vapor prior to ZnTe:Cu/Ti contact-interface formation with the goal of reducing V{sub Te} without significantly reducing V{sub Cd}. Initial results show that when this modified contact is used on a CdCl{sub 2}-treated CdS/CdTe device, poorer device performance results. This suggests two things: First, the amount of free-Te available during contact formation (either from chemical etching or Cu{sub x}Te or ZnTe deposition) may be a more important parameter to device performance than previously appreciated. Second, if processes have been used to reduce the effect of V{sub Te} (e.g., oxygen and chlorine additions), adding even a small amount of Te may produce detrimental defects. - Highlights: ► Te exposure of CdS/CdTe back contact reduces device performance. ► Field strength and minority carrier lifetime reduced. ► Calculations suggest formation of Te on Cd antisite defect.

  15. Tin oxide stability effects—their identification, dependence on processing and impacts on CdTe/CdS solar cell performance

    Science.gov (United States)

    Albin, Dave; Rose, Doug; Dhere, Ramesh; Niles, Dave; Swartzlander, Amy; Mason, Alice; Levi, Dean; Moutinho, Helio; Sheldon, Peter

    1997-02-01

    High efficiency polycrystalline thin film CdTe solar cells involve the growth of CdTe films on CdS/SnO2/glass substrates. The CdS layer in such a structure is commonly reported to benefit from a brief hydrogen anneal prior to the deposition of the CdTe film. In this paper, we show that the SnO2 layer can be susceptible to reduction in H2 and that the degree of susceptibility is dependent on the type of SnO2 used. Chemical vapor deposited (CVD) SnO2/glass substrates (Solarex Corp.) show the most resistance to reduction while room-temperature sputtered SnO2 films show the least resistance. When annealed under reducing conditions, Sn from the SnO2 reacts with S-containing impurities and oxygen in as-grown chemical bath deposited (CBD) CdS films to form SnS. Cd-containing impurities are more volatile resulting in a loss of Cd relative to S in films annealed in H2. These films appear dark due to the presence of SnS, a grayish-black impurity, in the CdS and possibly SnO in the SnO2. In normal CSS CdTe deposition processes where H2 annealing is followed by further heating to deposition temperatures in either He or He:O2 ambient, S loss occurs at temperatures exceeding the H2 anneal. If oxygen is absent, CdS films undergo loss of both Sn and S due to evaporation of the SnS. When O2 is present, SnS converts to SnO2 allowing for only the evaporation of sulfur. In this fashion, Sn levels on the CdS surface immediately prior to the deposition of CdTe, can be affected not only by the temperature of the H2 anneal, but also by the oxygen present during the CdTe deposition step. Modifications to the CdS/CdTe device fabrication process including the use of more stable tin oxide layers (CVD-grown) and lower temperature H2 anneals yield devices with higher open circuit voltage, fill-factors, and total-area efficiencies. Room-temperature sputtered tin oxide can be strengthened against reduction by annealing at 550 °C in 400 torr O2 prior to the CdS deposition step.

  16. Effects of CdTe growth conditions and techniques on the efficiency limiting defects and mechanisms in CdTe solar cells

    Science.gov (United States)

    Rohatgi, A.; Chou, H. C.; Jokerst, N. M.; Thomas, E. W.; Ferekides, C.; Kamra, S.; Feng, Z. C.; Dugan, K. M.

    1996-01-01

    CdTe solar cells were fabricated by depositing CdTe films on CdS/SnO2/glass substrates using close-spaced sublimation (CSS) and metalorganic chemical vapor deposition (MOCVD). Te/Cd mole ratio was varied in the range of 0.02 to 6 in the MOCVD growth ambient in an attempt to vary the native defect concentration. Polycrystalline CdTe layers grown by MOCVD and CSS both showed average grain size of about 2 μm. However, the CdTe films grown by CSS were found to be less faceted and more dense compared to the CdTe grown by MOCVD. CdTe growth techniques and conditions had a significant impact on the electrical characteristics of the cells. The CdTe solar cells grown by MOCVD in the Te-rich growth condition and by the CSS technique gave high cell efficiencies of 11.5% and 12.4%, respectively, compared to 6.6% efficient MOCVD cells grown in Cd-rich conditions. This large difference in efficiency is explained on the basis of (a) XRD measurements which showed a higher degree of atomic interdiffusion at the CdS/CdTe interface in high performance devices, (b) Raman measurements which endorsed more uniform and preferred grain orientation by revealing a sharp CdTe TO mode in the high efficiency cells, and (c) carrier transport mechanism which switched from tunneling/interface recombination to depletion region recombination in the high efficiency cells. In this study, Cu/Au layers were evaporated on CdTe for the back contact. Lower efficiency of the Te-rich MOCVD cells, compared to the CSS cells, was attributed to contact related additional loss mechanisms, such as Cd pile-up near Cu/CdTe interface which can give rise to Cd-vacancy defects in the bulk, and higher Cu concentration in the CdTe layer which can cause shunts in the device. Finally, SIMS measurements on the CdTe films of different crystallinity and grain size confirmed that grain boundaries are the main conduits for Cu migration into the CdTe film. Thus larger CdTe grain size or lower grain boundary area per unit volume

  17. Tin oxide stability effects{emdash}their identification, dependence on processing and impacts on CdTe/CdS solar cell performance

    Energy Technology Data Exchange (ETDEWEB)

    Albin, D.; Rose, D.; Dhere, R.; Niles, D.; Swartzlander, A.; Mason, A.; Levi, D.; Moutinho, H.; Sheldon, P. [National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, Colorado 80401 (United States)

    1997-02-01

    High efficiency polycrystalline thin film CdTe solar cells involve the growth of CdTe films on CdS/SnO{sub 2}/glass substrates. The CdS layer in such a structure is commonly reported to benefit from a brief hydrogen anneal prior to the deposition of the CdTe film. In this paper, we show that the SnO{sub 2} layer can be susceptible to reduction in H{sub 2} and that the degree of susceptibility is dependent on the type of SnO{sub 2} used. Chemical vapor deposited (CVD) SnO{sub 2}/glass substrates (Solarex Corp.) show the most resistance to reduction while room-temperature sputtered SnO{sub 2} films show the least resistance. When annealed under reducing conditions, Sn from the SnO{sub 2} reacts with S-containing impurities and oxygen in as-grown chemical bath deposited (CBD) CdS films to form SnS. Cd-containing impurities are more volatile resulting in a loss of Cd relative to S in films annealed in H{sub 2}. These films appear dark due to the presence of SnS, a grayish-black impurity, in the CdS and possibly SnO in the SnO{sub 2}. In normal CSS CdTe deposition processes where H{sub 2} annealing is followed by further heating to deposition temperatures in either He or He:O{sub 2} ambient, S loss occurs at temperatures exceeding the H{sub 2} anneal. If oxygen is absent, CdS films undergo loss of both Sn and S due to evaporation of the SnS. When O{sub 2} is present, SnS converts to SnO{sub 2} allowing for only the evaporation of sulfur. In this fashion, Sn levels on the CdS surface immediately prior to the deposition of CdTe, can be affected not only by the temperature of the H{sub 2} anneal, but also by the oxygen present during the CdTe deposition step. Modifications to the CdS/CdTe device fabrication process including the use of more stable tin oxide layers (CVD-grown) and lower temperature H{sub 2} anneals yield devices with higher open circuit voltage, fill-factors, and total-area efficiencies. (Abstract Truncated)

  18. Degradation and Capacitance-Voltage Hysteresis in CdTe Devices: Preprint

    Energy Technology Data Exchange (ETDEWEB)

    Albin, D. S.; Dhere, R. G.; Glynn, S. C.; DelCueto, J.; Metzger W. K.

    2009-07-01

    CdS/CdTe cells on CTO/ZTO TCO show greater intial performance than SnO2-gased substrates due to superior optical and electrical properties of the oxide layers and more rigorous CdCl2 processing. Performance unfiormity was a problem.

  19. New Architecture towards Ultrathin CdTe Solar Cells for High Conversion Efficiency

    Directory of Open Access Journals (Sweden)

    A. Teyou Ngoupo

    2015-01-01

    Full Text Available Solar Cell Capacitance Simulator in 1 Dimension (SCAPS-1D is used to investigate the possibility of realizing ultrathin CdTe based solar cells with high and stable conversion efficiency. In the first step, we modified the conventional cell structure by substituting the CdS window layer with a CdS:O film having a wide band gap ranging from 2.42 to 3.17 eV. Thereafter, we simulated the quantum efficiency, as well as the parameters of J-V characteristics, and showed how the thickness of CdS:O layer influences output parameters of Glass/SnO2/ZTO/CdS:O/CdTe1-xSx/CdTe/Ni reference cell. High conversion efficiency of 17.30% has been found using CdTe1-xSx (x=0.12 and CdTe layers of thickness 15 nm and 4 μm, respectively. Secondly, we introduced a BSR layer between the absorber layer and back metal contact, which led to Glass/SnO2/ZTO/CdS:O/CdTe1-xSx/CdTe/BSR/Ni configuration. We found that a few nanometers (about 5 nm of CdTe1-xSx layer is sufficient to obtain high conversion efficiency. For BSR layer, different materials with large band gap, such as ZnTe, Cu2Te, and p+-CdTe, have been used in order to reduce minority carrier recombination at the back contact. When ZnTe is used, high conversion efficiency of 21.65% and better stability are obtained, compared to other BSR.

  20. Dislocation reduction in HgCdTe grown on CdTe/Si

    Science.gov (United States)

    Wijewarnasuriya, Priyalal S.

    2016-05-01

    Bulk-grown CdZnTe (Zn = 3%) substrates are the natural choice for HgCdTe epitaxy since it is lattice matched to long wave LW-HgCdTe alloy. However, lack of large area CdZnTe substrates, high production costs, and more importantly, the difference in thermal expansion coefficients between CdZnTe and silicon Read out Integrated Circuits (ROIC) are some of the inherent drawbacks of CdZnTe substrates. Consequently, Hg1-xCdxTe detectors fabricated on silicon substrates are an attractive alternative. Recent developments in the molecular beam epitaxy (MBE) buffer layer growth technology on Si substrates has revolutionized the HgCdTe research and offered a new dimension to HgCdTe-based IR technology. Si substrates provide advantages in terms of relatively large area (3 to 6-inch diameter is easily obtained) compared to CZT substrate materials, durability during processing, and reliability to thermal cycling. Innovations in Si-based composite substrates made it possible to fabricate very large-format IR arrays that offer higher resolution, low-cost arrays and more dies per wafer. Between Si substrates and HgCdTe has large lattice mismatch of 19%. This leads to dislocation densities of low-107 cm-2 for optimal growth of HgCdTe on silicon-based substrates as compared to the mid-104 cm-2 dislocation density of HgCdTe grown on CdZnTe. This paper present dislocation reduction by two orders of magnitude using thermal cycle anneal under Hg environment on HgCdTe grown on Si substrates and as well as defect reduction in Cd(Se)Te buffer layers grown on Si Substrates.

  1. Device Fabrication using Crystalline CdTe and CdTe Ternary Alloys Grown by MBE

    Energy Technology Data Exchange (ETDEWEB)

    Zaunbrecher, Katherine; Burst, James; Seyedmohammadi, Shahram; Malik, Roger; Li, Jian V.; Gessert, Timothy A.; Barnes, Teresa

    2015-06-14

    We fabricated epitaxial CdTe:In/CdTe:As homojunction and CdZnTe/CdTe and CdMgTe/CdTe heterojunction devices grown on bulk CdTe substrates in order to study the fundamental device physics of CdTe solar cells. Selection of emitter-layer alloys was based on passivation studies using double heterostructures as well as band alignment. Initial results show significant device integration challenges, including low dopant activation, high resistivity substrates and the development of low-resistance contacts. To date, the highest open-circuit voltage is 715 mV in a CdZnTe/CdTe heterojunction following anneal, while the highest fill factor of 52% was attained in an annealed CdTe homojunction. In general, all currentvoltage measurements show high series resistance, capacitancevoltages measurements show variable doping, and quantum efficiency measurements show low collection. Ongoing work includes overcoming the high resistance in these devices and addressing other possible device limitations such as non-optimum junction depth, interface recombination, and reduced bulk lifetime due to structural defects.

  2. CdTe devices and method of manufacturing same

    Energy Technology Data Exchange (ETDEWEB)

    Gessert, Timothy A.; Noufi, Rommel; Dhere, Ramesh G.; Albin, David S.; Barnes, Teresa; Burst, James; Duenow, Joel N.; Reese, Matthew

    2015-09-29

    A method of producing polycrystalline CdTe materials and devices that incorporate the polycrystalline CdTe materials are provided. In particular, a method of producing polycrystalline p-doped CdTe thin films for use in CdTe solar cells in which the CdTe thin films possess enhanced acceptor densities and minority carrier lifetimes, resulting in enhanced efficiency of the solar cells containing the CdTe material are provided.

  3. n-(CdMgTe/CdTe)/(p-(CdTe/ZnCdTe/ZnTe)/p-GaAs heterostructure diode for photosensor applications

    Science.gov (United States)

    Yahia, I. S.; AlFaify, S.; Abutalib, M. M.; Chusnutdinow, S.; Wojtowicz, T.; Karczewski, G.; Yakuphanoglu, F.; Al-Bassam, A.; El-Naggar, A. M.; El-Bashir, S. M.

    2016-05-01

    High quality n-(CdMgTe:I/n-CdTe:I)/(p-CdTe:N/p-ZnCdTe:N/p-ZnTe:N)/p-GaAs heterojunction diodes have been fabricated by molecular beam epitaxial growth. The illumination effect on the complex impedance and conductivity of heterostructure diode was investigated. The illumination intensities were taken up to the 200 mW/cm2 with frequency range of 42 Hz to 1 MHz. The observed real and imaginary parts of the complex impedance were strongly dependent on the illumination frequency. The inverse relation was observed between the illumination intensity and the complex impedance. The relaxation mechanism of the diode was analyzed by the Cole-Cole plots. The radius of the Cole-Cole curve decreases with increasing illumination intensity. This suggests a mechanism of illumination dependent on the relaxation process. It is also found that the conductivity increases linearly with increasing the illumination intensity. We can conclude that the new design heterostructure diode in our work is a good candidate in photodetector and optoelectronic applications.

  4. (112)面CdTe/Cd1-yZnyTe,Hg1-xCdxTe/CdTe和CdTe/GaAs异质结的方向倾斜%Oriental Shift at CdTe/Cd1-yZnyTe, Hg1-xCdxTe/CdTe and CdTe/GaAs Heterojunctions Grown on (112) plane

    Institute of Scientific and Technical Information of China (English)

    刘义族; 于福聚

    2001-01-01

    用X射线双晶衍射(XDCD)法测得分子束外延(MBE)法生长的CdTe/Cd0.959Zn0.041Te(112)B异质结的倾斜角为0.2185°,而且朝[1-1-1]晶体学方向倾斜.为了获得较精确的倾斜角值,绘制了外延层和衬底衍射角的差值Δθ与绕样品表面法线旋转的角度φ之间的准正弦函数.为高分辨率透射电子显微镜(HRTEM)分析制备了MBE法生长的Hg0.535Cd0.465Te/CdTe/GaAs(1-12)B多层异质结的横截面薄膜. CdTe/GaAs异质结的HRTEM明场象表明CdTe(1-12)缓冲层相对于GaAs(1-12)衬底朝[1-1 1-]方向倾斜约3°,并且在Hg0.535Cd0.465Te/CdTe异质结,Hg0.535Cd0.465Te(1-12)外延膜相对于CdTe(1-12)缓冲层在[1 1-1]方向,即[1-1 1-]的反方向倾斜约1°.也分析了Hg0.535Cd0.465Te/CdTe/GaAs多层膜之间的倾斜角关系.

  5. Electrical properties of CdS/CdTe heterojunctions

    Science.gov (United States)

    Chu, T. L.; Chu, Shirley S.; Ang, S. T.

    1988-08-01

    The electrical properties of n-CdS/p-CdTe heterojunctions depend strongly on the cleanliness of the interface region. In this work, CdTe films were deposited on CdS/glass substrates by close-spaced sublimation (CSS) under various conditions. The dark current-voltage characteristics of the resulting heterojunctions were measured over a wide temperature range, and the capacitance-voltage characteristics were measured in the dark and under illumination. When the CdS surface is in situ cleaned prior to the deposition of the CdTe film, the current transport across the junction is controlled by a thermally activated process. Tunneling makes an important contribution to the interface recombination at temperatures below room temperature when the in situ cleaning of CdS is not used. The dark capacitance of CdS/CdTe heterojunctions prepared with in situ etching is essentially independent of the reverse bias due to intrinsic interface states. Under white light illumination, the 1/C 2 vs V relation is nearly linear. The CdS/CdTe heterojunctions without in situ cleaning showed different 1/C 2 vs V relations due to higher density of interface states. The in situ cleaning also has pronounced effects on the frequency dependence of dark and illuminated capacitances. Using the in situ cleaning technique, solar cells of about 1 cm2 area have achieved an AM 1.5 (global) efficiency of about 10.5%.

  6. Effects of Cd Interlayer on CdS/CdTe Thin Film Photovoltaics

    Science.gov (United States)

    Rivella, David; Cerqueira, Luis; Sahiner, M. Alper

    CdS/CdTe thin films are well known for their photovoltaic effects. However, it is also known that there are various factors that limit the output of the photovoltaic cells. In these particular thin films, a limiting factor is the interaction of CdS and the CdTe layers. By adding a Cd layer between CdS and CdTe, a buffer zone was created. Therefore, the interaction between the aforementioned layers was changed. In this study, the buffer zone was added to the photovoltaic cells, while the ratio of Cd to Te in the CdTe layer was varied, in order to observe the effects of the buffer in regards to the diffusion of Te in traditional CdTe/CdS photovoltaics. The samples were created on ITO coated glass using pulsed laser deposition. This created uniform samples with an approximate thickness of 0.75 microns. In order to test the effect of the Cd buffer layer, the CdTe layers were deposited with varying ratios of Cd to Te. XRD analysis confirmed that the deposited Cd and Te formed crystalline CdTe. The active carrier concentrations were then determined using Hall Effect measurements. The photovoltaic properties were measured using Keithley source meter set-up. The effect of structural modifications on the active carrier concentrations and photovoltaic properties will be discussed.

  7. Weak Topological Insulators in PbTe/SnTe superlattice

    Science.gov (United States)

    Yang, Gang; Liu, Junwei; Fu, Liang; Duan, Wenhui; Liu, Chaoxing

    2014-03-01

    It is desirable to realize topological phases in artificial structures by engineering electronic band structures. In this paper, we investigate (PbTe)m(SnTe)2n-m superlattices along the [001] direction and find a robust weak topological insulator phase for a large variety of layer numbers m and 2 n - m . We confirm this topologically non-trivial phase by calculating Z2 topological invariants and topological surface states based on the first-principles calculations. We show that the folding of Brillouin zone due to the superlattice structure plays an essential role in inducing topologically non-trivial phases in this system. This mechanism can be generalized to other systems in which band inversion occurs at multiple momenta, and gives us a brand-new way to engineer topological materials in artificial structures. We acknowledge support from the Ministry of Science and Technology of China and the National Natural Science Foundation of China. LF is supported by the DOE Office of Basic Energy Sciences.

  8. The analysis of CdS thin film at the processes of manufacturing CdS/CdTe solar cells

    Science.gov (United States)

    Chun, S.; Jung, Y.; Kim, J.; Kim, D.

    2011-07-01

    In sequence, the deposited CdS thin film had undergone physical and optical changes by the processes of manufacturing CdS/CdTe solar cells. CdS thin film was manufactured by the Chemical Bath Deposition (CBD) method. The aqueous solution was based on ammonia solution. The temperature of bath system was 75 °C and deposition time was 50 min. The thickness of deposited CdS thin film was about 200 nm. The substrate was the glass coated with SnO 2:F thin film. The following process was the deposition of CdTe thin film by the Closed-Space-Sublimation (CSS) method. The final process was the CdCl 2 heat treatment at N 2+O 2 atmosphere, and the contrast experiment progressed for CdCl 2-CdS thin film after CSS process at N 2 atmosphere. The phase transition of CdS thin film, stress relaxation and optical band gap narrowing were developed by each process. And so, the formation of cadmium oxide was detected after the CdCl 2 heat treatment. It influenced to increase the optical band gap of CdS thin film. The variation in the structure properties, optical properties and residual stresses of CdS thin film was analyzed by X-ray diffractometer (XRD), Raman spectroscopy and ultraviolet (UV)-visible (VIS) spectroscopy.

  9. Auger relative sensitivivity factors for CdTe oxide

    OpenAIRE

    P. Bartolo-Pérez; J. L. Peña; M.H. Farías

    1999-01-01

    The Auger lineshape of Te MNN in measurements of Auger spectra of CdTe oxide films with various degrees of oxidation was analyzed. By using standards from stoichiometric compounds, Auger relative sensitivity factors (RSF´s) of Cd, Te and O for CdTe oxide thin films were obtained. The value of the RFS of oxygen is about constant, 0.27-0.28, for the standard compound, CdO, TeO2 and CdTeO3 (considering the RSF of Cd as 1). However, the obtained RSF of Te changes from 0.69 in CdTe up to 0.87 in C...

  10. Development of optimal SnO{sub 2} contacts for CdTe photovoltaic applications. [Final technical report of Phase II

    Energy Technology Data Exchange (ETDEWEB)

    Xi, Jianping

    1999-09-16

    During this SBIR Phase II project, we have successfully established high quality SnO{sub 2}(F) based transparent conductive oxide coatings by atmospheric pressure chemical vapor deposition technique and built a large area prototype APCVD deposition system which incorporates innovative design features. This work enhances US photovoltaic research capability and other thin film oxide related research capability.

  11. CdS/CdTe Solar Cells Containing Directly Deposited CdSxTe1-x Alloy Layers: Preprint

    Energy Technology Data Exchange (ETDEWEB)

    Duenow, J. N.; Dhere, R. G.; Moutinho, H. R.; To, B.; Pankow, J. W.; Kuciauskas, D.; Gessert, T. A.

    2011-07-01

    A CdSxTe1-x layer forms by interdiffusion of CdS and CdTe during the fabrication of thin-film CdTe photovoltaic (PV) devices. The CdSxTe1-x layer is thought to be important because it relieves strain at the CdS/CdTe interface that would otherwise exist due to the 10% lattice mismatch between these two materials. Our previous work [1] has indicated that the electrical junction is located in this interdiffused CdSxTe1-x region. Further understanding, however, is essential to predict the role of this CdSxTe1-x layer in the operation of CdS/CdTe devices. In this study, CdSxTe1-x alloy films were deposited by radio-frequency (RF) magnetron sputtering and co-evaporation from CdTe and CdS sources. Both RF-magnetron-sputtered and co-evaporated CdSxTe1-x films of lower S content (x<0.3) have a cubic zincblende (ZB) structure akin to CdTe, whereas those of higher S content have a hexagonal wurtzite (WZ) structure like that of CdS. Films become less preferentially oriented as a result of a CdCl2 heat treatment (HT) at ~400 degrees C for 5 min. Films sputtered in a 1% O2/Ar ambient are amorphous as deposited, but show CdTe ZB, CdS WZ, and CdTe oxide phases after a CdCl2 HT. Films sputtered in O2 partial pressure have a much wider bandgap than expected. This may be explained by nanocrystalline size effects seen previously [2] for sputtered oxygenated CdS (CdS:O) films. Initial PV device results show that the introduction of a directly-deposited CdSxTe1-x alloy layer into the device structure produces devices of comparable performance to those without the alloy layer when a CdCl2 HT is performed. Further investigation is required to determine whether the CdCl2 heat treatment step can be altered or eliminated through direct deposition of the alloy layer.

  12. Analysis of CdS/CdTe devices incorporating a ZnTe:Cu/Ti Contact

    Energy Technology Data Exchange (ETDEWEB)

    Gessert, T.A. [National Renewable Energy Laboratory, 1617 Cole Blvd, Golden, Colorado 80401 (United States)]. E-mail: tim_gessert@nrel.gov; Asher, S. [National Renewable Energy Laboratory, 1617 Cole Blvd, Golden, Colorado 80401 (United States); Johnston, S. [National Renewable Energy Laboratory, 1617 Cole Blvd, Golden, Colorado 80401 (United States); Young, M. [National Renewable Energy Laboratory, 1617 Cole Blvd, Golden, Colorado 80401 (United States); Dippo, P. [National Renewable Energy Laboratory, 1617 Cole Blvd, Golden, Colorado 80401 (United States); Corwine, C. [National Renewable Energy Laboratory, 1617 Cole Blvd, Golden, Colorado 80401 (United States)

    2007-05-31

    High-performance CdS/CdTe photovoltaic devices can be produced using a ZnTe:Cu/Ti back contact deposited onto the CdTe layer. We observe that prolonged exposure of the ZnTe:Cu and Ti sputtering targets to an oxygen-containing plasma significantly reduces device open-circuit voltage and fill factor. High-resolution compositional analysis of these devices reveals that Cu concentration in the CdTe and CdS layers is lower for devices with poor performance. Capacitance-voltage analysis and related numerical simulations indicate that the net acceptor concentration in the CdTe is also lower for devices with poor performance. Photoluminescence analyses of the junction region reveal that the intensity of a luminescent peak associated with a defect complex involving interstitial Cu (Cu{sub i}) and oxygen on Te (O{sub Te}) is reduced in devices with poor performance. Combined with thermodynamic considerations, these results suggest that oxygen incorporation into the ZnTe:Cu sputtering target reduces the ability of sputtered ZnTe:Cu film to diffuse Cu into the CdTe.

  13. Quantized Nanocrystalline CdTe Thin Films

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Nanocrystalline CdTe thin films were prepared by asymmetric rectangular pulse electrodeposition in organic solution at 110°C. STM image shows a porous network morphology constructed by interconnected spherical CdTe crystallites with a mean diameter of 4.2 nm. A pronounced size quantization was indicated in the action and absorption spectra. Potentials dependence dual conductive behavior was revealed in the photocurrent-potential (I-V) curves.

  14. RF magnetron sputtering deposition of CdTe passivation on HgCdTe

    Science.gov (United States)

    Rutkowski, Jaroslaw; Adamiec, Krzysztof; Rogalski, Antoni

    1998-04-01

    In this study, we report the RF magnetron sputtering growth and characterization of CdTe passivant on bulk n-type HgCdTe. Our investigations include the HgCdTe surface preparation and in-situ pretreatment, deposition-induced surface damage, interface charge, CdTe film stoichiometry, and thermal stability. The metal-insulator-semiconductor test structures are processed and their electrical properties are measured by capacitance-voltage characteristics. The heterostructures are also characterized by reflectance measurement. In order to investigate the passivation properties of CdTe/HgCdTe heterostructures, we have modeled the band diagram of abrupt CdTe/HgCdTe heterojunction. The effect of sputtering growth condition parameters is also reported. The sputtering CdTe layers, exhibit excellent dielectric, insulating and mechano- chemical properties, as well as interface properties. The interfaces are characterized by slight accumulation and a small hysteresis. A carefully controlled growth process and surface pretreatment tailored to the specific material are required in order to obtain near flat band conditions on n- type materials. Additional informations on surface limitations are obtained from analyzing the I-V characteristics of photodiodes with metal gates covering the p-n junction surface location.

  15. Electrical and optical properties of magnetron sputtered Cd{sub 2}SnO{sub 4} transparent conducting oxide thin films for use in CdTe solar devices

    Energy Technology Data Exchange (ETDEWEB)

    Stoke, J.A., E-mail: jastoke2012@gmail.com [Rocky Mountain College, Billings, MT 59102 (United States); Beach, J.D.; Bradford, W.C.; Ohno, T.R. [Physics Department, Colorado School of Mines, Golden, CO 80102 (United States)

    2014-07-01

    In this study cadmium stannate Cd{sub 2}SnO{sub 4} (CTO), was sputtered onto borosilicate glass under substrate temperatures of ∼ 25 °C (room temp), 200 °C, 300 °C and 400 °C. The CTO films were then annealed in contact with cadmium sulfide (CdS). This annealing process consisted of placing the CTO samples face up in a thermal furnace with a separate piece of CdS film on a borosilicate substrate face down on top of the CTO sample. This arrangement was then heated to a temperature of 600 °C and annealed for one hour. The goal was to fabricate a CTO film with the highest transparency without sacrificing good electrical conductivity. The quality of CTO films, i.e. transparency and electrical conductivity can be greatly affected by processing conditions. In this paper the optical and electrical properties of CTO are investigated before and after thermal annealing to determine the affect of varying process conditions on the quality of the film. Spectroscopic ellipsometry analysis was performed on both as-deposited and annealed CTO to determine the nature of the optical response of the films over the spectral range of 0.73 to 3.34 eV. The electrical properties of the films were examined using both Hall effect data and optical Drude modeling of free carrier absorption. Structural properties of the films were determined from X-ray diffraction data. The result of this investigation is a high quality CTO film with a sheet resistance of ∼ 8 Ω/□. - Highlights: • Cadmium stannate (CTO) is characterized to achieve optimization as a transparent conducting oxide (TCO). • Spectroscopic ellipsometry results were substantiated with other measurements. • Specialized CTO processing yields a TCO film with low sheet resistance.

  16. IBIC analysis of CdTe/CdS solar cells

    CERN Document Server

    Colombo, E; Calusi, S; Giuntini, L; Giudice, A Lo; Manfredotti, C; Massi, M; Olivero, P; Romeo, A; Romeo, N; Vittone, E

    2016-01-01

    This paper reports on the investigation of the electronic properties of a thin film CdS/CdTe solar cell with the Ion Beam Induced Charge (IBIC) technique. The device under test is a thin film (total thickness around 10 um) multilayer heterojunction solar cell, displaying an efficiency of 14% under AM1.5 illumination conditions. The IBIC measurements were carried out using focused 3.150 MeV He ions raster scanned onto the surface of the back electrode. The charge collection efficiency (CCE) maps show inhomogeneous response of the cell to be attributed to the polycrystalline nature of the CdTe bulk material. Finally, the evolution of the IBIC signal vs. the ion fluence was studied in order to evaluate the radiation hardness of the CdS/CdTe solar cells in view of their use in solar modules for space applications.

  17. INVESTIGATION OF CdTe/CdS HETEROJUNCTION CHARACTERISTICS%CdTe/CdS异质结特性

    Institute of Scientific and Technical Information of China (English)

    郭江; 王万录; 刘高斌; 冯良桓

    2003-01-01

    从理论上对CdTe/CdS太阳电池CdS/CdTe异质结的特性进行了研究和讨论,结果表明可以简单利用改变CdTe、CdS两种半导体材料的掺杂浓度来改变CdS/CdTe异质结的能带结构.针对不同的能带结构采用了不同的物理模型,得到的CdS/CdTe异质结伏安特性曲线有一折点,且折点位置随异质结能带结构的变化而变化.

  18. ZnTe/CdTe thin-film heterojunctions

    Directory of Open Access Journals (Sweden)

    M.M. Kolesnyk

    2009-01-01

    Full Text Available In this work we have studied the structural and electrophysical properties of the ZnTe/CdTe heterojunctions, obtained by the method of thermal evaporation in quasi-closed volume. Investigations allowed to define the films structural parameters, such as texture, lattice constant, sizes of grains and coherent-scattering domains, micro-deformation level, and their dependence on the conditions of films production as well. Electrophysical investigations allowed to define the charge-transport mechanism in heterojunction.

  19. Syntheis and Photocurrent Performance of Graphene Oxide-CdTe/CdS Nanocomposite.

    Science.gov (United States)

    Ding, Liyun; Zhang, Bingyu; Li, Tao; Huang, Jun; Fan, Xiaochun

    2015-12-01

    Graphene with two-dimensional carbon nanostructures provides a potent strategy to enhance optoelectronic performance of semiconductor nanoparticles based light harvesting assemblies. Graphene oxide-CdTe/CdS (GO-CdTe/CdS) nanocomposites were successfully prepared by CdTe/CdS quantum dots (QDs) formed on the surface of graphene oxide sheets. The structure and optical properties of GO-CdTe/CdS nanocomposites were studied in detail. Photoluminescence measurements showed that the integration of CdTe/CdS QDs with graphene oxide significantly decreased its photoluminescence, which indicated effective transfer of photo-excited electrons from CdTe/CdS to graphene oxide. The generation of photocurrent on illumination of the GO-CdTe/CdS nanocomposite was studied. Significant enhancement in photocurrent induced by GO in CdTe/CdS QDs film had also been demonstrated due to increasing the charge separation and electron conduction.

  20. Synthesis and crystal structure of PdSnTe

    Energy Technology Data Exchange (ETDEWEB)

    Laufek, F. [Czech Geological Survey, Geologicka 6, 152 00 Praha 5 (Czech Republic)], E-mail: frantisek.laufek@geology.cz; Vymazalova, A. [Czech Geological Survey, Geologicka 6, 152 00 Praha 5 (Czech Republic); Navratil, J. [Joint Laboratory of Solid State Chemistry of IMC AS CR and University of Pardubice, Studentska 84, 532 10 Pardubice (Czech Republic); Drabek, M. [Czech Geological Survey, Geologicka 6, 152 00 Praha 5 (Czech Republic); Plasil, J. [Faculty of Science, Charles University, Albertov 6, 128 43 Praha 2 (Czech Republic); Plechacek, T. [Joint Laboratory of Solid State Chemistry of IMC AS CR and University of Pardubice, Studentska 84, 532 10 Pardubice (Czech Republic)

    2009-01-22

    The compound with composition PdSnTe was prepared by heating of stoichiometric amount of Pd, Sn and Te in silica glass tube at 400 deg. C. Its crystal structure was refined by Rietveld method using conventional X-ray powder diffraction data. PdSnTe shows orthorhombic symmetry, space group Pbca with unit cell parameters a = 6.5687(2), b = 6.6028(2), c = 12.8849(4) A, V = 558.8(1) A{sup 3} and Z = 8. The title compound can be viewed as a ternary-ordered variant of {alpha}-NiAs{sub 2}-type structure, it is isostructural with PtSiTe. Temperature dependence of electrical conductivity and Hall coefficient are presented, it suggests semimetallic or strongly degenerated semiconductor behaviour of the prepared compound.

  1. HgCdTe barrier infrared detectors

    Science.gov (United States)

    Kopytko, M.; Rogalski, A.

    2016-05-01

    In the last decade, new strategies to achieve high-operating temperature (HOT) detectors have been proposed, including barrier structures such as nBn devices, unipolar barrier photodiodes, and multistage (cascade) infrared detectors. The ability to tune the positions of the conduction and valence band edges independently in a broken-gap type-II superlattices is especially helpful in the design of unipolar barriers. This idea has been also implemented in HgCdTe ternary material system. However, the implementation of this detector structure in HgCdTe material system is not straightforward due to the existence of a valence band discontinuity (barrier) at the absorber-barrier interface. In this paper we present status of HgCdTe barrier detectors with emphasis on technological progress in fabrication of MOCVD-grown HgCdTe barrier detectors achieved recently at the Institute of Applied Physics, Military University of Technology. Their performance is comparable with state-of-the-art of HgCdTe photodiodes. From the perspective of device fabrication their important technological advantage results from less stringent surface passivation requirements and tolerance to threading dislocations.

  2. The formation of different phases of Cu {sub x}Te and their effects on CdTe/CdS solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, J. [National Renewable Energy Laboratory (NREL), Golden, CO 80401 (United States)]. E-mail: Jie_Zhou@nrel.gov; Wu, X. [National Renewable Energy Laboratory (NREL), Golden, CO 80401 (United States); Duda, A. [National Renewable Energy Laboratory (NREL), Golden, CO 80401 (United States); Teeter, G. [National Renewable Energy Laboratory (NREL), Golden, CO 80401 (United States); Demtsu, S.H. [Department of Physics, Colorado State University, Fort Collins, CO 80523 (United States)

    2007-06-25

    Material studies and device applications of Cu {sub x}Te in an NREL-developed CdTe solar cell structured as glass/Cd{sub 2}SnO{sub 4}/ZnSnO {sub x}/CdS/CdTe are presented. The Cu {sub x}Te primary back contact was formed by evaporating a Cu layer with various thicknesses at room temperature on HNO{sub 3}/H{sub 3}PO{sub 4} (NP) solution etched CdTe layer. A post-annealing was then followed. The structural evolution and electrical properties of Cu {sub x}Te were investigated. Cu/Te ratio and post-annealing temperature are two processing parameters in this study. The Cu {sub x}Te phases are mainly controlled by the Cu/Te ratio. After a post-annealing at a low temperature, such as 100 deg. C, no Cu {sub x}Te phase transformation from its as-deposited phase was observed. A post-annealing treatment at a higher temperature, such as 250 deg. C, can reveal the stoichiometric Cu {sub x}Te phases based on the Cu/Te ratio used in the devices. But a post-annealing at a further higher temperature, such as 400 deg. C, resulted in a complicated Cu {sub x}Te phase appearance. CuTe, Cu{sub 1.4}Te, and Cu{sub 2}Te are three major phases detected by X-ray diffraction (XRD) for different Cu thickness application annealed at 250 deg. C. Application of Cu thicker than 60 nm degrades open-circuit voltage (V {sub oc}) and shunting resistance (R {sub sh}), but increases series resistance (R {sub s}). The correlation between device performance and the Cu {sub x}Te back contact illustrates that the process used for forming the Cu{sub 2}Te back contact failed to produce good fill factor (FF) and also introduced higher barrier height. The best device was observed for a back contact with a mixed Cu{sub 1.4}Te and CuTe phases.

  3. 125Te NMR chemical-shift trends in PbTe–GeTe and PbTe–SnTe alloys

    Energy Technology Data Exchange (ETDEWEB)

    Njegic, Bosiljka [Ames Laboratory; Levin, Evgenii M. [Ames Laboratory; Schmidt-Rohr, Klaus [Ames Laboratory

    2013-10-08

    Complex tellurides, such as doped PbTe, GeTe, and their alloys, are among the best thermoelectric materials. Knowledge of the change in 125Te NMR chemical shift due to bonding to dopant or “solute” atoms is useful for determination of phase composition, peak assignment, and analysis of local bonding. We have measured the 125Te NMR chemical shifts in PbTe-based alloys, Pb1-xGexTe and Pb1-xSnxTe, which have a rocksalt-like structure, and analyzed their trends. For low x, several peaks are resolved in the 22-kHz MAS 125Te NMR spectra. A simple linear trend in chemical shifts with the number of Pb neighbors is observed. No evidence of a proposed ferroelectric displacement of Ge atoms in a cubic PbTe matrix is detected at low Ge concentrations. The observed chemical shift trends are compared with the results of DFT calculations, which confirm the linear dependence on the composition of the first-neighbor shell. The data enable determination of the composition of various phases in multiphase telluride materials. They also provide estimates of the 125Te chemical shifts of GeTe and SnTe (+970 and +400±150 ppm, respectively, from PbTe), which are otherwise difficult to access due to Knight shifts of many hundreds of ppm in neat GeTe and SnTe.

  4. Influence of CdTe thickness on structural and electrical properties of CdTe/CdS solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Salavei, A.; Rimmaudo, I. [Laboratory for Applied Physics, Department of Computer Science, University of Verona, Strada Le Grazie 15, 37134 Verona (Italy); Piccinelli, F. [Laboratorio di Chimica dello Stato Solido, DB, Univ. Verona, and INSTM, UdR Verona, Strada Le Grazie 15, 37134 Verona (Italy); Romeo, A., E-mail: alessandro.romeo@univr.it [Laboratory for Applied Physics, Department of Computer Science, University of Verona, Strada Le Grazie 15, 37134 Verona (Italy)

    2013-05-01

    Due to its high scalability and low production cost, CdTe solar cells have shown a very strong potential for large scale energy production. Although the number of modules produced could be limited by tellurium scarcity, it has been reported that reducing CdTe thickness down to 1.5 μm would solve this issue. There are, however, issues to be considered when reducing thickness, such as formation of pinholes, lower crystallization, and different possible effects on material diffusion within the interfaces. In this work, we present the study of CdTe solar cells fabricated by vacuum evaporation with different CdTe thicknesses. Several cells with a CdTe thickness ranging from 0.7 to 6 μm have been fabricated. The deposition process has been optimized accordingly and their physical and electrical properties have been studied. Thin cells show a different electrical behavior in terms of open circuit voltage and fill factor. Efficiencies range from 7% for thin CdTe cells to 13.5% for the standard thickness. - Highlights: ► Ultra thin CdTe absorbers have been prepared and studied. ► Grain size is depending on the CdTe thickness but spread in the grains increases. ► Lattice parameter is reduced only for ultra thin CdTe. ► The band gap reveals an intermixed CdTe absorber. ► The reason for lower efficiency of ultra thin CdTe is explained.

  5. Comparative study of CdS/CdTe cells fabricated with and without evaporated Te-layer

    Energy Technology Data Exchange (ETDEWEB)

    Potlog, T. [Physics Department, Moldova State University, 60, A. Mateevici str. Chisinau, MD-2009 (Moldova, Republic of)]. E-mail: tpotlog@usm.md; Ghimpu, L. [Physics Department, Moldova State University, 60, A. Mateevici str. Chisinau, MD-2009 (Moldova, Republic of); Antoniuc, C. [Physics Department, Moldova State University, 60, A. Mateevici str. Chisinau, MD-2009 (Moldova, Republic of)

    2007-05-31

    Thin film CdS/CdTe solar cells were fabricated by Close space Sublimation (CSS) at the Moldova State University using a Te layer at the back contact deposited by thermal evaporation. The influence of the Te layer thickness and a cadmium chloride solution treatment of the CdTe layer before and after Te layer deposition are studied. A proper comparison of the two CdS/CdTe solar cells shows that the cell with the Te layer has a higher current because of the higher blue photosensitivity, but has a lower open circuit voltage in relation to the absorber band gap.

  6. CdZnTe Background Measurement at Balloon Altitudes

    CERN Document Server

    Bloser, P F; Narita, T; Harrison, F

    1998-01-01

    We report results of an experiment conducted in May 1997 to measure CdZnTe background and background reduction schemes in space flight conditions similar to those of proposed hard X-ray astrophysics missions. A 1 cm^2 CdZnTe detector was placed adjacent to a thick BGO anticoincidence shield and flown piggybacked onto the EXITE2 scientific balloon payload. The planar shield was designed to veto background countsproduced by local gamma-ray production in passive material and neutron interactions in the detector. The CdZnTe and BGO were partially surrounded by a Pb-Sn-Cu shield to approximate the grammage of an X-ray collimator, although the field of view was still ~2 pi sr. At an altitude of 127000 feet we find a reduction in background by a factor of 6 at 100 keV. The non-vetoed background is 9 X 10^{-4} cts /cm^2-sec-keV at 100 keV, about a factor of 2 higher than that of the collimated (4.5 deg FWHM) EXITE2 phoswich detector. We compare our recorded spectrum with that expected from simulations using GEANT and...

  7. Band alignment at the interface of PbTe/SnTe heterojunction determined by X-ray photoelectron spectroscopy

    Science.gov (United States)

    Shu, Tianyu; Ye, Zhenyu; Lu, Pengqi; Chen, Lu; Xu, Gangyi; Zhou, Jie; Wu, Huizhen

    2016-11-01

    We report the determination of band alignment of PbTe/SnTe (111) heterojunction interfaces using X-ray photoelectron spectroscopy (XPS). Multiple core levels of Pb and Sn were utilized to determine the valence band offset (VBO) of the heterojunction. The XPS result shows a type-III band alignment with the VBO of 1.37+/- 0.18 \\text{eV} and the conduction band offset (CBO) of 1.23+/- 0.18 \\text{eV} . The experimental determination of the band alignment of the PbTe/SnTe heterojunction shall benefit the improvement of PbTe/SnTe-related optoelectronic and electronic devices.

  8. Adsorption properties of CdS-CdTe system semiconductors

    Science.gov (United States)

    Kirovskaya, I. A.; Nor, P. E.

    2013-12-01

    The adsorption of carbon(II) oxide and ammonia on nanofilms of solid solutions and binary compounds of the CdS-CdTe system is studied by means of piezoquartz microweighing, FTIR IR, and measuring electroconductivity. Allowing for the conditions and composition of semiconductor systems, we determine the mechanisms and principles of adsorption processes by analyzing the α p = f( T), α T = f( p), and α T = f( t) experimental dependences; IR spectra; the thermodynamic and kinetic characteristics of adsorption; the acid-base, electrophysical, and other characteristics of adsorbents; the electron nature of adsorbate molecules; and the obtained acid-base characteristics: the composition and adsorption characteristics and composition state diagrams. Previous statements on the nature and retention of local active centers responsible for adsorption and catalytic processes upon changes in their habitus and composition (as components of systems of the AIIIBV-AIIBVI and AIIBVI-AIIBVI types) on the surface of diamond-like semiconductors are confirmed. Specific features of the behavior of (CdS) x (CdTe)1 - x solid solutions are identified in addition to general features with binary compounds (CdS, CdTe), as is demonstrated by the presence of critical points on acid-base characteristics-composition and adsorption characteristics-composition diagrams. On the basis of these diagrams, the most active adsorbents (with respect to CO and NH3) used in designing highly sensitive and selective sensors are identified.

  9. MBE HgCdTe heterostructure detectors

    Science.gov (United States)

    Schulman, Joel N.; Wu, Owen K.

    1990-01-01

    HgCdTe has been the mainstay for medium (3 to 5 micron) and long (10 to 14 micron) wavelength infrared detectors in recent years. Conventional growth and processing techniques are continuing to improve the material. However, the additional ability to tailor composition and placement of doped layers on the tens of angstroms scale using molecular beam epitaxy (MBE) provides the opportunity for new device physics and concepts to be utilized. MBE-based device structures to be discussed here can be grouped into two categories: tailored conventional structures and quantum structures. The tailored conventional structures are improvements on familiar devices, but make use of the ability to create layers of varying composition, and thus band gap, at will. The heterostructure junction can be positioned independently of doping p-n junctions. This allows the small band gap region in which the absorption occurs to be separated from a larger band gap region in which the electric field is large and where unwanted tunneling can occur. Data from hybrid MBE/liquid phase epitaxy (LPE)/bulk structures are given. Quantum structures include the HgTe-CdTe superlattice, in which the band gap and transport can be controlled by alternating thin layers (tens of angstroms thick) of HgTe and CdTe. The superlattice has been shown to exhibit behavior which is non-alloy like, including very high hole mobilities, two-dimensional structure in the absorption coefficient, resonant tunneling, and anisotropic transport.

  10. CdTe and ZnTe metal interface formation and Fermi-level pinning

    Science.gov (United States)

    Wahi, A. K.; Carey, G. P.; Chiang, T. T.; Lindau, I.; Spicer, W. E.

    1989-01-01

    Interfacial morphology and Fermi-level pinning behavior at the interfaces of Al, Ag, and Pt with UHV-cleaved CdTe and ZnTe are studied using X-ray photoelectron and ultraviolet photoemission spectroscopies. Results are compared to metal/HgCdTe interface formation. For Al/CdTe, a case is found where significantly greater intermixing occurs in CdTe than seen on HgCdTe. The Al/ZnTe interface is also more abrupt than Al/CdTe. Band bending results for interfaces of all three metals with p-CdTe and p-ZnTe are presented and implications for metal/HgZnTe interface formation are considered.

  11. Structural reproducibility of CdTe thin films deposited on different substrates by close space sublimation method

    Energy Technology Data Exchange (ETDEWEB)

    Potlog, T.; Spalatu, N.; Maticiuc, N. [Physics Department, Moldova State University, Chisinau (Moldova); Hiie, J.; Valdna, V.; Mikli, V.; Mere, A. [Department of Materials Science, Tallinn University of Technology, Tallinn (Estonia)

    2012-02-15

    We report on the characterization of polycrystalline CdTe thin films grown directly on glass, SnO{sub 2}-coated glass, and CdS/SnO{sub 2}/glass at relatively low temperatures by employing the close space sublimation technique (CSS). The deposited films have been characterized by using optical absorption, X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray analysis (EDX). Based on the SEM and optical analysis, the CdTe/CdS/SnO{sub 2}/glass thin films exhibit a superior crystal quality and reproducibility in comparison to other CdTe films grown on glass and SnO{sub 2}/glass. XRD study reveals that films are polycrystalline with a cubic crystal structure. The EDX characterization indicates that all CdTe thin films are nearly stoichiometric. The optical absorption study shows a larger variation of band gap from 1.485 to 1.495 eV for CdTe grown on SnO{sub 2}-coated glass. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  12. High performance p-i-n CdTe and CdZnTe detectors

    CERN Document Server

    Khusainov, A K; Ilves, A G; Morozov, V F; Pustovoit, A K; Arlt, R D

    1999-01-01

    A breakthrough in the performance of p-i-n CdTe and CdZnTe detectors is reported. The detector stability has been significantly improved, allowing their use in precise gamma and XRF applications. Detectors with energy resolution close to Si and Ge were produced operating with only -30--35 deg. C cooling (by a Peltier cooler of 15x15x10 mm size and a consumed power less than 5 W). Presently detectors with volume of up to 300 mm sup 3 are available. In terms of photoelectric effect efficiency it corresponds to HPGe detectors with volumes of about 1.5 cm sup 3. The possibilities of further improvement of CdTe and CdZnTe detector characteristics are discussed in this paper.

  13. CdTe nanoparticles for the deposition of CdTe films using close spaced sublimation

    Science.gov (United States)

    Schumm, Benjamin; Althues, Holger; Kaskel, Stefan

    2010-08-01

    In this work a nanostructured CdTe powder was applied as a source material for CdTe film deposition via Close Spaced Sublimation (CSS). Growth kinetics and the resulting film properties were studied and compared to the films deposited from a commercially available CdTe bulk powder as source. The nanostructured powder was synthesized by a solvothermal elemental reaction of Cd and Te in ethylene diamine leading to particles of around 100-500 nm in diameter with a specific surface area of 4.1 m 2 g -1. An increase in the deposition rate by the factor of 1.7 was observed for the nanostructured powder as compared to the bulk material.

  14. Celdas solares de heteroestructura: contacto metálico/p-CdTe/n-CdS/n-TCO/vidrio

    OpenAIRE

    Márquez Marín, Joaquín

    2015-01-01

    En este trabajo se realizó la optimización de películas policristalinas con las características necesarias para la fabricación de heteroestructuras del tipo metal/CdTe/CdS/TCO/Vidrio para aplicaciones fotovoltaicas. Los óxidos conductores transparentes (TCO´s) usados como contacto frontal fueron películas de CdIn2O4, Cd2SnO4 e ITO comercial. Las películas de CdS fueron depositadas por el método de baño químico a 90 °C y las películas de CdTe fueron depositadas por la técnica de sublimación...

  15. CdTe Films Deposited by Closed-space Sublimation

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    CdTe films are prepared by closed-space sublimation technology. Dependence of film crystalline on substrate materials and substrate temperature is investigated. It is found that films exhibit higher crystallinity at substrate temperature higher than 400℃. And the CdTe films deposited on CdS films with higher crystallinity have bigger crystallite and higher uniformity. Treatment with CdCl2 methanol solution promotes the crystallite growth of CdTe films during annealing.

  16. Temperature dependent electroreflectance study of CdTe solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Raadik, T., E-mail: taavi.raadik@ttu.ee [Tallinn University of Technology, Ehitajate tee 5, 19086 Tallinn (Estonia); Krustok, J.; Josepson, R.; Hiie, J. [Tallinn University of Technology, Ehitajate tee 5, 19086 Tallinn (Estonia); Potlog, T.; Spalatu, N. [Moldova State University, A. Mateevici str. 60, MD-2009 Chisinau (Moldova, Republic of)

    2013-05-01

    Cadmium telluride is a promising material for large scale photovoltaic applications. In this paper we study CdS/CdTe heterojunction solar cells with electroreflectance spectroscopy. Both CdS and CdTe layers in solar cells were grown sequentially without intermediate processing by the close-space sublimation method. Electroreflectance measurements were performed in the temperature range of T = 100–300 K. Two solar cells were investigated with conversion efficiencies of 4.1% and 9.6%. The main focus in this work was to study the temperature dependent behavior of the broadening parameter and the bandgap energy of CdTe thin film in solar cells. Room temperature bandgap values of CdTe were E{sub g} = 1.499 eV and E{sub g} = 1.481 eV for higher and lower efficiency solar cells, respectively. Measured bandgap energies are lower than for single crystal CdTe. The formation of CdTe{sub 1−x}S{sub x} solid solution layer on the surface of CdTe is proposed as a possible cause of lower bandgap energies. - Highlights: ► Temperature dependent electroreflectance measurements of CdS/CdTe solar cells ► Investigation of junction properties between CdS and CdTe ► Formation of CdTe{sub 1−} {sub x}S{sub x} solid solution layer in the junction area.

  17. Electronic structure and band alignments of ZnTe/CrTe(0 0 1), CdSe/CrTe(0 0 1) and CdTe/CrTe(0 0 1) interfaces

    Indian Academy of Sciences (India)

    F Ahmadian; R Zare

    2011-08-01

    All-electron full potential calculations based on spin density functional theory were performed to study cubic zincblende (ZB) and hexagonal NiAs structures of bulk CrTe and ZnTe/CrTe(0 0 1), CdTe/CrTe(0 0 1) and CdSe/CrTe(0 0 1) interfaces. The lattice mismatch effect in ZB CrTe and magnetic properties of CrTe in the ideal ZB CrTe structure were investigated. The band alignment properties of the ZnTe/CrTe(0 0 1), CdTe/CrTe(0 0 1) and CdSe/CrTe(0 0 1) interfaces were computed and a rather large minority valence band offset of about 1.09 eV was observed in ZnTe/CrTe(0 0 1) heterojunction. Also in the CdTe/CrTe(0 0 1) and CdSe/CrTe(0 0 1) interfaces, the conduction band minimum of minority spin in CrTe was above the conduction band minimum of CdTe and CdSe and so the majority spin electrons could be directly injected to both semiconductors, indicating the possibility of highly efficient spin injection into the CdSe and CdTe semiconductors.

  18. CdTe and CdZnTe crystals for room temperature gamma-ray detectors

    CERN Document Server

    Franc, J; Belas, E; Grill, R; Hlidek, P; Moravec, P; Bok, J B

    1999-01-01

    CdTe(Cl) detectors from CdTe single crystals, grown by the Bridgman method from Te-rich melt, were fabricated. The quality of the detectors was tested with sup 5 sup 7 Co and sup 2 sup 4 sup 1 Am sources. In the sup 5 sup 7 Co spectrum low noise is demonstrated by the presence of a 14 keV peak and good resolution approx 7 keV (FWHM) evident from the separation of 122 and 136 keV peaks. A review is given of the state-of-the-art properties of (CdZn)Te single crystals prepared for substrates in the Institute of Physics of Charles University. The quality of samples is tested by measurements of the diffusion length of minority carriers, from which the mobility-lifetime product is evaluated. (author)

  19. Photoluminescence properties of hybrid SiO2-coated CdTe/CdSe quantum dots.

    Science.gov (United States)

    Liu, Ning; Yang, Ping

    2014-09-01

    Hybrid SiO2-coated CdTe/CdSe quantum dots (QDs) were prepared using CdTe/CdSe QDs prepared by hydrothermal synthesis. A CdSe interlayer made CdTe/CdSe cores with unique type II heterostructures. The hybrid SiO2-coated CdTe/CdSe QDs revealed excellent photoluminescence (PL) properties compared with hybrid SiO2-coated CdTe QDs. Because of the existence of spatial separations of carriers in the type II CdTe/CdSe core/shell QDs, the hybrid QDs had a relatively extended PL lifetime and high stability in phosphate-buffered saline buffer solutions. This is ascribed to the unique components and stable surface state of hybrid SiO2-coated CdTe/CdSe QDs. During the stabilization test in phosphate-buffered saline buffer solutions, both static and dynamic quenching occurred. The quenching mechanism of the hybrid QDs was not suited with the Stern–Volmer equation. However, the relative stable surface of CdTe/CdSe QDs resulted in lower degradation and relative high PL quantum yields compared with hybrid SiO2-coated CdTe QDs. As a result, hybrid SiO2-coated CdTe/CdSe QDs can be used in bioapplications.

  20. Thin-film CdTe cells: Reducing the CdTe

    Energy Technology Data Exchange (ETDEWEB)

    Plotnikov, V.; Liu, X.; Paudel, N.; Kwon, D.; Wieland, K.A.; Compaan, A.D., E-mail: alvin.compaan@utoledo.edu

    2011-08-31

    Polycrystalline thin-film CdTe is currently the dominant thin-film technology in world-wide PV manufacturing. With finite Te resources world-wide, it is appropriate to consider the limits to reducing the thickness of the CdTe layer in these devices. In our laboratory we have emphasized the use of magnetron sputtering for both CdS and CdTe achieving AM1.5 efficiency over 13% on 3 mm soda-lime glass with commercial TCO and 14% on 1 mm aluminosilicate glass. This deposition technique is well suited to good control of very thin layers and yields relatively small grain size which also facilitates high performance with ultra-thin layers. This paper describes our magnetron sputtering studies for fabrication of very thin CdTe cells. Our thinnest cells had CdTe thicknesses of 1 {mu}m, 0.5 {mu}m and 0.3 {mu}m and yielded efficiencies of 12%, 9.7% and 6.8% respectively. With thinner cells Voc, FF and Jsc are reduced. Current-voltage (J-V), temperature dependent J-V (J-V-T) and apparent quantum efficiency (AQE) measurements provide valuable information for understanding and optimizing cell performance. We find that the stability under light soak appears not to depend on CdTe thickness from 2.5 to 0.5 {mu}m. The use of semitransparent back contacts allows the study of bifacial response which is particularly useful in understanding carrier collection in the very thin devices.

  1. Physical properties of Bi doped CdTe thin films grown by CSVT and their influence on the CdS/CdTe solar cells PV-properties

    Energy Technology Data Exchange (ETDEWEB)

    Vigil-Galan, O. [Escuela Superior de Fisica y Matematicas-I.P.N., Edificio de Fisica Avanzada, av. IPN y Juan de Dios Batiz s/n U.P.A.L.M. 07738 Mexico D.F. (Mexico)]. E-mail: osvaldo@esfm.ipn.mx; Sanchez-Meza, E. [Escuela Superior de Fisica y Matematicas-I.P.N., Edificio de Fisica Avanzada, av. IPN y Juan de Dios Batiz s/n U.P.A.L.M. 07738 Mexico D.F. (Mexico); Ruiz, C.M. [Departamento de Fisica de Materiales, Universidad Autonoma de Madrid, Madrid 28049 (Spain); Sastre-Hernandez, J. [Escuela Superior de Fisica y Matematicas-I.P.N., Edificio de Fisica Avanzada, av. IPN y Juan de Dios Batiz s/n U.P.A.L.M. 07738 Mexico D.F. (Mexico); Morales-Acevedo, A. [Escuela Superior de Fisica y Matematicas-I.P.N., Edificio de Fisica Avanzada, av. IPN y Juan de Dios Batiz s/n U.P.A.L.M. 07738 Mexico D.F. (Mexico); CINVESTAV-IPN, Electrical Engineering Department, Av. IPN No2508, C. P. 07360, Mexico, D. F. (Mexico); Cruz-Gandarilla, F. [Escuela Superior de Fisica y Matematicas-I.P.N., Edificio de Fisica Avanzada, av. IPN y Juan de Dios Batiz s/n U.P.A.L.M. 07738 Mexico D.F. (Mexico); Aguilar-Hernandez, J. [Escuela Superior de Fisica y Matematicas-I.P.N., Edificio de Fisica Avanzada, av. IPN y Juan de Dios Batiz s/n U.P.A.L.M. 07738 Mexico D.F. (Mexico); Saucedo, E. [Departamento de Fisica de Materiales, Universidad Autonoma de Madrid, Madrid 28049 (Spain); Contreras-Puente, G. [Escuela Superior de Fisica y Matematicas-I.P.N., Edificio de Fisica Avanzada, av. IPN y Juan de Dios Batiz s/n U.P.A.L.M. 07738 Mexico D.F. (Mexico); Bermudez, V. [Departamento de Fisica de Materiales, Universidad Autonoma de Madrid, Madrid 28049 (Spain)

    2007-05-31

    The physical properties of Bi doped CdTe films, grown on glass substrates by the Closed Space Transport Vapour (CSVT) method, from different Bi doped CdTe powders are presented. The CdTe:Bi films were characterized using Photoluminescence, Hall effect, X-Ray diffraction, SEM and Photoconductivity measurements. Moreover, CdS/CdTe:Bi solar cells were made and their characteristics like short circuit current density (J {sub sc}), open circuit voltage (V {sub OC}), fill factor (FF) and efficiency ({eta}) were determined. These devices were fabricated from Bi doped CdTe layers deposited on CdS with the same growth conditions than those used for the single CdTe:Bi layers. A correlation between the CdS/CdTe:Bi solar cell characteristics and the physical properties of the Bi doped CdTe thin films are presented and discussed.

  2. Influence of deposition parameters on the properties of CdTe films deposited by close spaced sublimation

    OpenAIRE

    Falcão Vivienne Denise; Pinheiro Wagner Anacleto; Ferreira Carlos Luiz; Cruz Leila Rosa de Oliveira

    2006-01-01

    CdTe thin films are used as absorber layer in CdS/CdTe solar cells. The microstructure of this absorber layer plays a fundamental role in photovoltaic conversion and can be controlled by the deposition parameters used during the film growth. In this work, CdTe thin films were deposited by the CSS method onto glass substrates previously covered with In2O3:Sn. The effects of pressure, source temperature and substrate temperature on the microstructural properties of the films were studied. The p...

  3. Photoluminescence of Cu-doped CdTe and related stability issues in CdS/CdTe solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Grecu, D. [University of Toledo, Toledo, Ohio 43606-3390 (United States); Compaan, A. D. [University of Toledo, Toledo, Ohio 43606-3390 (United States); Young, D. [National Renewable Energy Laboratory, Golden, Colorado 80401 (United States); Jayamaha, U. [First Solar LLC., Perrysburg, Ohio 43551 (United States); Rose, D. H. [First Solar LLC., Perrysburg, Ohio 43551 (United States)

    2000-09-01

    We explore Cu electronic states in CdTe using photoluminescence as the main investigative method. Our results are consistent with some Cu atoms occupying substitutional positions on the Cd sublattice and with others forming Frenkel pairs of the type Cu{sub i}{sup +}-V{sub Cd}{sup -} involving an interstitial Cu and a Cd vacancy. In addition, we find that Cu-doped CdTe samples exhibit a significant ''aging'' behavior, attributable to the instability of Cu acceptor states as verified by our Hall measurements. The aging appears to be reversible by a 150-200 degree sign C anneal. Our results are used to explain efficiency degradation of some CdTe solar-cell devices which use Cu for the formation of a backcontact. (c) 2000 American Institute of Physics.

  4. Thin-film CdTe photovoltaic cells by laser deposition and rf sputtering

    Energy Technology Data Exchange (ETDEWEB)

    Compaan, A.; Bohn, R.G.; Bhat, A.; Tabory, C.; Shao, M.; Li, Y.; Savage, M.E.; Tsien, L. (Department of Physics and Astronomy, The University of Toledo, Toledo, Ohio 43606 (United States))

    1992-12-01

    Laser-driven physical vapor deposition (LDPVD) and radio-frequency (rf) sputtering have been used to fabricate thin-film solar cells on SnO[sub 2]-coated glass substrates. The laser-ablation process readily permits the use of several target materials in the same vacuum chamber and complete solar cell structures have been fabricated on SnO[sub 2]-coated glass using LDPVD for the CdS, CdTe, and CdCl[sub 2]. To date the best devices ([similar to]9% AM1.5) have been obtained after a post-deposition anneal at 400 [degree]C. In addition, cells have been fabricated with the combination of LDPVD CdS, rf-sputtered CdTe, and LDPVD CdCl[sub 2]. The performance of these cells indicates considerable promise for the potential of rf sputtering for CdTe photovoltaic devices. The physical mechanisms of LDPVD have been studied by transient optical spectroscopy on the laser ablation plume. These measurements have shown that, e.g., Cd is predominantly in the neutral atomic state in the plume but with a large fraction which is highly excited internally ([ge]6 eV) and that the typical neutral Cd translational kinetic energies perpendicular to the target are 20 eV and greater. Quality of as-grown and annealed films has been analyzed by optical absorption. Raman scattering, photoluminescence, electrical conductivity, Hall effect, x-ray diffraction, and SEM/EDS.

  5. Radioisotope Thermoelectric Generators Based on Segmented BiTe/PbTe-BiTe/TAGS/PbSnTe

    Science.gov (United States)

    McAlonan, Malachy; Patel, Kalpesh; Cummer, Keith

    2006-01-01

    This paper reports on Phase 1 of a multifaceted effort to develop a more efficient radioisotope thermoelectric generator (RTG) for future NASA missions. The conversion efficiency goal is 10% or higher at a power level of 20 watt or higher. The thermoelectric (T/E) efficiency achievable with present T/E materials is about 8% for favorable temperatures. Thermoelectric converter designs, T/E material properties, and T/E couple thermal and electrical performance were investigated in Phase 1 of this program to find paths to improve conversion efficiency. T/E properties can be improved by optimizing the composition of the materials and by improving the micro structural characteristics such as homogeneity, grain size, and phases present. T/E couple performance can be improved by reducing the electrical and thermal contact resistances of the couple and within the segmented T/E elements. Performance and reliability improvements can be achieved by reducing the thermo-mechanical stresses, improving the quality of the bonds and interfaces, minimizing the number of required bonds, and reducing the degradation rates of both the T/E materials and the bonds. This paper focuses on one portion of the activity, i.e., the design of a small converter. In the converter design effort, a prototypic 20-watt device, suitable for use with a single general-purpose heat source (GPHS), was built using an optimized converter design of segmented thermoelectric elements of heritage composition. The 20-watt prototype achieved the power predicted for the test conditions. The chosen couple design used segmented BiTe/PbTe for the n-type element and BiTe/TAGS/PbSnTe, for the p-type T/E element. Use of the BiTe segment exploits the opportunity of the small RTG to operate at lower heat rejection temperatures and results in much higher conversion efficiency, the main objective of the NASA program. Long term data on similarly segmented couples at Teledyne together with the 20-watt module test results

  6. CdTe,核-壳型CdTe/CdS及CdTe/ZnS量子点的合成及表征%CdTe, Core-shell CdTe/CdS and CdTe/ZnS Quantum Dots: Their Synthesis and Characterization*

    Institute of Scientific and Technical Information of China (English)

    张纪梅; 许世超; 宋秀云; 代昭; 孙波; 姚翠翠

    2009-01-01

    Semiconductor CdTe, core-shell CdTe/CdS and CdTe/ZnS nanocrystals(quantum dots; QDs) were prepared in aqueous phase. Investigations of the prepared nanocrystals were performed via scanning tunneling microscope(STM) and fluorescence spectrum(FS), and quantum yields(Qys) was calculated based on the resulting data from FS. Particle size of well dispersed CdTe was evaluated to be ca 3 nm via STM. Some reaction conditions were investigated and discussed to enhance Qys of CdTe/CdS core-shell QDs, such as dependence of Cd2+ concentration, and effect of Cd2+∶S2- etc. Among all of those methods, Qys of core-shell CdTe/CdS is generally degressive with refluxing time elapsing. The best Qys of ca 80.0% can be achieved when pH was set at 8.5, Cd2+∶S2-=10:1(mol ratio). Moreover, CdTe/ZnS core-shell QDs was prepared, and results indicated a red-shift from 551 nm to 635 nm comparing with CdTe core, which suggested the growth of QDs size, however, Qys of CdTe/ZnS decreased to 14.4%. QDs currently discussed in this research are easily synthesized, and they will be useful in applications of biolabeling, imaging, and biosensing based on fluorescence resonance energy transfer(FRET).%在水相中制备了半导体CdTe纳米晶,核-壳型CdTe/CdS和CdTe/ZnS纳米晶(即量子点;QDs).利用扫描隧道显微镜(STM)和荧光光谱(FS)对合成的纳米晶量子点进行了研究,并且根据FS的数据进行了量子效率的计算.STM的结果表明合成的量子点直径约为3 nm并且分布良好.为了提高量子效率,对Cd2+浓度和Cd2+∶S2-比例等反应条件进行了研究,结果表明随着回流时间的增加,核-壳型量子点CdTe/CdS的量子效率总体上呈下降趋势.CdTe/CdS在pH8.5,Cd2+∶S2-=10∶1(摩尔比)时可获得80.0%的最大量子效率.同时制备了核-壳型量子点CdTe/ZnS,其最大发射波长由551 nm(CdTe)红移到635 nm(CdTe/ZnS)表明量子点的尺寸在增长,但是量子效率下降到14.4%. 当前研究的量子点可适用于生

  7. The properties of CdTe solar cells with ZnTe/ZnTe: Cu buffer layers

    Institute of Scientific and Technical Information of China (English)

    Song Huijin; Zheng Jiagui; Feng Lianghuan; Yan Qiang; Lei Zhi; Wu Lili; Zhang Jingquan; Li Wei; Li Bing

    2008-01-01

    CdS/CdTe solar cells with ZnTe/ZnTe:Cu buffer layers were fabricated and studied. The energy band structure of it was analyzed. The C-V, I-V characteristics and the spectral response show that the ZnTe/ZnTe:Cu buffer layers improve the back contact characteristic properties, the diode characteristics of the forward junction and the short-wave spectral response of the CdTe solar cells. The ZnTe/ZnTe:Cu buffer layers affect the solar cell conversion efficiency and its fill factor.

  8. Studies of Spectroscopic Ellipsometry in Cd1-xMnx Te/CdTe Superlattices

    Institute of Scientific and Technical Information of China (English)

    CHEN Chen-Jia; WANG Xue-Zhong; Vittorio BELLANI; Angiolino STELLA

    2006-01-01

    Cd1-xMnxTe/CdTe superlattices and thin films were grown by molecular beam epitaxy on GaAs (001) substrates. Spectroscopic ellipsometry measurements were performed on Cd1-xMnxTe/CdTe superlattices with compositions x = 0.4, 0.8, and Cd1-xMnxTe thin films with x = 0.2, 0.4, 0.6 at room temperature in the photon energy range 1.4-5eV. In superlattices the pseudodielectric functions measured by ellipsometry show specific features related to the exciton transition between quantized interbands. The exciton transitions related to the heavy holes of 11H, 22H, and 33H are observed and identified. In thin films spectroscopic ellipsometry allows the clear identification of the energy gap E0. Additionally, critical point transitions are observable in both the spectra of the superlattices and films. Photoreflectance spectra were also performed at room temperature in order to compare with our ellipsometry results. After taking into account the strain-induced and quantum confinement effects, the theoretical calculations are in good agreement with our experimental spectra. Ellipsometry appears to be a suited technique to monitor the MBE growth, ultimately also in situ, of diluted magnetic low-dimensional systems.

  9. Synthesis and Surface Modification of CdTe Nanocrystals

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    CdTe nanocrystals were prepared in aqueous solution via the reaction between Cd2+ and NaHTe in the presence of mercaptoacetic acid. Interactions between CdTe nanocrystals and phenylalanine were formed via electrostatic/coordinate self-assembly. The photoluminescence intensity of CdTe nanocrystals was improved obviously. The interaction mechanism was discussed and was considered to be surface passivation.

  10. Correction of diagnostic x-ray spectra measured with CdTe and CdZnTe detectors

    Energy Technology Data Exchange (ETDEWEB)

    Matsumoto, M. [Osaka Univ., Suita (Japan). Medical School; Kanamori, H.; Toragaito, T.; Taniguchi, A.

    1996-07-01

    We modified the formula of stripping procedure presented by E. Di. Castor et al. We added the Compton scattering and separated K{sub {alpha}} radiation of Cd and Te (23 and 27keV, respectively). Using the new stripping procedure diagnostic x-ray spectra (object 4mm-Al) of tube voltage 50kV to 100kV for CdTe and CdZnTe detectors are corrected with comparison of those spectra for the Ge detector. The corrected spectra for CdTe and CdZnTe detectors coincide with those for Ge detector at lower tube voltage than 70kV. But the corrected spectra at higher tube voltage than 70kV do not coincide with those for Ge detector. The reason is incomplete correction for full energy peak efficiencies of real CdTe and CdZnTe detectors. (J.P.N.)

  11. Highly luminescent CdTe/CdSe colloidal heteronanocrystals with temperature-dependent emission color

    NARCIS (Netherlands)

    Chin, P.T.K.; de Mello Donega, C.; van Bavel, S.S.; Meskers, S.C.J.; Sommerdijk, N.A.J.M.; Jansen, R.A.J.

    2007-01-01

    In this work we present the preparation of highly luminescent anisotropic CdTe/CdSe colloidal heteronanocrystals. The reaction conditions used (low temperature, slow precursor addition, and surfactant composition) resulted in a tunable shape from prolate to branched CdTe/CdSe nanocrystals. Upon CdSe

  12. Simulation of the Efficiency of CdS/CdTe Tandem Multi-Junction Solar Cells

    OpenAIRE

    Mirkamali, Ashrafalsadat S.; Muminov, Khikmat Kh.

    2016-01-01

    In this paper we study CdS/CdTe solar cells by means of AMPS-1D software. First we study the effect of thickness of semiconductor layers on the output parameters of the CdS/CdTe solar cell, such as density of short-circuit current, open circuit voltage, fill factor and efficiency. Numerical simulation shows that the highest efficiency of single-junction CdS/CdTe solar cell equal to 18.3% is achieved when the CdTe layer thickness is 1000 nm and a CdS layer is 60 nm. Then, in order to obtain th...

  13. Electrodeposition, characterization and photo electrochemical properties of CdSe and CdTe

    Directory of Open Access Journals (Sweden)

    Atef Y. Shenouda

    2015-03-01

    Full Text Available CdSe and CdTe are electrodeposited using 0.1 M Cd2+ and different ion concentrations of Se and Te. The effect of the temperature on the electrodeposition process is also studied. The crystal structure of the deposited CdSe and CdTe is investigated by X-ray diffraction (XRD. Scanning electron microscopy (SEM of samples deposited at optimized parameters reveals that CdSe has spongy spherical grains while CdTe has coralloid morphology. Optical absorption shows the presence of direct transition with band gap energy 1.96 and 1.51 eV for CdSe and CdTe, respectively. The highest photo-conversion efficiencies of electrodeposited CdSe and CdTe films per unit area are 6% and 9.6%, respectively that achieved under simple laboratory conditions.

  14. A model for the CdTe/CdS junction

    Energy Technology Data Exchange (ETDEWEB)

    Linam, David L; Singh, Vijay P; McClure, Jonh C; Lush, Gregory; Mathew, X [Centro de Investigacion en Energia, UNAM, Temixco, Morelos (Mexico)

    2000-07-01

    The saturation current and junction quality factor of a series of commercial CdTe/CdS solar cells have been measured. A high saturation current (compared to, for example, Si cells) is the primary cause of lower than theoretical efficiency. Furthermore, this current and the junction quality factor are functions of both light intensity and voltage bias level. It was found that tunneling is the predominant junction transport mechanism at high light levels and at low voltages while diffusion and regeneration/combination dominate at high voltage and low light levels. A model is presented to account for these observations. [Spanish] Se midieron las corrientes de saturacion y el factor de calidad de la union de una serie de celdas solares CdTe/CdS. Una corriente de saturacion alta (comparada por ejemplo a celdas de Si) es la causa primordial de eficiencia inferior a la teorica. Mas aun esta corriente y el factor de la calidad de la junta son funciones tanto de la intensidad de la luz y del nivel del voltaje de polarizacion. Se encontro que el paso a traves de una barrera de potencial (Tunneling) es el mecanismo de transporte predominate en la junta a altos niveles de luz y bajos voltajes mientras que la difusion y la regeneracion-combinacion predominaba a alto voltaje y bajos niveles de luz. Se presenta un modelo para tomar en cuenta estas observaciones.

  15. Effect of low concentration Sn doping on optical properties of CdS films grown by CBD technique.

    Science.gov (United States)

    Jafari, Atefeh; Zakaria, Azmi; Rizwan, Zahid; Mohd Ghazali, Mohd Sabri

    2011-01-01

    Thin and transparent films of doped cadmium sulfide (CdS) were obtained on commercial glass substrates by Chemical Bath Deposition (CBD) technique. The films were doped with low concentration of Sn, and annealed in air at 300 °C for 45 min. The morphological characterization of the films with different amounts of dopant was made using SEM and EDAX analysis. Optical properties of the films were evaluated by measuring transmittance using the UV-vis spectrophotometer. A comparison of the results revealed that lower concentration of Sn doping improves transmittance of CdS films and makes them suitable for application as window layer of CdTe/CIGS solar cells.

  16. Preparation and Properties of CdTe Polycrystalline Films for Solar Cells

    Institute of Scientific and Technical Information of China (English)

    ZHENG Huajing; ZHANG Jingquan; FENG Lianghuan; ZHENG Jiagui; CAI Wei; LI Bing; CAI Yaping

    2006-01-01

    The structure and characteristics of CdTe thin films are closely dependent on the whole deposition process in close-space sublimation (CSS). The physical mechanism of CSS was analyzed and the temperature distribution in CSS system was measured, and the influences of the increasing-temperature process and pressure on the preliminary nucleus creation were studied. The results indicate: the samples deposited at different pressures have a cubical structure of CdTe and the diffraction peaks of CdS and SnO2∶F. As the atmosphere pressure increases, the crystal size of CdTe decreases, the rate of the transparency of the thin film decreases and the absorption side moves towards the short-wave direction. After a 4-minute depositing process with a substrate temperature of 500 ℃ and a source temperature of 620 ℃, the polycrystalline thin films can be made, so the production of high-quality integrated cell with SnO2:F/CdS/CdTe/Au structure is hopeful.

  17. The effect on CdS/CdTe solar cell conversion efficiency of the presence of fluorine in the usual CdCl2 treatment of CdTe

    OpenAIRE

    O. K. Echendu; Dharmadasa, I

    2015-01-01

    The addition of CdF2 to the CdCl2 solution used in the well-known CdCl2 treatment of CdS/CdTe solar cells has been observed to drastically improve the conversion efficiency of fully fabricated CdS/CdTe solar cells. The observed improvement is as a result of further enhancement of structural and optoelectronic properties of the CdCl2+CdF2-treated CdTe layers compared to the CdCl2-treated CdTe layers. A set of CdS/CdTe samples were grown by electrochemical deposition under different conditions ...

  18. Antiferromagnetic spin ordering and interlayer magnetic correlations in MnTe/CdTe superlattices

    Science.gov (United States)

    Giebultowicz, T. M.; Faschinger, W.; Nunez, V.; Klosowski, P.; Bauer, G.; Sitter, H.; Furdyna, J. K.

    1994-04-01

    Results of neutron scattering studies on MnTe/CdTe superlattices with ultrathin non-magnetic CdTe "barriers" are presented and compared with data from earlier studies on MnSe/ZnSe, MnTe/ZnTe, and MnSe/ZnTe multilayers with thick non-magnetic spacers. The experiments revealed two qualitatively new effects—namely, (i) the existence of pronounced interlayer magnetic correlations in the case of the CdTe thickness corresponding to two single monolayers and (ii) the coexistence of two magnetic phases that never occurred simultaneously in the previously studied systems.

  19. Calorimetric study of tellurium rich Se-Te-Sn glasses

    Science.gov (United States)

    Heera, Pawan; Kumar, Anup; Jharwal, Manish; Sharma, Raman

    2016-05-01

    We report the calorimetric study of amorphous Se30Te70-x Snx alloys for x= 0, 1.5, 2.5, 4.5 in terms of kinetic parameters. The DSC curves recorded at four different heating rates are analyzed to determine the transition temperatures, activation energy, thermal stability, glass forming ability. The crystallization process has been investigated using Kissinger, Matusita, Augis and Bennett, and Gao and Wang models. Various kinetic parameters have been calculated for a better understanding of the growth mechanism. The glass transition temperatures Tg, onset crystallization Tc, peak crystallization Tp, and melting temperature Tm are found to increase with the increase in Sn content. The system under investigation is found to be thermally stable for at lower at% of Sn. The values of parameters HR, Hw, and S indicate that Glass forming ability (GFA) decays with an increase in Sn content.

  20. Photovoltaic properties of sintered CdS/CdTe solar cells doped with Cu

    Science.gov (United States)

    Park, J. W.; Ahn, B. T.; Im, H. B.; Kim, C. S.

    1992-11-01

    The effect of Cu doping before sintering on the photovoltaic properties of sintered CdS/CdTe solar cells were investigated by putting various amounts of CuCl2 either into the CdTe layer or into the back contact carbon layer. It was found that, as the amount of CuCl2 in the CdTe layers increased up to 25 ppm, the cell parameters of the sintered CdS/CdTe solar cells remained at about the same values, and then decreased sharply with further increase of CuCl2. The decreases in cell parameters are caused mainly by the increase in the resistivity of CdS and CdTe layer and the decrease in the optical transmission of CdS due to Cu doping from the CdTe.

  1. Calculation of the High-Temperature Point Defects Structure in Te-Rich CdTe

    Science.gov (United States)

    Dai, Shujun; Wang, Tao; Liu, Huimin; He, Yihui; Jie, Wanqi

    2016-10-01

    A thermodynamic equilibrium model for CdTe annealed under Te vapor is established, in which possible point defects and a defect reaction existing in undoped and In-doped Te-rich CdTe crystals are taken into consideration. Independent point defects, such as VCd, Cdi, and Tei, as well as defect complexes, namely TeCd-VCd (B complex), {Te}_{{Cd}}^{2 + } - {V}_{{Cd}}^{2 - } (D complex), {In}_{{Cd}}^{ + } - {V}_{{Cd}}^{ - } (A-center) and Tei-VCd (TeCd), are discussed based on the defect chemistry theory. More specially, the mass action law and quasi-chemical equations are used to calculate defects concentration and Fermi level in undoped and doped CdTe crystals with different indium concentrations. It is found that the Fermi level is controlled by a {V}_{{Cd}}^{2 - } , TeCd, and B/D-complex in undoped crystal. The concentration of VCd drops down in an obvious manner and that of TeCd rises for doped crystal with increasing [In].

  2. Recrystallization and sulfur diffusion in CdCl{sub 2}-treated CdTe/CdS thin films

    Energy Technology Data Exchange (ETDEWEB)

    McCandless, B.E.; Moulton, L.V.; Birkmire, R.W. [University of Delaware, Newark, DE (United States). Inst. of Energy Conversion

    1997-08-01

    The role of CdCl{sub 2} in prompting recrystallization, grain growth and interdiffusion between CdS and CdTe layers in physical vapor-deposited CdS/CdTe thin-film solar cells is presented. Several CdTe/CdS thin-film samples with different CdTe film thicknesses were treated in air at 415{sup o}C for different times with and without a surface coating of CdCl{sub 2}. The samples were characterized by scanning electron microscopy, transmission electron microscopy, energy dispersive x-ray spectroscopy, x-ray diffractometry and optical absorption. The results show that CdCl{sub 2} treatment enhances the recrystallization and diffusion processes, leading to a compositional variation within the CdTe layer due to diffusion of sulfur from the CdS. The highest sulfur concentrations observed after 30 min treatments with CdCl{sub 2} at 415{sup o}C are near the solubility limit for sulfur in CdTe. The compositional distributions indicated by x-ray diffraction measurements of samples with different CdTe thickness show that the S-rich CdTe{sub 1-x}S{sub x} region lies near the CdTe/CdS interface. A multiple-step mixing process must be inferred to account for the diffraction profiles obtained. (author)

  3. Electrodeposition, characterization and photo electrochemical properties of CdSe and CdTe

    OpenAIRE

    Atef Y. Shenouda; El Sayed, El Sayed M.

    2015-01-01

    CdSe and CdTe are electrodeposited using 0.1 M Cd2+ and different ion concentrations of Se and Te. The effect of the temperature on the electrodeposition process is also studied. The crystal structure of the deposited CdSe and CdTe is investigated by X-ray diffraction (XRD). Scanning electron microscopy (SEM) of samples deposited at optimized parameters reveals that CdSe has spongy spherical grains while CdTe has coralloid morphology. Optical absorption shows the presence of direct transition...

  4. Physical properties of electron beam evaporated CdTe and CdTe:Cu thin films

    Energy Technology Data Exchange (ETDEWEB)

    Punitha, K. [Department of Physics, Alagappa University, Karaikudi 630004 (India); Sivakumar, R., E-mail: krsivakumar1979@yahoo.com [Directorate of Distance Education, Alagappa University, Karaikudi 630004 (India); Sanjeeviraja, C. [Department of Physics, Alagappa Chettiar College of Engineering and Technology, Karaikudi 630004 (India); Sathe, Vasant; Ganesan, V. [UGC-DAE Consortium for Scientific Research, Indore 452001 (India)

    2014-12-07

    In this paper, we report on physical properties of pure and Cu doped cadmium telluride (CdTe) films deposited onto corning 7059 microscopic glass substrates by electron beam evaporation technique. X-ray diffraction study showed that all the deposited films belong to amorphous nature. The average transmittance of the films is varied between 77% and 90%. The optical energy band gap of pure CdTe film is 1.57 eV and it decreased to 1.47 eV upon 4 wt. % of Cu addition, which may be due to the extension of localized states in the band structure. The refractive index of the films was calculated using Swanepoel method. It was observed that the dispersion data obeyed the single oscillator of the Wemple-Didomenico model, from which the dispersion energy (E{sub d}) parameters, dielectric constants, plasma frequency, and oscillator energy (E{sub o}) of CdTe and CdTe:Cu films were calculated and discussed in detail with the light of possible mechanisms underlying the phenomena. The variation in intensity of photoluminescence band edge emission peak observed at 820 nm with Cu dopant is due to the change in surface state density. The observed trigonal lattice of Te peaks in the micro-Raman spectra confirms the p-type conductive nature of films, which was further corroborated by the Hall effect measurement. The lowest resistivity of 6.61 × 10{sup 4} Ω cm was obtained for the CdTe:Cu (3 wt. %) film.

  5. Pixelated CdZnTe drift detectors

    DEFF Research Database (Denmark)

    Kuvvetli, Irfan; Budtz-Jørgensen, Carl

    2005-01-01

    A technique, the so-called Drift Strip Method (DSM), for improving the CdZnTe detector energy response to hard X-rays and gamma-rays was applied as a pixel geometry. First tests have confirmed that this detector type provides excellent energy resolution and imaging performance. We specifically...... report on the performance of 3 mm thick prototype CZT drift pixel detectors fabricated using material from eV-products. We discuss issues associated with detector module performance. Characterization results obtained from several prototype drift pixel detectors are presented. Results of position...

  6. CdTe ambulatory ventricular function monitor

    Energy Technology Data Exchange (ETDEWEB)

    Lazewatsky, J.L.; Alpert, N.M.; Moore, R.H.; Boucher, C.A.; Strauss, H.W.

    1979-01-01

    A prototype device consisting of two arrays of CdTe detectors, ECG amplifiers and gate, microprocessor, and tape recorder was devised to record simultaneous ECG and radionuclide blood pool data from the left ventricle for extended periods during normal activity. The device is intended to record information concerning both normal and abnormal physiology of the heart and to permit the evaluation of new pharmaceuticals under everyday conditions. Preliminary results indicate that the device is capable of recording and reading out data from both phantoms and patients.

  7. Controlled Synthesis of Nanoscale CdTe Urchins

    Institute of Scientific and Technical Information of China (English)

    BAO Jian; SHEN Yue; SUN Yan; YUE Yang; CHEN Xin; DAI Ning

    2009-01-01

    We presented a simple route to prepare nanoscale CdTe urchins in a tri-n-octylphosphine oxide(TOPO)system.CdTe urchins consisted of a core and several attached arms.The arms were ca.3 nm wide,and their lengths could be controlled with the reaction time.The authors investigated the optical absorption and structural properties of the prepared CdTe.The lengths of the arms could be tuned into CdTe nanourchins,which led to a change in the photophysical properties of the nanoscale CdTe urchins.The results,including transmission electron microscopy(TEM) and absorption spectra,indicated that mesoporous silica and aminopropyltriethoxysilane(APTES) contributed to the formation of nanoscale CdTe urchins.

  8. Ultrafast charge carrier relaxation and charge transfer processes in CdS/CdTe thin films.

    Science.gov (United States)

    Pandit, Bill; Dharmadasa, Ruvini; Dharmadasa, I M; Druffel, Thad; Liu, Jinjun

    2015-07-14

    Ultrafast transient absorption pump-probe spectroscopy (TAPPS) has been employed to investigate charge carrier relaxation in cadmium sulfide/cadmium telluride (CdS/CdTe) nanoparticle (NP)-based thin films and electron transfer (ET) processes between CdTe and CdS. Effects of post-growth annealing treatments to ET processes have been investigated by carrying out TAPPS experiments on three CdS/CdTe samples: as deposited, heat treated, and CdCl2 treated. Clear evidence of ET process in the treated thin films has been observed by comparing transient absorption (TA) spectra of CdS/CdTe thin films to those of CdS and CdTe. Quantitative comparison between ultrafast kinetics at different probe wavelengths unravels the ET processes and enables determination of its rate constants. Implication of the photoinduced dynamics to photovoltaic devices is discussed.

  9. An optimized multilayer structure of CdS layer for CdTe solar cells application

    Energy Technology Data Exchange (ETDEWEB)

    Han Junfeng, E-mail: pkuhjf@gmail.com [State Key Laboratory of Nuclear Physics and Technology, School of Physics, Peking University, Road Yiheyuan 5, Beijing 100871 (China); Institute of Materials Science, Darmstadt University of Technology, Petersenstr. 23, 64287 Darmstadt (Germany); Liao Cheng, E-mail: Cliao@pku.edu.cn [State Key Laboratory of Nuclear Physics and Technology, School of Physics, Peking University, Road Yiheyuan 5, Beijing 100871 (China); Jiang Tao [State Key Laboratory of Nuclear Physics and Technology, School of Physics, Peking University, Road Yiheyuan 5, Beijing 100871 (China); Spanheimer, C.; Haindl, G.; Fu, Ganhua; Krishnakumar, V. [Institute of Materials Science, Darmstadt University of Technology, Petersenstr. 23, 64287 Darmstadt (Germany); Zhao Kui [State Key Laboratory of Nuclear Physics and Technology, School of Physics, Peking University, Road Yiheyuan 5, Beijing 100871 (China); Klein, A.; Jaegermann, W. [Institute of Materials Science, Darmstadt University of Technology, Petersenstr. 23, 64287 Darmstadt (Germany)

    2011-04-28

    Research highlights: > Two different methods to prepare CdS films for CdTe solar cells. > A new multilayer structure of window layer for the CdTe solar cell. > Thinner CdS window layer for the solar cell than the standard CdS layer. > Higher performance of solar cells based on the new multilayer structure. - Abstract: CdS layers grown by 'dry' (close space sublimation) and 'wet' (chemical bath deposition) methods are deposited and analyzed. CdS prepared with close space sublimation (CSS) has better crystal quality, electrical and optical properties than that prepared with chemical bath deposition (CBD). The performance of CdTe solar cell based on the CSS CdS layer has higher efficiency than that based on CBD CdS layer. However, the CSS CdS suffers from the pinholes. And consequently it is necessary to prepare a 150 nm thin film for CdTe/CdS solar cell. To improve the performance of CdS/CdTe solar cells, a thin multilayer structure of CdS layer ({approx}80 nm) is applied, which is composed of a bottom layer (CSS CdS) and a top layer (CBD CdS). That bi-layer film can allow more photons to pass through it and significantly improve the short circuit current of the CdS/CdTe solar cells.

  10. Homogeneous CdTe quantum dots-carbon nanotubes heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Vieira, Kayo Oliveira [Grupo de Pesquisa em Química de Materiais – (GPQM), Departamento de Ciências Naturais, Universidade Federal de São João del-Rei, Campus Dom Bosco, Praça Dom Helvécio, 74, CEP 36301-160, São João del-Rei, MG (Brazil); Bettini, Jefferson [Laboratório Nacional de Nanotecnologia, Centro Nacional de Pesquisa em Energia e Materiais, CEP 13083-970, Campinas, SP (Brazil); Ferrari, Jefferson Luis [Grupo de Pesquisa em Química de Materiais – (GPQM), Departamento de Ciências Naturais, Universidade Federal de São João del-Rei, Campus Dom Bosco, Praça Dom Helvécio, 74, CEP 36301-160, São João del-Rei, MG (Brazil); Schiavon, Marco Antonio, E-mail: schiavon@ufsj.edu.br [Grupo de Pesquisa em Química de Materiais – (GPQM), Departamento de Ciências Naturais, Universidade Federal de São João del-Rei, Campus Dom Bosco, Praça Dom Helvécio, 74, CEP 36301-160, São João del-Rei, MG (Brazil)

    2015-01-15

    The development of homogeneous CdTe quantum dots-carbon nanotubes heterostructures based on electrostatic interactions has been investigated. We report a simple and reproducible non-covalent functionalization route that can be accomplished at room temperature, to prepare colloidal composites consisting of CdTe nanocrystals deposited onto multi-walled carbon nanotubes (MWCNTs) functionalized with a thin layer of polyelectrolytes by layer-by-layer technique. Specifically, physical adsorption of polyelectrolytes such as poly (4-styrene sulfonate) and poly (diallyldimethylammonium chloride) was used to deagglomerate and disperse MWCNTs, onto which we deposited CdTe quantum dots coated with mercaptopropionic acid (MPA), as surface ligand, via electrostatic interactions. Confirmation of the CdTe quantum dots/carbon nanotubes heterostructures was done by transmission and scanning electron microscopies (TEM and SEM), dynamic-light scattering (DLS) together with absorption, emission, Raman and infrared spectroscopies (UV–vis, PL, Raman and FT-IR). Almost complete quenching of the PL band of the CdTe quantum dots was observed after adsorption on the MWCNTs, presumably through efficient energy transfer process from photoexcited CdTe to MWCNTs. - Highlights: • Highly homogeneous CdTe-carbon nanotubes heterostructures were prepared. • Simple and reproducible non-covalent functionalization route. • CdTe nanocrystals homogeneously deposited onto multi-walled carbon nanotubes. • Efficient energy transfer process from photoexcited CdTe to MWCNTs.

  11. Aqueous Phase Synthesis of Red CdX (X=Te,Te/CdS,Te/ZnS) Quantum Dots and Their Toxic Effects%水相合成CdX(X=Te,Te/CdS,Te/ZnS)红色量子点及毒性效应

    Institute of Scientific and Technical Information of China (English)

    王显祥; 黄娟; 靳茹文; 杨中科; 单志; 杨婉身

    2009-01-01

    分别以巯基乙酸(Mercaptoacetic Acid,MA)、还原犁谷胱甘肽(Glutathione,GSH)为稳定剂在水相中直接合成了巯基乙酸CdTe(CdTe-MA)、红色巯基乙酸CdTe/CdS(CdTe/CdS-MA)、巯基乙酸CdTe/ZnS(CdTe/ZnS-MA)及谷胱甘肽CdTe(CdTe-GSH)量子点.其中,CdTe-GSH量子点的量子产率可达47.3%.体外溶血实验证实CdTe/ZnS-MA和CdTe-GSH量子点的溶血率较CdTe-MA和CdTe/CdS-MA低,浓度为0.05 mmol/L的量子点溶血率<5%,达到了生物医用材料的要求.活体实验证实:通过尾静脉方式把量子点注入小鼠体内后,荧光显微镜观察发现高剂量的量子点(0.4mmol/10 g)在体内主要在心、肝、脾、肾组织中分布较多,且引起不同程度的组织病变.

  12. Electrical characterization of CdTe grain-boundary properties from as processed CdTe/CdS solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Woods, L.M.; Robinson, G.Y. [Colorado State Univ., Fort Collins, CO (United States); Levi, D.H.; Ahrenkiel, R.K. [National Renewable Energy Lab., Golden, CO (United States); Kaydanov, V. [Colorado School of Mines, Golden, CO (United States)

    1998-09-01

    An ability to liftoff or separate the thin-film polycrystalline CdTe from the CdS, without the use of chemical etches, has enabled direct electrical characterization of the as-processed CdTe near the CdTe/CdS heterointerface. The authors use this ability to understand how a back-contact, nitric-phosphoric (NP) etch affects the grain boundaries throughout the film. Quantitative determination of the grain-boundary barrier potentials and estimates of doping density near the grain perimeter are determined from theoretical fits to measurements of the current vs. temperature. Estimates of the bulk doping are determined from high-frequency resistivity measurements. The light and dark barrier potentials change after the NP etch, and the origin of this change is postulated. Also, a variable doping density within the grains of non-etched material has been determined. These results allow a semi-quantitative grain-boundary band diagram to be drawn that should aid in determining more accurate two-dimensional models for polycrystalline CdTe solar cells.

  13. Advances in the In-House CdTe Research Activities at NREL

    Energy Technology Data Exchange (ETDEWEB)

    Gessert, T.; Wu, X.; Dhere, R.; Moutinho, H.; Smith, S.; Romero, M.; Zhou, J.; Duda, A.; Corwine, C.

    2005-01-01

    NREL in-house CdTe research activities have impacted a broad range of recent program priorities. Studies aimed at industrially relevant applications have produced new materials and processes that enhance the performance of devices based on commercial materials (e.g., soda-lime glass, SnO2:F). Preliminary tests of the effectiveness of these novel components using large-scale processes have been encouraging. Similarly, electro- and nano-probe techniques have been developed and used to study the evolution and function of CdTe grain boundaries. Finally, cathodoluminescence (CL) and photoluminescence (PL) studies on single-crystal samples have yielded improved understanding of how various processes may combine to produce important defects in CdTe films.

  14. Effect of ZnTe and CdZnTe Alloys at the Back Contact of 1-μm-Thick CdTe Thin Film Solar Cells

    Science.gov (United States)

    Amin, Nowshad; Yamada, Akira; Konagai, Makoto

    2002-05-01

    N2-doped ZnTe was introduced onto 1-μm-thick CdTe absorbers in order to reduce the carrier recombination at the back contact of CdS/CdTe/C/Ag configuration solar cells. ZnTe films were grown by molecular beam epitaxy (MBE) on GaAs and Corning glass substrates to investigate the characteristics of the films. Epitaxial growth of ZnTe was realized on GaAs substrates and a hole concentration of 8 × 1018 cm-3 with a resistivity of 0.045 Ω \\cdotcm was achieved as a result of nitrogen doping. In contrast, polycrystalline ZnTe films were grown on Corning glass and CdTe thin films. Dark and photoconductivity of ZnTe films increased to 1.43 × 10-5 S/cm and 1.41 × 10-4 S/cm, respectively, while the Zn to Te ratio was decreased to 0.25 during MBE growth. These ZnTe films with different thicknesses were inserted into close-spaced sublimation (CSS)-grown 1-μm-thick CdTe solar cells. A conversion efficiency of 8.31% (Voc: 0.74 V, Jsc: 22.98 mA/cm2, FF: 0.49, area: 0.5 cm2) was achieved for a 0.2-μm-thick ZnTe layer with a cell configuration of CdS/CdTe/ZnTe/Cu-doped-C/Ag. Furthermore, to overcome the problem of possible recombination loss in the interface layer of CdTe and ZnTe, the intermediate ternary CdZnTe is investigated. The compositional factor in Cd1-xZnxTe:N alloy is varied and the dependence of the conductivity is evaluated. For instance, Cd0.5Zn0.5Te:N, with dark and photoconductivity of 2.13 × 10-6 and 2.9 × 10-5 S/cm, respectively, is inserted at the back contact of a 1-μm-thick CdTe solar cell. A conversion efficiency of 7.46% (Voc: 0.68 V, Jsc: 22.60 mA/cm2, FF: 0.49, area: 0.086 cm2) was achieved as the primary result for a 0.2-μm-thick Cd0.5Zn0.5Te:N layer with the cell configuration of CdS/CdTe/Cd0.5Zn0.5Te:N/Au.

  15. Electrodeposited CdTe{emdash}optical properties

    Energy Technology Data Exchange (ETDEWEB)

    Rakhshani, A.E. [Physics Department, Kuwait University, PO Box 5969, Safat 13060 (Kuwait)

    1997-06-01

    For the measurement of optical constants, the electrodeposited films of CdTe were lifted off their opaque substrates and transferred onto glass slides using a transparent liquid adhesive. This technique proved to give results more reliable than those obtained on samples in which CdTe is deposited on CdS-coated conducting glass. The measured optical dispersion in the photon energy range of E{lt}1.5eV is in excellent agreement with that for the single crystal. The optical absorption coefficient was determined in the E{lt}3.5eV range and was compared with that for the single crystal. The results revealed two direct allowed transitions at 1.50 eV [{Gamma}{sub 8}valenceband(VB){r_arrow}{Gamma}{sub 6}conductionband(CB)] and 2.43 eV [{Gamma}{sub 7}(VB){r_arrow}{Gamma}{sub 6}(CB)] and three indirect allowed transitions at 1.27 eV [L{sub 4,5}(VB){r_arrow}{Gamma}{sub d}], 1.83 eV [L{sub 6}(VB){r_arrow}{Gamma}{sub d}], and 2.84 eV [{Gamma}{sub 8}(VB){r_arrow}L{sub 6}(CB)]. The 1.27 and the 1.83 eV transitions, which have not been reported previously and were not detected in single-crystal data, are attributed to the transitions to a grain-boundary-related defect energy band {Gamma}{sub d}, 0.65 eV above {Gamma}{sub 8} (VB). The indirect transitions at 1.83 and 2.84 eV are assisted by phonons having energies of 80 and 84 meV, respectively. {copyright} {ital 1997 American Institute of Physics.}

  16. Challenges and Prospects for Developing CdS/CdTe Substrate Solar Cells on Mo foils

    OpenAIRE

    Williams, Ben; Major, Jonathan; Bowen, Leon; Phillips, Laurie; Zoppi, Guillaume; Forbes, Ian; Durose, Ken

    2014-01-01

    ITO/ZnO/CdS/CdTe/Mo solar cells have been grown in the substrate configuration by a combination of close-space sublimation and RF sputtering. A peak efficiency of 8.01% was achieved. A two stage CdCl2 annealing process was developed, with the first stage contributing to CdTe doping and the second being linked to CdTe/CdS interdiffusion by secondary ion mass spectrometry analysis. The inclusion of a ZnO layer between CdS and ITO layers improved performance significantly (from η=6% to η=8%) by ...

  17. An ultrasensitive hydrogen peroxide biosensor based on electrocatalytic synergy of graphene-gold nanocomposite, CdTe-CdS core-shell quantum dots and gold nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Gu Zhiguo; Yang Shuping [School of Chemical and Material Engineering, Jiangnan University, Wuxi 214122 (China); Li Zaijun, E-mail: zaijunli@263.net [School of Chemical and Material Engineering, Jiangnan University, Wuxi 214122 (China); Sun Xiulan [School of Food Science and Technology, Jiangnan University, Wuxi 214122 (China); Wang Guangli [School of Chemical and Material Engineering, Jiangnan University, Wuxi 214122 (China); Fang Yinjun [Zhejiang Zanyu Technology Co., Ltd., Hangzhou 310009 (China); Liu Junkang [School of Chemical and Material Engineering, Jiangnan University, Wuxi 214122 (China)

    2011-09-02

    Graphical abstract: We first reported an ultrasensitive hydrogen peroxide biosensor in this work, which was fabricated by coating graphene-gold nanocomposite, CdTe-CdS core-shell quantum dots, gold nanoparticles and horseradish peroxidase in sequence on the surface of gold electrode. Since a promising their electrocatalytic synergy towards hydrogen peroxide was achieved, the biosensor displayed very high sensitivity, low detection limit (S/N = 3) (3.2 x 10{sup -11} M) and good long-term stability (20 weeks). Highlights: {center_dot} We for the first time integrated novel hydrogen peroxide biosensor based on G-AuNP, CdTe-CdS and AuNPs. {center_dot} Three nanomaterials show remarkable synergistic electrocatalysis towards hydrogen peroxide. {center_dot} The biosensor provides the best sensitivity in all biosensors based on graphene for detection of glucose up to now. - Abstract: We first reported an ultrasensitive hydrogen peroxide biosensor in this work. The biosensor was fabricated by coating graphene-gold nanocomposite (G-AuNP), CdTe-CdS core-shell quantum dots (CdTe-CdS), gold nanoparticles (AuNPs) and horseradish peroxidase (HRP) in sequence on the surface of gold electrode (GE). Cyclic voltammetry and differential pulse voltammetry were used to investigate electrochemical performances of the biosensor. Since promising electrocatalytic synergy of G-AuNP, CdTe-CdS and AuNPs towards hydrogen peroxide was achieved, the biosensor displayed a high sensitivity, low detection limit (S/N = 3) (3.2 x 10{sup -11} M), wide calibration range (from 1 x 10{sup -10} M to 1.2 x 10{sup -8} M) and good long-term stability (20 weeks). Moreover, the effects of omitting G-AuNP, CdTe-CdS and AuNP were also examined. It was found that sensitivity of the biosensor is more 11-fold better if G-AuNP, CdTe-CdS and AuNPs are used. This could be ascribed to improvement of the conductivity between graphene nanosheets in the G-AuNP due to introduction of the AuNPs, ultrafast charge transfer

  18. Response of Cds/CdTe Devices to Te Exposure of Back Contact: Preprint

    Energy Technology Data Exchange (ETDEWEB)

    Gessert, T. A.; Burst, J. M.; Ma, J.; Wei, S. H.; Kuciauskas, D.; Barnes, T. M.; Duenow, J. N.; Young, M. R.; Rance, W. L.; Li, J. V.; Dippo, P.

    2012-06-01

    Theoretical predictions of thin-film CdS/CdTe photovoltaic (PV) devices have suggested performance may be improved by reducing recombination due to Te-vacancy (VTe) or Te-interstitial (Tei) defects. Although formation of these intrinsic defects is likely influenced by CdTe deposition parameters, it also may be coupled to formation of beneficial cadmium vacancy (VCd) defects. If this is true, reducing potential effects of VTe or Tei may be difficult without also reducing the density of VCd. In contrast, post-deposition processes can sometimes afford a greater degree of defect control. Here we explore a post-deposition process that appears to influence the Te-related defects in polycrystalline CdTe. Specifically, we have exposed the CdTe surface to Te prior to ZnTe:Cu/Ti contact-interface formation with the goal of reducing VTe but without significantly reducing VCd. Initial results show that when this modified contact is used on a CdCl2-treated CdS/CdTe device, significantly poorer device performance results. This suggests two things: First, the amount of free-Te available during contact formation (either from chemical etching or CuTe or ZnTe deposition) may be a more important parameter to device performance than previously appreciated. Second, if processes have been used to reduce the effect of VTe (e.g., oxygen and chlorine additions to the CdTe), adding even a small amount of Te may produce detrimental defects.

  19. Misfit stress relaxation mechanism in CdTe(100) and CdTe/ZnTe(100) on a GaAs(100) highly mismatched heteroepitaxial layer

    Science.gov (United States)

    Nishino, H.; Sugiyama, I.; Nishijima, Y.

    1996-09-01

    We studied the misfit stress in CdTe(100)/GaAs(100). In general, this highly mismatched system initially forms a ``coincidence interface,'' where seven CdTe lattices match with eight GaAs lattices. In this system, the epilayer is elastically strained by the mismatch remaining between both groups of lattices. Afterward, the misfit stress is gradually relaxed with the generation of misfit dislocations. In this work, we derived a new model to describe this misfit relaxation mechanism and verified it with experimental observations. As introducing the effects of the interface modification, we found that the simple force balance between the substrate and epilayer governed the misfit stress. We assume that the relaxation process during growth is similar to that in CdTe/CdZnTe, since the residual misfit was fairly small. By extending the stress relaxation model of CdTe/GaAs, it is possible to explain the strain in CdTe/ZnTe/GaAs, which contains two highly mismatched interfaces. The threading dislocations in HgCdTe, derived from the CdTe buffer, decreased with increasing CdTe thickness. Assuming that the misfit dislocations are generated by bending threading dislocations, we could explain the dislocation reduction by utilizing the above misfit stress relaxation model. In spite of the extremely large mismatch, the structural quality of CdTe(100)/GaAs(100) was improved due to the relatively small strain remaining in the coincidence interface.

  20. Nitrogen Doped Zinc Telluride Back Contact to CdS/CdTe Solar Cells

    Science.gov (United States)

    Drayton, J.; Makhratchev, K.; Price, K. J.; Ma, X.; Simmons, D. A.; Ludwig, K.; Gupta, A.; Bohn, R. G.; Compaan, A. D.

    2000-10-01

    We describe the development of the Nitrogen doped ZnTe for the back contacts of CdS/CdTe solar cell. Reproducible p-ZnTe films were obtained using RF magnetron sputtering technique with Ar/N2 gas mixture. Both, intrinsic and nitrogen doped, ZnTe films were investigated for electronic properties. The conductivity of the N:ZnTe films was about five orders of magnitude higher than that of intrinsic ones. A bilayer of intrinsic and doped ZnTe films were used in back contact structure of CdS/CdTe solar cells. The ZnTe/N:ZnTe/Ni structure showed slightly lower initial performance but better stability in comparison to evaporated Cu/Au back contacts.

  1. C-V Calculations in CdS/CdTe Thin Films Solar Cells with a CdSxTe1-x Interlayer

    Directory of Open Access Journals (Sweden)

    A. Gonzalez-Cisneros

    2013-01-01

    Full Text Available In CdS/CdTe solar cells, chemical interdiffusion at the interface gives rise to the formation of an interlayer of the ternary compound CdSxCdTe1-x. In this work, we evaluate the effects of this interlayer in CdS/CdTe photovoltaic cells in order to improve theoretical results describing experimental C-V (capacitance versus voltage characteristics. We extended our previous theoretical methodology developed on the basis of three cardinal equations (Castillo-Alvarado et al., 2010. The present results provide a better fit to experimental data obtained from CdS/CdTe solar cells grown in our laboratory by the chemical bath deposition (for CdS film and the close-spaced vapor transport (for CdTe film techniques.

  2. Lattice sites of Li in CdTe

    NARCIS (Netherlands)

    Restle, M; BharuthRam, K; Quintel, H; Ronning, C; Hofsass, H; Wahl, U; Jahn, SG

    1996-01-01

    The lattice site occupation of Li in CdTe at temperatures between 40 and 500 K was investigated with the emission channeling method. Radioactive Li-8 ions were implanted at low doses into CdTe single crystals. Emission channeling patterns of alpha-particles emitted in the nuclear decay of Li-8 (t(1/

  3. Phase diagrams and microscopic structures of (Hg,Cd)Te, (Hg,Zn)Te, and (Cd,Zn)Te alloys

    Science.gov (United States)

    Patrick, R. S.; Chen, A.-B.; Sher, A.; Berding, M. A.

    1988-01-01

    A cluster theory based on the quasi-chemical approximation has been applied to study the local correlation bond-length distribution, and phase diagrams of the II-VI pseudobinary alloys Hg(1 - x)Cd(x)Te, Hg(1 - x)Zn(x)Te, and Cd(1 - x)Zn(x)Te. The cluster energy is calculated by letting it relax in some effective alloy medium and then considering the contributions from the strain and chemical energies. Two different models are presented to simulate the alloy medium. While both models show that all three alloys have nearly random distributions, the signs of the local correlation prove to be sensitive to the alloy medium chosen for the energy calculation. Good agreement is found between experiment and the bond lengths and phase diagrams in both models.

  4. Molecular beam epitaxy of CdTe and HgCdTe on large-area Si(100)

    Science.gov (United States)

    Sporken, R.; Lange, M. D.; Faurie, Jean-Pierre

    1991-09-01

    The current status of molecular beam epitaxy (MBE) of CdTe and HgCdTe on Si(100) is reviewed. CdTe and HgCdTe grow in the (111)B orientation on Si(100); monocrystalline films with two domains are obtained on most nominal Si(100) substrates, single domain films are grown on misoriented substrates and on nominal Si(100) preheated to 900-950 degree(s)C. Double-crystal x-ray rocking curves (DCRCs) with full-width at half-maximum (FWHM) as low as 110 arcsec are reported for HgCdTe on silicon; these layers are n-type, and electron mobilities higher than 5 X 104 cm2V-2s-1 are measured at 23 K for x equals 0.26. Excellent thickness and composition uniformity is obtained: standard deviation of the CdTe thickness 0.4% of the average thickness on 2-in. and 2.3% on 5-in., standard deviation of the Cd concentration in the HgCdTe layers 0.6% of the average concentration on 3-in. and 2.4% on 5-in. First results regarding growth of CdTe on patterned Si substrates are also reported.

  5. Development of high-efficiency, thin-film CdTe solar cells. Final subcontract report, 1 February 1992--30 November 1995

    Energy Technology Data Exchange (ETDEWEB)

    Rohatgi, A.; Chou, H.C.; Kamra, S.; Bhat, A. [Georgia Inst. of Tech., Atlanta, GA (United States)

    1996-01-01

    This report describes work performed by the Georgia Institute of Technology (GIT) to bring the polycrystalline CdTe cell efficiency a step closer to the practically achievable efficiency of 18% through fundamental understanding of detects and loss mechanisms, the role of chemical and heat treatments, and investigation of now process techniques. The objective was addressed by a combination of in-depth characterization, modeling, materials growth, device fabrication, and `transport analyses of Au/Cu/CdTe/CdS/SnO {sub 2} glass front-wall heterojunction solar cells. GiT attempted to understand the loss mechanism(s) in each layer and interface by a step-by-step investigation of this multilayer cell structure. The first step was to understand, quantify, and reduce the reflectance and photocurrent loss in polycrystalline CdTe solar calls. The second step involved the investigation of detects and loss mechanisms associated with the CdTe layer and the CdTe/CdS interface. The third stop was to investigate the effect of chemical and heat treatments on CdTe films and cells. The fourth step was to achieve a better and reliable contact to CdTe solar cells by improving the fundamental understanding. Of the effects of Cu on cell efficiency. Finally, the research involved the investigation of the effect of crystallinity and grain boundaries on Cu incorporation in the CdTe films, including the fabrication of CdTe solar calls with larger CdTe grain size.

  6. Synthesis of near-infrared-emitting CdTe/CdSe/ZnSe/ZnS heterostructure.

    Science.gov (United States)

    Yang, Ping

    2014-04-01

    Near-infrared-emitting quantum dots (QDs) were fabricated via organic synthesis strategies through constructing CdTe/CdSe/ZnSe/ZnS multishell heterostructure. An effective shell-coating route was developed for multishell growth on CdTe cores. Core/shell growth was monitored by absorption and photoluminescence (PL) spectroscopy and transmission electron microscopy observation. Yellow emitting CdTe cores were coated with a CdSe shell to generate type II structure. This yields core/shell QDs with red photoluminescence. The passivation by the ZnSe shell having a substantially wide bandgap confines the excitons within the CdTe/CdSe interface and isolates them from the solution environment and consequently improves the stability of the heterostructure. An additional ZnS shell was deposited around the outer layer of CdTe/CdSe/ZnSe QDs to form a heterostructure through the reaction between zinc oleate and trioctylphosphine sulfur in the crude CdTe/CdSe/ZnSe solution. By varying CdTe core size and each shell thickness, the PL wavelength of the obtained heterostructure can span from 580 to 770 nm. The PL efficiency is quenched in CdTe QDs in diluted solution but increases substantially up to 24% for CdTe/CdSe core/shell QDs. The PL efficiency of CdTe/CdSe/ZnSe/ZnS QDs with average diameter of 5.4 nm and a PL peak wavelength of 770 nm is 20%.

  7. Potentiality of photorefractive CdTe

    Energy Technology Data Exchange (ETDEWEB)

    Moisan, J.Y.; Gravey, P.; Picoli, G.; Wolffer, N.; Vieux, V. (Dept. Technologies Appliquees a la Connectique, Centre National d' Etudes des Telecommunications, 22 - Lannion (France))

    1993-01-30

    For optical telecommunication networks, optical switching is now being studied. Different solutions have been proposed (integrated optics, free space switching, etc.), and reconfigurable optical interconnects, based on phase conjugation, should be one interesting method. For example, some results have been obtained with a double-phase conjugated mirror configuration, allowing reconfigurable connection between single-mode optical fibres. These phase-conjugated optics use photorefractive crystals and the first demonstration has been given using Bi[sub 12]TiO[sub 20] photorefractive crystals. In a telecommunication network, semiconductive crystals with a good efficiency in the near-IR wavelength are needed. Our first experiments were carried out with InP:Fe crystals at 1.3 [mu]m. However, it is well known, from published studies, that II-VI materials are, in principle, more interesting for the following reasons. The electro-optic coefficient is higher (and therefore the figure of merit is higher). The solubility of dopants is higher (and therefore the space charge electric field, which modulates the refractive index of the material, may be higher). Next we tested a CdTe:V crystal and, in a two-wave mixing experiment without an external electric field, an amplification gain was observed and a high photosensitivity demonstrated at 1.3 [mu]m. In this paper, we shall describe the photorefractive effect and explain our choice of the CdTe:V crystal, taking into account the parameters of this photorefractive effect and some other parameters required by the applications in the optical beam steering field. Next the results will be given, and finally an optical configuration using phase conjugation will be presented as an example of application. (orig.).

  8. Development of Cd1-xMgxTe thin films for application as an electron reflector in CdS/CdTe solar cells

    Science.gov (United States)

    Kobyakov, Pavel S.

    Efficiencies of CdS/CdTe photovoltaic cells significantly lag behind their theoretical limit, primarily because open-circuit voltage ( VOC) of record efficiency cells (872 mV) is well below what is expected for the CdTe band gap (1.5 eV). A substantial V OC improvement can be achieved through addition of an electron reflector (ER) layer to CdTe devices. The ER layer forms a conduction-band barrier that reflects minority-charge carriers (i.e. electrons in p-type CdTe) away from the back surface. Similar to back-surface fields in c-Si, III-V, and CIGS solar cells, the ER strategy is expected to reduce back-surface recombination and is estimated to increase CdTe VOC by about 200 mV based on numerical simulation. The presented research investigates the addition of a thin layer of wider band gap Cd1-xMgxTe (CMT) to achieve a CdTe ER structure. First, a novel co-sublimation process was developed for deposition of Cd 1-xMgxTe thin films that demonstrates excellent experimental capabilities, commercial viability, and improved alloy control over other techniques. Next, the effects of processing on material properties of CMT deposition onto CdS/CdTe structures were investigated. It was discovered that substrate temperature during CMT deposition is a critical parameter for achieving uniform CMT film coverage on polycrystalline CdTe. Furthermore, CMT film growth was found to be epitaxial on CdTe where the CMT films retain the same microstructural features as the underlying CdTe grains. Despite film uniformity, significant Mg loss from the CMT film, oxide formation, and a reduction of the optical band gap was found after CdCl2-based passivation treatments. Preliminary process optimization found that band gap degradation can be minimized by utilizing MgCl2 in addition to CdCl2 as a treatment source material. Finally, development of CdS/CdTe/Cd1-xMgxTe electron reflector devices demonstrated a barrier behavior at high voltage bias and improved voltage when CdTe thickness is held

  9. CdS/CdTe interface analysis by transmission electron microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Dhere, R. G. [National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, Colorado 80401 (United States); Al-Jassim, M. M. [National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, Colorado 80401 (United States); Yan, Y. [National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, Colorado 80401 (United States); Jones, K. M. [National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, Colorado 80401 (United States); Moutinho, H. R. [National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, Colorado 80401 (United States); Gessert, T. A. [National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, Colorado 80401 (United States); Sheldon, P. [National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, Colorado 80401 (United States); Kazmerski, L. L. [National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, Colorado 80401 (United States)

    2000-07-01

    CdTe-based polycrystalline solar cells are leading candidates for terrestrial photovoltaic applications. High efficiency devices have been obtained despite large lattice mismatch between hexagonal CdS and cubic CdTe. In the present work, CdS was deposited by chemical bath deposition on Si substrates, and CdTe was deposited by close spaced sublimation. The chemical nature of the CdS/CdTe interface, structural properties, and their dependence on the fabrication parameters, e.g., substrate temperature (475-600 degree sign C) and postdeposition CdCl{sub 2} heat treatment, were analyzed. In addition, the effects of crystallinity of CdS on the interface structural defects were examined. Small spot energy dispersive spectroscopy of the interface revealed a considerable amount of sulfur in CdTe. The concentration of sulfur, in general, was higher in the grains with higher density of structural defects and at the grain boundaries. The planar defect density in CdTe films increased with substrate temperature, whereas the threading dislocation density decreased. Interface analysis showed that the majority of the crystalline defects in the CdTe films deposited on CdS were generated at the interface. The crystallinity of CdS did not have a major influence on the interface defect generation. (c) 2000 American Vacuum Society.

  10. Synthesis and Spectral Studies of CdTe-Dendrimer Conjugates

    Science.gov (United States)

    Ghosh, Srabanti; Saha, Abhijit

    2009-08-01

    In order to couple high cellular uptake and target specificity of dendrimer molecule with excellent optical properties of semiconductor nanoparticles, the interaction of cysteine-capped CdTe quantum dots with dendrimer was investigated through spectroscopic techniques. NH2-terminated dendrimer molecule quenched the photoluminescence of CdTe quantum dots. The binding constants and binding capacity were calculated, and the nature of binding was found to be noncovalent. Significant decrease in luminescence intensity of CdTe quantum dots owing to noncovalent binding with dendrimer limits further utilization of these nanoassemblies. Hence, an attempt is made, for the first time, to synthesize stable, highly luminescent, covalently linked CdTe-Dendrimer conjugate in aqueous medium using glutaric dialdehyde (G) linker. Conjugate has been characterized through Fourier transform infrared spectroscopy and transmission electron microscopy. In this strategy, photoluminescence quantum efficiency of CdTe quantum dots with narrow emission bandwidths remained unaffected after formation of the conjugate.

  11. Herstellung von CdTe-Dünnschichtsolarzellen bei reduzierten Abscheidetemperaturen

    OpenAIRE

    Schaffner, Judith

    2012-01-01

    CdTe ist ein sehr aussichtsreiches Absorbermaterial für Dünnschichtsolarzellen. Mit CdTe-Solarzellen wurden bereits Wirkungsgrade bis zu 17,3% erzielt. Die CdS und CdTe Schichten für diese Solarzellen können mit den verschiedensten Abscheidetechniken, wie Sputtern, Chemische Badabscheidung (CVD), Druckverfahren, Hochvakuumverdampfen (HVE) und Close Space Sublimation (CSS) hergestellt werden. Hohe Durchsätze machen CSS zu einer attraktiven Methode für die industrielle Großproduktion. Um mit...

  12. Factors Influencing Photoluminescence and Photocarrier Lifetime in CdSeTe/CdMgTe Double Heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Swartz, C. H.; Zaunbrecher, Katherine N.; Sohal, S.; LeBlanc, E. G.; Edirisooriya, M.; Ogedengbe, O. S.; Petersen, J. E.; Jayathilaka, P. A. R. D.; Myers, T. H.; Holtz, M. W.; Barnes, Teresa M.

    2016-10-28

    CdSeTe/CdMgTe double heterostructures were produced with both n-type and unintentionally doped absorber layers. Measurements of the dependence of photoluminescence intensity on excitation intensity were carried out, as well as measurements of time-resolved photoluminescence decay after an excitation pulse. It was found that decay times under very low photon injection conditions are dominated by a non-radiative Shockley-Read-Hall process described using a recombination center with an asymmetric capture cross section, where the cross section for holes is larger than that for electrons. As a result of the asymmetry, the center effectively extends photoluminescence decay by a hole trapping phenomenon. A reduction in electron capture cross section appeared at doping densities over 10^16cm-3. An analysis of the excitation intensity dependence of room temperature photoluminescence revealed a strong relationship with doping concentration. This allows estimates of the carrier concentration to be made through a non-destructive optical method. Iodine was found to be an effective n-type dopant for CdTe, allowing controllable carrier concentrations without an increased rate of non-radiative recombination.

  13. Growth of CdTe: Al films; Crecimiento de peliculas de CdTe: Al

    Energy Technology Data Exchange (ETDEWEB)

    Gonzalez A, M.; Zapata T, M. [CICATA-IPN, 89600 Altamira, Tamaulipas (Mexico); Melendez L, M. [CINVESTAV-IPN, A.P. 14-740, 07000 Mexico D.F. (Mexico); Pena, J.L. [CINVESTAV-IPN, A.P. 73 Cordemex, 97310 Merida, Yucatan (Mexico)

    2006-07-01

    CdTe: AI films were grown by the close space vapor transport technique combined with free evaporation (CSVT-FE). The Aluminum (Al) evaporation was made by two kinds of sources: one made of graphite and the other of tantalum. The films were deposited on glass substrates. The Al source temperature was varied maintaining the CdTe source temperature fixed as well as the substrate temperature. The films were characterized by x-ray energy dispersive analysis (EDAX), x-ray diffraction and optical transmission. The results showed for the films grown with the graphite source for Al evaporation, the Al did not incorporate in the CdTe matrix, at least to the level of EDAX sensitivity; they maintained the same crystal structure and band gap. For the samples grown with the tantalum source, we were able to incorporate the Al. The x-ray diffraction patterns show that the films have a crystal structure that depends on Al concentration. They were cubic up to 2.16 at. % Al concentration; for 19.65 at. % we found a mixed phase; for Al concentration higher than 21 at. % the films were amorphous. For samples with cubic structure it was found that the lattice parameter decreases and the band gap increases with Al concentration. (Author)

  14. Comparative study of electrical properties of Cd and Te-enriched CdTe thin films at cryogenic temperature

    Energy Technology Data Exchange (ETDEWEB)

    Shah, Nazar Abbas, E-mail: nabbasqureshi@yahoo.co [Thin Films Research Laboratory, Department of Physics, COMSATS Institute of Information Technology, Park Road, Islamabad 45320 (Pakistan)

    2010-09-17

    Cd and Te-enriched cadmium telluride (CdTe) polycrystalline thin films were grown on corning glass substrates by Close Spaced Sublimation (CSS) technique. The structural investigations performed by means of X-ray diffraction (XRD) technique, scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDX) showed that the deposited films exhibit a polycrystalline structure with <1 1 1> as preferred orientation. The optical transmittance for Te-enriched CdTe sample was above 0.8 in the range of 1500-2500 nm, which was significantly below 0.8 for Cd-enriched CdTe sample. The electrical properties of these samples were analyzed as a function of the Cd and Te concentration at cryogenic temperature. The electrical resistivity dropped several orders of magnitude. These properties are significantly changed at cryogenic temperature. The comparative study revealed that using this deposition technique, n-type, and p-type Cd and Te-enriched CdTe polycrystalline films can be produced.

  15. Isothermal close space sublimation of CdTe/ZnTe heterostructures in vacuum conditions

    Energy Technology Data Exchange (ETDEWEB)

    Melo, O. de; Garcia, B.J. [Departamento de Fisica Aplicada, Universidad Autonoma de Madrid. Cantoblanco 28049, Madrid (Spain); Sanchez, M. [Physics Faculty, IMRE, University of Havana, Colina Universitaria, 10400 La Habana (Cuba); Departamento de Fisica Aplicada, Universidad Autonoma de Madrid. Cantoblanco 28049, Madrid (Spain); Hernandez-Velez, M. [Departamento de Fisica Aplicada, Universidad Autonoma de Madrid. Cantoblanco 28049, Madrid (Spain); Unidad GMNF Asociada al CSIC, Cantoblanco 28049, Madrid (Spain)

    2010-06-15

    Thin films and structures of ZnTe and CdTe have been grown by isothermal close space sublimation using alternated exposure of single crystalline substrates to elemental Zn, Te and Cd sources. The results show that the use of vacuum conditions promotes the transport of vapors towards the surface and then efficient growth at lower temperatures. Films thickness ranged between 200 and 600 nm for 50 cycles samples. ZnTe and CdTe films were obtained even at temperatures as low as 310 C. This is important because low temperatures worsen the inter- diffusion processes; as a consequence we have obtained relatively abrupt interfaces in the ZnTe/CdTe system. Its compositional, structural and optical properties are presented. These results offer new possibilities of this low cost technique for growing heterostructures. (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  16. Rf sputtering of CdTE and CdS for thin film PV

    Energy Technology Data Exchange (ETDEWEB)

    Compaan, A.D.; Tabory, C.N.; Shao, M.; Fischer, A.; Feng, Z.; Bohn, R.G. (Department of Physics and Astronomy, University of Toledo, Toledo, Ohio 43606 (United States))

    1994-06-30

    In late 1992 we demonstrated the first rf sputtered CdS/CdTe photovoltaic cell with efficiency exceeding 10%. In this cell both CdS and CdTe layers were deposited by rf sputtering. In this paper we report preliminary measurements of (1) optical emission spectroscopy of the rf plasma, (2) the width of the phonon Raman line as a function of deposition temperature for CdS, and (3) studies of oxygen doping during pulsed laser deposition of CdTe.

  17. Achievements and Challenges of CdS/CdTe Solar Cells

    Directory of Open Access Journals (Sweden)

    Zhou Fang

    2011-01-01

    Full Text Available Thin film CdS/CdTe has long been regarded as one promising choice for the development of cost-effective and reliable solar cells. Efficiency as high as 16.5% has been achieved in CdS/CdTe heterojunction structure in laboratory in 2001, and current techniques for CdS/CdTe solar cells gradually step toward commercialization. This paper reviews some novel techniques mainly within two years to solve this problem from aspects of promotion of fabrication technology, structural modification, and choice of back contact materials.

  18. Achievements and Challenges of CdS/CdTe Solar Cells

    OpenAIRE

    Zhou Fang; Xiao Chen Wang; Hong Cai Wu; Ce Zhou Zhao

    2011-01-01

    Thin film CdS/CdTe has long been regarded as one promising choice for the development of cost-effective and reliable solar cells. Efficiency as high as 16.5% has been achieved in CdS/CdTe heterojunction structure in laboratory in 2001, and current techniques for CdS/CdTe solar cells gradually step toward commercialization. This paper reviews some novel techniques mainly within two years to solve this problem from aspects of promotion of fabrication technology, structural modification, and cho...

  19. Raman characterization of a new Te-rich binary compound: CdTe2.

    Science.gov (United States)

    Rousset, Jean; Rzepka, Edouard; Lincot, Daniel

    2009-04-02

    Structural characterization by Raman spectroscopy of CdTe thin films electrodeposited in acidic conditions is considered in this work. This study focuses on the evolution of material properties as a function of the applied potential and the film thickness, demonstrating the possibility to obtain a new Te-rich compound with a II/VI ratio of 1/2 under specific bath conditions. Raman measurements carried out on etched samples first allow the elimination of the assumption of a mixture of phases CdTe + Te and tend to confirm the formation of the CdTe(2) binary compound. The signature of this phase on the Raman spectrum is the increase of the LO band intensity compared to that obtained for the CdTe. The influence of the laser power is also considered. While no effect is observed on CdTe films, the increase of the incident irradiation power leads to the decomposition of the CdTe(2) compound into two more stable phases namely CdTe and Te.

  20. Radiative and interfacial recombination in CdTe heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Swartz, C. H., E-mail: craig.swartz@txstate.edu; Edirisooriya, M.; LeBlanc, E. G.; Noriega, O. C.; Jayathilaka, P. A. R. D.; Ogedengbe, O. S.; Hancock, B. L.; Holtz, M.; Myers, T. H. [Materials Science, Engineering, and Commercialization Program, Texas State University, 601 University Dr., San Marcos, Texas 78666 (United States); Zaunbrecher, K. N. [National Renewable Energy Laboratory, 15013 Denver West Parkway, Mississippi RSF200, Golden, Colorado 80401 (United States)

    2014-12-01

    Double heterostructures (DH) were produced consisting of a CdTe film between two wide band gap barriers of CdMgTe alloy. A combined method was developed to quantify radiative and non-radiative recombination rates by examining the dependence of photoluminescence (PL) on both excitation intensity and time. The measured PL characteristics, and the interface state density extracted by modeling, indicate that the radiative efficiency of CdMgTe/CdTe DHs is comparable to that of AlGaAs/GaAs DHs, with interface state densities in the low 10{sup 10 }cm{sup −2} and carrier lifetimes as long as 240 ns. The radiative recombination coefficient of CdTe is found to be near 10{sup −10} cm{sup 3}s{sup −1}. CdTe film growth on bulk CdTe substrates resulted in a homoepitaxial interface layer with a high non-radiative recombination rate.

  1. Optical modeling of graphene contacted CdTe solar cells

    Science.gov (United States)

    Aldosari, Marouf; Sohrabpoor, Hamed; Gorji, Nima E.

    2016-04-01

    For the first time, an optical model is applied on CdS/CdTe thin film solar cells with graphene front or back contact. Graphene is highly conductive and is as thin as a single atom which reduces the light reflection and absorption, and thus enhances the light transmission to CdTe layer for a wide range of wavelengths including IR. Graphene as front electrode of CdTe devices led to loss in short circuit current density of 10% ΔJsc ≤ 15% compared to the conventional electrodes of TCO and ITO at CdS thickness of dCdS = 100 nm. In addition, all the multilayer graphene electrodes with 2, 4, and 7 graphene layers led to Jsc ≤ 20 mA/cm2. Therefore, we conclude that a single monolayer graphene with hexagonal carbon network reduces optical losses and enhances the carrier collection measured as Jsc. In another structure design, we applied the optical model to graphene back contacted CdS/CdTe device. This scheme allows double side irradiation of the cell which is expected to enhance the Jsc. We obtained 1 ∼ 6 , 23, and 38 mA/cm2 for back, front and bifacial illumination of graphene contacted CdTe cell with CdS = 100 nm. The bifacial irradiated cell, to be efficient, requires an ultrathin CdTe film with dCdTe ≤ 1 μm. In this case, the junction electric field extends to the back region and collects out the generated carriers efficiently. This was modelled by absorptivity rather than transmission rate and optical losses. Since the literature suggest that ZnO can increase the graphene conductivity and enhance the Jsc, we performed our simulations for a graphene/ZnO electrode (ZnO = 100 nm) instead of a single graphene layer.

  2. Photoluminescence study of Cu diffusion in CdTe

    Energy Technology Data Exchange (ETDEWEB)

    Grecu, D.; Compaan, A.D. [Department of Physics, University of Toledo, Toledo, Ohio (United States)

    1999-03-01

    We report changes in the photoluminescence spectra associated with the diffusion of Cu in CdTe thin films used in CdTe/CdS solar cells. Films grown by vapor transport deposition and radio-frequency sputtering as well as single crystal CdTe were included in the study. The main effects of Cu diffusion appear to be the quenching of a donor-acceptor transition associated with Cd vacancies and the increase in intensity of a lower energy broad-band transition. The PL is subsequently used to explore the effects of electric fields on Cu diffusion. The role of Te as a diffusion barrier for Cu is investigated. {copyright} {ital 1999 American Institute of Physics.}

  3. An NMR quantum computer of the semiconductor CdTe

    Science.gov (United States)

    Shimizu, T.; Goto, A.; Hashi, K.; Ohki, S.

    2002-12-01

    We propose a method to implement a quantum computer by solid-state NMR. We can use the J-coupling for the quantum gate in CdTe. Both Cd and Te have two isotopes with spin 1/2, then we can have 4-qubits. The decoherence by dipole interaction may be minimized by preparing the isotope superlattice grown in the order of— 111Cd- 123Te- 113Cd- 125Te—in the [111] direction and by applying the magnetic field in the direction of [100], the magic angle of the dipole interaction. The optical pumping technique can be used in CdTe to make the initialization of the qubits.

  4. CdTe Photovoltaics for Sustainable Electricity Generation

    Science.gov (United States)

    Munshi, Amit; Sampath, Walajabad

    2016-09-01

    Thin film CdTe (cadmium telluride) is an important technology in the development of sustainable and affordable electricity generation. More than 10 GW of installations have been carried out using this technology around the globe. It has been demonstrated as a sustainable, green, renewable, affordable and abundant source of electricity. An advanced sublimation tool has been developed that allows highly controlled deposition of CdTe films onto commercial soda lime glass substrates. All deposition and treatment steps can be performed without breaking the vacuum within a single chamber in an inline process that can be conveniently scaled to a commercial process. In addition, an advanced cosublimation source has been developed to allow the deposition of ternary alloys such as Cd x Mg1- x Te to form an electron reflector layer which is expected to address the voltage deficits in current CdTe devices and to achieve very high efficiency. Extensive materials characterization, including but not limited to scanning electron microscopy, transmission electron microscopy, energy dispersive x-ray spectroscopy, high resolution transmission electron microscopy and electron back-scatter diffraction, has been performed to get a better understanding of the effects of processing conditions on CdTe thin film photovoltaics. This combined with computer modeling such as density function theory modeling gives a new insight into the mechanism of CdTe photovoltaic function. With all these efforts, CdTe photovoltaics has seen great progress in the last few years. Currently, it has been recorded as the cheapest source of electricity in the USA on a commercial scale, and further improvements are predicted to further reduce the cost while increasing its utilization. Here, we give an overview of the advantages of thin film CdTe photovoltaics as well as a brief review of the challenges that need to be addressed. Some fundamental studies of processing conditions for thin film CdTe are also presented

  5. The morphology, microstructure, and luminescent properties of CdS/CdTe films

    Energy Technology Data Exchange (ETDEWEB)

    Al-Jassim, M.M.; Dhere, R.G.; Jones, K.M.; Hasoon, F.S.; Sheldon, P. [National Renewable Energy Lab., Golden, CO (United States)

    1998-09-01

    This paper is concerned with the characterization of CdS/CdTe polycrystalline thin films for solar cells. The morphology, microstructure, and luminescent properties are studied by a powerful array of characterization techniques. The presence of pinholes in 100-nm thick CdS is observed. The microstructure of CdS and CdTe films is shown to be heavily faulted polycrystalline. The effect of deposition temperature on the grain size and the microstructure is investigated. The interdiffusion of sulfur and tellurium at the CdS/CdTe interface is studied for the first time by a nanoprobe technique. Considerable amount of sulfur is detected in CdTe in the vicinity of the interface of samples deposited at 625 C. The recombination behavior of grain boundaries and intragrain defects is investigated in as-deposited and heat-treated samples.

  6. Flexible CdTe/CdS solar cells on thin glass substrates.

    Science.gov (United States)

    Seo, Won-Oh; Kim, Donghwan; Kim, Jihyun

    2015-04-06

    We demonstrate flexible CdTe/CdS thin-film solar cells in a superstrate configuration with a cell conversion efficiency as high as 10.9%. We deposit a CdS window layer and a CdTe absorber layer on a flexible glass substrate using the chemical bath deposition method and close-spaced sublimation method, respectively. The thin and flexible glass substrates were able to tolerate a high growth temperature and post-growth processes. We repeatedly apply a strain of 0.15% to the fabricated CdTe/CdS solar cells, and this was shown to have a negligible effect on their performances. Our proposed thin films-on-compliant substrate structure, which was prepared by replacing a rigid glass with a bendable one, demonstrated flexible CdTe/CdS p-n junction thin-film solar cells without compromising the cell performance.

  7. Research on Cu2ZnSnTe4 crystals and heterojunctions based on such crystals

    Directory of Open Access Journals (Sweden)

    Kovaliuk T. T.

    2015-12-01

    Full Text Available The paper reports on the results of the studies of magnetic, kinetic and optical properties of Cu2ZnSnTe4 crystals. The Cu2ZnSnTe4 crystals showed diamagnetic properties (the magnetic susceptibility almost independent of the magnetic field and temperature. The Cu2ZnSnTe4 crystals possessed p-type of conductivity and the Hall coefficient was independent on temperature. The temperature dependence of the electrical conductivity of the Cu2ZnSnTe4 crystal shows metallic character, i. e. decreases with the increase of temperature, that is caused by the lower charge carrier mobility at higher temperature. Thermoelectric power of the samples ispositive that also indicates on the prevalence of p-type conductivity. Heterojunctions n-TiN/p-Cu2ZnSnTe4, n-TiO2/p-Cu2ZnSnTe4 and n-MoO/p-Cu2ZnSnTe4 were fabricated by the reactive magnetron sputtering of TiN, TiO2 and MoOx thin films, respectively, onto the substrates made of the Cu2ZnSnTe4 crystals. The dominating current transport mechanisms in the n-TiN/p-Cu2ZnSnTe4 and n-TiO2/p-Cu2ZnSnTe4 heterojunctions were established to be the tunnel-recombination mechanism at forward bias and tunneling at reverse bias.

  8. An investigation for the HgCdTe cleaning process

    Science.gov (United States)

    Lan, Tian-Yi; Wang, Nili; Zhao, Shuiping; Liu, Shi-Jia; Li, Xiang-Yang

    2014-11-01

    A new cleaning process for HgCdTe was designed - which used the improved SC-1,SC-2 and Br2- C2H5OH solutions as the main cleaning fluid and applied mega sound waves in the cleaning process. By analyzing the test results carried out on the HgCdTe surface, it was found that the material of HgCdTe for the application of new cleaning process was better than the one for the application of conventional cleaning process in the minority carrier lifetime, residual organic contamination, responsivity and specific detectivity.

  9. Process Development for High Voc CdTe Solar Cells

    Energy Technology Data Exchange (ETDEWEB)

    Ferekides, C. S.; Morel, D. L.

    2011-05-01

    This is a cumulative and final report for Phases I, II and III of this NREL funded project (subcontract # XXL-5-44205-10). The main research activities of this project focused on the open-circuit voltage of the CdTe thin film solar cells. Although, thin film CdTe continues to be one of the leading materials for large-scale cost-effective production of photovoltaics, the efficiency of the CdTe solar cells have been stagnant for the last few years. This report describes and summarizes the results for this 3-year research project.

  10. The rotational spectra, potential function, Born-Oppenheimer breakdown, and magnetic shielding of SnSe and SnTe.

    Science.gov (United States)

    Bizzocchi, Luca; Giuliano, Barbara M; Hess, Mareike; Grabow, Jens-Uwe

    2007-03-21

    The pure rotational spectra of 27 isotopic species of SnSe and SnTe have been measured in the frequency range of 5-24 GHz using a Fabry-Perot-type resonator pulsed-jet Fourier-transform microwave spectrometer. Gaseous samples of both chalcogenides were prepared by laser ablation of suitable target rods and were stabilized in supersonic jets of Ar. Global multi-isotopolog analyses of all available high-resolution data produced spectroscopic Dunham parameters Y01, Y11, Y21, Y31, Y02, and Y12 for both species, as well as Born-Oppenheimer breakdown (BOB) coefficients delta01 for Sn, Se, and Te. A direct fit of the same data sets to an appropriate radial Hamiltonian yielded analytic potential energy functions and BOB radial functions for the X 1Sigma+ electronic state of both SnSe and SnTe. Additionally, the magnetic hyperfine interaction produced by the dipolar nuclei 119Sn, 117Sn, 77Se, and 125Te was observed, yielding first determinations of the corresponding spin-rotation coupling constants.

  11. Effect of Intermixing at CdS/CdTe Interface on Defect Properties

    Energy Technology Data Exchange (ETDEWEB)

    Park, Ji-Sang; Yang, Ji-Hui; Barnes, Teresa; Wei, Su-Huai

    2016-07-25

    We investigated the stability and electronic properties of defects in CdTe 1- xSx that can be formed at the CdS/CdTe interface. As the anions mix at the interface, the defect properties are significantly affected, especially those defects centered at cation sites like Cd vacancy, VCd, and Te on Cd antisite, TeCd, because the environment surrounding the defect sites can have different configurations. We show that at a given composition, the transition energy levels of VCd and TeCd become close to the valence band maximum when the defect has more S atoms in their local environment, thus improving the device performance. Such beneficial role is also found at the grain boundaries when the Te atom is replaced by S in the Te-Te wrong bonds, reducing the energy of the grain boundary level. On the other hand, the transition levels with respect to the valence band edge of CdTe 1- xSx increases with the S concentration as the valence band edge decreases with the S concentration, resulting in the reduced p-type doping efficiency.

  12. Simulation of the Efficiency of CdS/CdTe Tandem Multi-Junction Solar Cells

    CERN Document Server

    Mirkamali, Ashrafalsadat S

    2016-01-01

    In this paper we study CdS/CdTe solar cells by means of AMPS-1D software. First we study the effect of thickness of semiconductor layers on the output parameters of the CdS/CdTe solar cell, such as density of short-circuit current, open circuit voltage, fill factor and efficiency. Numerical simulation shows that the highest efficiency of single-junction CdS/CdTe solar cell equal to 18.3% is achieved when the CdTe layer thickness is 1000 nm and a CdS layer is 60 nm. Then, in order to obtain the maximal value of the efficiency, new tandem multi-junction structure consisting of layers of two solar cells connected with each other back to back are designed and engineered taking into account the results obtained for the single-junction solar cells. Numerical simulations show that its highest efficiency in 31.8% can be obtained when the thickness of CdS p-layer is equal to 50 nm, and the thickness of the CdS n-layer is equal to 200 nm, while thicknesses of the CdTe n-layer and CdTe p-layer are kept fixed and equal t...

  13. Contacts for high-resistivity (Cd,Mn)Te crystals

    Energy Technology Data Exchange (ETDEWEB)

    Witkowska-Baran, M.; James, R.; Mycielski, A.; Kochanowska, D.; Szadkowski, A.J.; Jakiela, R.; Witkowska, B.; Kaliszek, W.; Domagala, J.; Lusakowska, E.; Domukhovski, V.; Dybko, K.; Cui, Y.; and James, R.B.

    2010-09-09

    Semi-insulating (Cd,Mn)Te crystals offer a material that may compete well with the commonly used (Cd,Zn)Te crystals for manufacturing large-area X- and gamma-ray detectors. The Bridgman growth method yields good quality, high-resistivity (10{sup 9} - 10{sup 10} {Omega} {center_dot} cm) crystals of (Cd,Mn)Te:V. Doping the as-grown crystals with the compensating agent vanadium ({approx} 10{sup 16} cm{sup -3}) ensures their high resistivity; thereafter, annealing them in cadmium vapors reduces the number of cadmium vacancies. Applying the crystals as detectors necessitates having satisfactory electrical contacts. Accordingly, we explored various techniques of ensuring good electrical contacts to these semi-insulating (Cd,Mn)Te crystals, assessing metallic layers, monocrystalline semiconductor layers, and amorphous (or nanocrystalline) semiconductor layers. We found that ZnTe heavily doped ({approx} 10{sup 18} cm{sup -3}) with Sb, and CdTe heavily doped ({approx} 10{sup 17} cm{sup -3}) with In, proved satisfactory semiconductor contact layers. They subsequently enabled us to establish good contacts (with only narrow tunneling barriers) to the Au layer that usually constitutes the most external contact layer. We outline our technology of applying electrical contacts to semi-insulating (Cd,Mn)Te, and describe some important properties.

  14. Preparation and properties of evaporated CdTe films

    Science.gov (United States)

    Bube, R. H.; Fahrenbruch, A. L.; Chien, K. F.

    1987-07-01

    Previous work on evaporated CdTe films for photovoltaics showed no clear path to successful p-type doping of CdTe during deposition. Post-deposition annealing of the films in various ambients thus was examined as a means of doping. Anneals were done in Te, Cd, P, and As vapors and in vacuum, air and Ar, all of which showed large effects on series resistance and diode parameters. With As, series resistance values of In/p-CdTe/graphite structures decreased markedly. This decrease was due to a decrease in grain boundary and/or back contact barrier height, and thus was due to large increases in mobility; the carrier density was not altered substantially. Although the series-resistance decreases were substantial, the diode characteristics became worse. The decreases were not observed when CdS/CdTe cells were fabricated on Te vapor-annealed films. Preparation of ZnO films by reactive evaporation yielded promising results. Deposition of p-ZnTe films by hot-wall vapor evaporation, using conventional techniques, yielded acceptable specimens.

  15. Facile method to prepare CdS nanostructure based on the CdTe films

    Energy Technology Data Exchange (ETDEWEB)

    Ma, Ligang; Chen, Yuehui; Wei, Zelu; Cai, Hongling; Zhang, Fengming; Wu, Xiaoshan, E-mail: xswu@nju.edu.cn

    2015-09-15

    Graphical abstract: - Highlights: • CdS nanostructure is directly fabricated on CdTe film only by heating treatment under H{sub 2}S/N{sub 2} mixed atmosphere at a relatively low temperature (450 °C) with gold layer as the intermediate. • Nanostructure of CdS layer, varying from nanowires to nanosheets, may be controlled by the thickness of gold film. • The change of morphology adjusts its luminescence properties. - Abstract: Nanostructured cadmium sulfide (CdS) plays critical roles in electronics and optoelectronics. In this paper, we report a method to fabricate CdS nanostructure directly on CdTe film, via a thermal annealing method in H{sub 2}S/N{sub 2} mixed gas flow at a relatively low temperature (450 °C). The microstructure and optical properties of CdS nanostructure are investigated by X-ray diffraction, transmission electron microscopy, Raman, and photoluminescence. The morphology of CdS nanostructure, evolving from nanowires to nanosheets, can be controlled by the thickness of Au film deposited on the CdTe film. And CdS nanostructures are single crystalline with the hexagonal wurtzite structure. Raman spectroscopy under varying the excitation wavelengths confirm that synthesized CdS-CdTe films contain two layers, i.e., CdS nanostructure (top) and CdTe layer (bottom). The change of morphology modifies its luminescence properties. Obviously, through simply thermal annealing in H{sub 2}S/N{sub 2} mixed gas, fabricating CdS nanostructure on CdTe film can open up the new possibility for obtaining high efficient CdTe solar cell.

  16. Insulators for Pb(1-x)Sn(x)Te

    Science.gov (United States)

    Tsuo, Y. H.; Sher, A.

    1981-01-01

    Thin films of LaF3 were e-gun and thermally deposited on several substrates. The e-gun deposited films are fluorine deficient, have high ionic conductivities that persist to 77 K, and high effective dielectric constants. The thermally deposited material tends to be closer to stoichiometric, and have higher effective breakdown field strengths. Thermally deposited LaF3 films with resistivities in excess of 10 to the 12th power ohms - cm were deposited on metal coated glass substrates. The LaF3 films were shown to adhere well to PbSnTe, surviving repeated cycles between room temperature and 77 K. The LaF3 films on GaAs were also studied.

  17. Thin film CdS/CdTe solar cells: Research perspectives

    Energy Technology Data Exchange (ETDEWEB)

    Morales-Acevedo, Arturo [CINVESTAV del IPN, Department of Electrical Engineering, Avenida IPN No. 2508, 07360 Mexico DF (Mexico)

    2006-06-15

    Polycrystalline thin film CdTe continues to be a leading material for the development of cost effective and reliable photovoltaics. The two key properties of this material are its band gap (1.5eV), close to the ideal for photovoltaic conversion efficiency (1.45eV), and its high optical absorption coefficient. Thin film CdTe solar cells are typically hetero-junctions with CdS being the n-type partner, or window layer. Efficiencies as high as 16.5% have been achieved, but still there is some potential for increasing them. We make an analysis of the typical CdS/CdTe superstrate solar cell, and from it we establish critical issues and different lines of research in order to improve the current efficiencies. We also show that present record efficiencies are very close to the practical efficiency limit for a CdS/CdTe hetero-junction cell. (author)

  18. Growth and optical investigations of high quality individual CdTe/(Cd,Mg)Te core/shell nanowires

    Science.gov (United States)

    Wojnar, P.; Płachta, J.; Kret, S.; Kaleta, A.; Zaleszczyk, W.; Szymura, M.; Wiater, M.; Baczewski, L. T.; Pietruczik, A.; Karczewski, G.; Wojtowicz, T.; Kossut, J.

    2017-01-01

    CdTe nanowires with the average diameter of only 40 nm coated with (Cd,Mg)Te shells are grown using Au-catalyzed vapor-liquid-solid growth mechanism in a system for molecular beam epitaxy. High optical quality of individual nanowires is revealed by means of low temperature cathodoluminescence and micro-luminescence. It is found that, the optical emission spectrum consists mostly of the near band edge emission without any significant contribution of defect related luminescence. Moreover, the importance of surface passivation with (Cd,Mg)Te coating shells is demonstrated.

  19. Study of Back Contacts for CdTe Solar Cells

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    ZnTe/ZnTe∶Cu layer is used as a complex back contact. The parameters of CdTe solar cells with and without the complex back contacts are compared. The effects of un-doped layer thickness, doped concentration and post-deposition annealing temperature of the complex layer on solar cells performance are investigated.The results show that ZnTe/ZnTe∶Cu layer can improve back contacts and largely increase the conversion efficiency of CdTe solar cells. Un-doped layer and post-deposition annealing of high temperature can increase open voltage. Using the complex back contact, a small CdTe cell with fill factor of 73.14% and conversion efficiency of 12.93% is obtained.

  20. 13.4% efficient thin-film CdS/CdTe solar cells

    Science.gov (United States)

    Chu, T. L.; Chu, S. S.; Ferekides, C.; Wu, C. Q.; Britt, J.; Wang, C.

    1991-12-01

    Cadmium telluride is a promising thin-film photovoltaic material as shown by the more than 10% efficient CdS/CdTe heterojunction solar cells. In this work, thin-film CdS/CdTe solar cells have been prepared using CdS films grown from an aqueous solution and p-CdTe films deposited by close-spaced sublimation (CSS). The properties of CdS films deposited from an ammonical solution of a Cd-salt, an ammonium salt, and thiourea have been controlled by optimizing the temperature and composition of the solution. The solution-grown CdS films have a high photoconductivity ratio, and its optical transmission is superior to that of vacuum evaporated CdS films. The properties of p-CdTe films deposited by CSS have been optimized by controlling the temperature and composition of the source material, and the substrate temperature. The properties of CdS/CdTe heterojunctions have been studied; junction photovoltage spectroscopy is used for the qualitative comparison of junction characteristics. Solar cells of 1-cm2 area with an AM 1.5 efficiency of 13.4% are reported.

  1. X and {gamma}-Ray imaging CdTe/CdZnTe detectors. From material to imaging; Imagerie X et {gamma}. Detecteurs CdTe/CdZnTe. Du materiau a l'imageur

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1999-07-01

    This document presents the recent advances made by the Laboratory of electronics and computer science technologies (Leti) of the French atomic energy commission (CEA) in the domain of semiconductor detectors for X- and {gamma}-ray imaging systems. The new generation of detectors is based on the use of cadmium telluride CdTe or its compound CdZnTe, in association with integrated read-out electronics. The advantages of direct conversion for X-ray and {gamma}-ray detectors and the choice of CdTe is presented first. Then some applications of the CdTe detector are presented: high-energy X-ray tomograph for the control of radioactive waste drums, high definition X-ray imager for medical applications, high-energy X-ray imager for military simulation programs, {gamma}-ray imager for astrophysics applications, and a medical gamma camera to replace the standard Anger camera used in nuclear medicine. (J.S.)

  2. 640 X 480 Pace HgCdTe FPA

    Science.gov (United States)

    Kozlowski, Lester J.; Bailey, Robert B.; Cabelli, Scott A.; Cooper, Donald E.; McComas, Gail D.; Vural, Kadri; Tennant, William E.

    1992-12-01

    A hybrid HgCdTe 640 X 480 infrared (IR) focal plane array (FPA) that meets the sensitivity, resolution, and field-of-view requirements of high-performance medium wavelength infrared (MWIR) imaging systems has been developed. The key technology making this large, high sensitivity device producible is the epitaxial growth of HgCdTe on a CdTe-buffered, sapphire substrate (referred to as PACE, for Producible Alternative to CdTe for Epitaxy; PACE-I refers to sapphire). The device offers TV resolution with excellent sensitivity at temperatures below 120 K. Mean NE(Delta) T as low as 13 mK has been achieved at operating temperatures nonuniformity compensation.

  3. Modeling Copper Diffusion in Polycrystalline CdTe Solar Cells

    Energy Technology Data Exchange (ETDEWEB)

    Akis, Richard [Arizona State University; Brinkman, Daniel [Arizona State University; Sankin, Igor [First Solar; Fang, Tian [First Solar; Guo, Da [Arizona State Univeristy; Vasileska, Dragica [Arizona State University; Ringhofer, Christain [Arizona State University

    2014-06-06

    It is well known that Cu plays an important role in CdTe solar cell performance as a dopant. In this work, a finite-difference method is developed and used to simulate Cu diffusion in CdTe solar cells. In the simulations, which are done on a two-dimensional (2D) domain, the CdTe is assumed to be polycrystalline, with the individual grains separated by grain boundaries. When used to fit experimental Cu concentration data, bulk and grain boundary diffusion coefficients and activation energies for CdTe can be extracted. In the past, diffusion coefficients have been typically obtained by fitting data to simple functional forms of limited validity. By doing full simulations, the simplifying assumptions used in those analytical models are avoided and diffusion parameters can thus be determined more accurately

  4. Extracting Cu Diffusion Parameters in Polycrystalline CdTe

    Energy Technology Data Exchange (ETDEWEB)

    Akis, Richard [Arizona State Univeristy; Brinkman, Daniel [Arizona State Univeristy; Sankin, Igor [First Solar; Fang, Tian [First Solar; Guo, Da [Arizona State Univeristy; Dragica, Vasileska [Arizona State Univeristy; Ringhofer, Christian [Arizona State University

    2014-06-13

    It is well known that Cu plays an important role in CdTe solar cell performance as a dopant. In this work, a finite-difference method is developed and used to simulate Cu diffusion in CdTe solar cells. In the simulations, which are done on a two-dimensional (2D) domain, the CdTe is assumed to be polycrystal-line, with the individual grains separated by grain boundaries. When used to fit experimental Cu concentration data, bulk and grain boundary diffusion coefficients and activation energies for CdTe can be extracted. In the past, diffusion coefficients have been typically obtained by fitting data to simple functional forms of limited validity. By doing full simulations, the simplifying assumptions used in those analytical models are avoided and diffusion parameters can thus be determined more accurately.

  5. Spatial Distribution of Dopant Incorporation in CdTe

    Energy Technology Data Exchange (ETDEWEB)

    Guthrey, Harvey; Moseley, John; Colegrove, Eric; Burst, James; Albin, David; Metzger, Wyatt; Al-Jassim, Mowafak

    2016-11-21

    In this work we use state-of-the-art cathodoluminescence (CL) spectrum imaging that provides spectrum-per-pixel mapping of the CL emission to examine how dopant elements are incorporated into CdTe. Emission spectra and intensity are used to monitor the spatial distribution of additional charge carriers through characteristic variations in the CL emission based on theoretical modeling. Our results show that grain boundaries play a role in the incorporation of dopants in CdTe, whether intrinsic or extrinsic. This type of analysis is crucial for providing feedback to design different processing schedules that optimize dopant incorporation in CdTe photovoltaic material, which has struggled to reach high carrier concentration values. Here, we present results on CdTe films exposed to copper, phosphorus, and intrinsic doping treatments.

  6. Analysis of Etched CdZnTe Substrates

    Science.gov (United States)

    Benson, J. D.; Bubulac, L. O.; Jaime-Vasquez, M.; Lennon, C. M.; Arias, J. M.; Smith, P. J.; Jacobs, R. N.; Markunas, J. K.; Almeida, L. A.; Stoltz, A.; Wijewarnasuriya, P. S.; Peterson, J.; Reddy, M.; Jones, K.; Johnson, S. M.; Lofgreen, D. D.

    2016-09-01

    State-of-the-art as-received (112)B CdZnTe substrates have been examined for surface impurity contamination and polishing residue. Two 4 cm × 4 cm and one 6 cm × 6 cm (112)B state-of-the-art as-received CdZnTe wafers were analyzed. A maximum surface impurity concentration of Al = 1.7 × 1015 atoms cm-2, Si = 3.7 × 1013 atoms cm-2, Cl = 3.12 × 1015 atoms cm-2, S = 1.7 × 1014 atoms cm-2, P = 1.1 × 1014 atoms cm-2, Fe = 1.0 × 1013 atoms cm-2, Br = 1.2 × 1014 atoms cm-2, and Cu = 4 × 1012 atoms cm-2 was observed on the as-received CdZnTe wafers. CdZnTe particulates and residual SiO2 polishing grit were observed on the surface of the as-received (112)B CdZnTe substrates. The polishing grit/CdZnTe particulate density on CdZnTe wafers was observed to vary across a 6 cm × 6 cm wafer from ˜4 × 107 cm-2 to 2.5 × 108 cm-2. The surface impurity and damage layer of the (112)B CdZnTe wafers dictate that a molecular beam epitaxy (MBE) preparation etch is required. The contamination for one 4 cm × 4 cm and one 6 cm × 6 cm CdZnTe wafer after a standard MBE Br:methanol preparation etch procedure was also analyzed. A maximum surface impurity concentration of Al = 2.4 × 1015 atoms cm-2, Si = 4.0 × 1013 atoms cm-2, Cl = 7.5 × 1013 atoms cm-2, S = 4.4 × 1013 atoms cm-2, P = 9.8 × 1013 atoms cm-2, Fe = 1.0 × 1013 atoms cm-2, Br = 2.9 × 1014 atoms cm-2, and Cu = 5.2 × 1012 atoms cm-2 was observed on the MBE preparation-etched CdZnTe wafers. The MBE preparation-etched surface contamination consists of Cd(Zn)Te particles/flakes. No residual SiO2 polishing grit was observed on the (112)B surface.

  7. Au/Cu2Te/CdTe/CdS/TCO/Glass Solar Cells with CdIn2O4 Obtained by Sol-Gel as TCO

    OpenAIRE

    J. Márquez Marín; G. Torres Delgado; M. A. Aguilar Frutis; R. Castanedo Pérez; Zelaya Ángel, O.

    2014-01-01

    An Au/Cu2Te/CdTe/CdS/TCO/glass heterostructure based superstrate solar cells with 2.5 mm2 of area, where the CdTe layer was prepared by means of closed spaced sublimation (CSS) and the CdS by chemical bath, reached an efficiency η value of 12.1%. As transparent conductive oxide (TCO), a thin film of cadmium-indium oxide (CdIn2O4:CIO), obtained by sol-gel technique, was used. A systematic optimization of the thermal activation of the CdTe/CdS/CIO central part of the device with a CdCl2 vapor a...

  8. Phase diagram of Er-Sn-Te system for diluted magnetic semiconductor developments

    Institute of Scientific and Technical Information of China (English)

    张广华; 湛永钟; 李春流

    2013-01-01

    Phase diagrams of the RE (rare earth)-IV-VI systems are very important for the design of rare earth doped diluted magnetic semiconductors (DMSs), but related information is very limited. In this work, the phase equilibria of the Er-Sn-Te system in whole compositional range at room temperature were investigated mainly by means of X-ray powder diffraction (XRD) and differential thermal analysis (DTA). The existences of 9 binary compounds, i.e., SnTe, ErTe3, Er2Te3, ErTe, Er5Sn3, Er11Sn10, ErSn2, Er3Sn7 and Er2Sn5 were confirmed. The phase diagram consisted of 12 single-phase regions, 21 binary phase regions and 10 ternary phase re-gions. The maximum solid solubility of Er in SnTe was determined to be about 7.5 at.%, none of the other phases in this system re-vealed a remarkable homogeneity range at room temperature. No ternary compound was found in this work.

  9. Effect of CdTe Deposition Conditions by Close Spaced Sublimation on Photovoltaic Properties of CdS/CdTe Solar Cells

    Energy Technology Data Exchange (ETDEWEB)

    Han, B.W.; Ahn, J.H.; Ahn, B.T. [Korea Advanced Institute of Science and Technology, Taejon (Korea, Republic of)

    1998-06-01

    CdTe films were deposited by close spaced sublimation with various substrate temperatures, cell areas, and thickness of CdTe and ITO layers and their effects on the CdS/CdTe solar cells were investigated. The resistivity of CdTe layers employed in this study was 3 X 10{sup 4} {Omega}.cm. For constant substrate temperature the optimum substrate temperature for CdTe deposition was 600 deg. C. To obtain larger grain size and more compact microstructure, CdTe film was initially deposited at 620 deg. C, and then deposited at 540 deg. C. The CdTe film was annealed at 620 deg. C and 600 deg. C sequentially to maintain the CdTe film quality. The photovoltaic cell efficiency improved by the two-wave process. For constant substrate temperature, the optimum thickness for CdTe was 5-6{mu}m. Above 6{mu}m CdTe thickness, the bulk resistance of CdTe film degraded the cell performance. As the cell area increased the V{sub oc} remained almost constant, while J{sub sc} and FF strongly decreased because of the increase of lateral resistance of the ITO layer. The optimum thickness of the ITO layer in this study was 300-450nm. In this experiment we obtained the efficiency of 9.4% in the 0.5cm{sup 2} cells. The series resistance of the cell should be further reduced to increase the fill factor and improve the efficiency. (author). 9 refs.,10 figs.

  10. CdTe Photovoltaic Devices for Solar Cell Applications

    Science.gov (United States)

    2011-12-01

    July 28, 2011 14. ABSTRACT Cadmium telluride ( CdTe ) has been recognized as a promising photovoltaic material for thin - film solar cells because of...mail.mil Phone: 301 394 0963 ABSTRACT Cadmium telluride ( CdTe ) has been recognized as a promising photovoltaic material for thin - film ...absorption coefficient allows films as thin as 2 μm to absorb more than 98% of the above-bandgap radiation. Cells with efficiencies near 17% have been

  11. Dynamic effects in CdTe quantum-dot LEDs

    OpenAIRE

    Gallardo, D. E.

    2006-01-01

    In this work the electrical and electroluminescence properties CdTe nanocrystal films were analysed. The structure consisted of a multilayer of CdTe nanocrystals deposited by the layer-by-layer technique, sandwiched between an ITO anode and an aluminium cathode. The first part of this work was dedicated to structural and process improvement. Earlier devices, produced through a layer-by-layer (LbL) manual procedure, had an average thickness of 30nm per nanocrystal monolayer,...

  12. Leakage current measurements on pixelated CdZnTe detectors

    NARCIS (Netherlands)

    Dirks, B.P.F.; Blondel, C.; Daly, F.; Gevin, O.; Limousin, O.; Lugiez, F.

    2006-01-01

    In the field of the R&D of a new generation hard X-ray cameras for space applications we focus on the use of pixelated CdTe or CdZnTe semiconductor detectors. They are covered with 64 (0.9×0.9 mm2) or 256 (0.5×0.5 mm2) pixels, surrounded by a guard ring and operate in the energy ranging from several

  13. Correlation of Interfacial Transportation Properties of CdS/CdTe Heterojunction and Performance of CdTe Polycrystalline Thin-Film Solar Cells

    OpenAIRE

    Guanggen Zeng; Jingquan Zhang; Wenwu Wang; Lianghuan Feng

    2015-01-01

    The light and dark output performances of CdS/CdTe solar cells made by close-spaced sublimation (CSS) were investigated to elucidate the transportation properties of carriers at CdS/CdTe heterojunction interface. It has been found that the interfacial transportation properties were relatively sensitive to variations of the characteristics of heterojunction due to the series resistance and shunting effects. For the high quality cell with 12.1% efficiency, narrow depletion region of ~1.1 micron...

  14. High-quality CdTe films from nanoparticle precursors

    Energy Technology Data Exchange (ETDEWEB)

    Schulz, D.L.; Pehnt, M.; Urgiles, E. [National Renewable Energy Lab., Golden, CO (United States)] [and others

    1996-05-01

    In this paper the authors demonstrate that nanoparticulate precursors coupled with spray deposition offers an attractive route into electronic materials with improved smoothness, density, and lower processing temperatures. Employing a metathesis approach, cadmium iodide was reacted with sodium telluride in methanol solvent, resulting in the formation of soluble NaI and insoluble CdTe nanoparticles. After appropriate chemical workup, methanol-capped CdTe colloids were isolated. CdTe thin film formation was achieved by spray depositing the nanoparticle colloids (25-75 {Angstrom} diameter) onto substrates at elevated temperatures (T = 280-440{degrees}C) with no further thermal treatment. These films were characterized by x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). Cubic CdTe phase formation was observed by XRD, with a contaminant oxide phase also detected. XPS analysis showed that CdTe films produced by this one-step method contained no Na or C and substantial O. AFM gave CdTe grain sizes of {approx}0.1-0.3 {mu}m for film sprayed at 400{degrees}C. A layer-by-layer film growth mechanism proposed for the one-step spray deposition of nanoparticle precursors will be discussed.

  15. Solvothermal preparation and thermoelectric properties of quasi-binary Sn(Pb)Te-Bi2Te3 compounds

    Institute of Scientific and Technical Information of China (English)

    周西松; 邓元; 韦国丹; 刘静; 南策文

    2003-01-01

    Bulk samples of quasi-binary compounds in the Sn(Pb)Te-Bi2Te3 system were prepared by solvothermal method followed by a sintering procedure of compacted pellets. The formation mechanism of the precursor powders, microstructure and thermoelectric properties of the final bulk samples were studied.

  16. Recent advances in thin film CdTe solar cells

    Science.gov (United States)

    Ferekides, Chris S.; Ceekala, Vijaya; Dugan, Kathleen; Killian, Lawrence; Oman, Daniel; Swaminathan, Rajesh; Morel, Don

    1996-01-01

    CdTe thin film solar cells have been fabricated on a variety of glass substrates (borosilicate and soda lime). The CdS films were deposited to a thickness of 500-2000 Å by the chemical bath deposition (CBD), rf sputtering, or close spaced sublimation (CSS) processes. The CdTe films were deposited by CSS in the temperature range of 450-625 °C. The main objective of this work is to fabricate high efficiency solar cells using processes that can meet low cost manufacturing requirements. In an attempt to enhance the blue response of the CdTe cells, ZnS films have also been prepared (CBD, rf sputtering, CSS) as an alternative window layer to CdS. Device behavior has been found to be consistent with a recombination model.

  17. Growth and characterization of CdTe and CdZnTe crystals for substrate application

    Science.gov (United States)

    Azoulay, Moshe; Zilber, Raphael; Shusterman, Sergy; Goldgirsh, Alex; Zontag, Itzhak

    2003-01-01

    During the last decade we have investigated the synthesis, growth and characterization of CdTe and CdZnTe semiconductor compounds. As a result, substrate crystals, suitable for mercury cadmium telluride thin film growth are prepared. The emphasis will be given to the investigation of the thermal regime during growth, reflected at the solid liquid interface shape and its influence on the crystalline quality. Seeded and unseeded growth experiments are compared in terms of structural crystalline quality. Seeded and unseeded growth experiments are compared in terms of structural crystalline perfection as well as single crystal yield. The effect of thermal annealing on IR transmittance, precipitates and inclusions will be discussed in detail. Moreover, we will show the recent new trends for simulation of crystal growth processes by CRYSVUN software as well as practical implementation of calculated data for the grwoth of II-VI crystals. Preliminary study on the vapor phase control during growth and crystal cooling procedures will also be discussed.

  18. CdS/CdTe solar cells with MoOx as back contact buffers

    Science.gov (United States)

    Lin, Hao; Xia, Wei; Wu, Hsiang N.; Tang, Ching W.

    2010-09-01

    Ohmic back contacts for CdS/CdTe solar cells with MoOx as the contact buffer have been demonstrated. With contacts such as MoOx/Ni and MoOx/Al, cell efficiencies comparable to those with conventional back contacts have been produced. Thermal stress tests indicate that MoOx is effective in suppressing metal diffusion into p-CdTe. The usefulness of MoOx is attributed to its unusually high work function which is needed to match that of p-type CdTe in producing contacts of low resistance.

  19. Can we improve the record efficiency of CdS/CdTe solar cells?

    Energy Technology Data Exchange (ETDEWEB)

    Morales-Acevedo, Arturo [CINVESTAV del IPN, Electrical Engineering Department, Avenida IPN No. 2508, 07360 Mexico, D.F. (Mexico)

    2006-09-22

    Polycrystalline thin film CdTe continues to be a leading material for the development of cost effective and reliable photovoltaic systems. The two key properties of this material are its near ideal band gap for photovoltaic conversion efficiency of 1.45eV, and its high optical absorption coefficient. Thin film CdTe solar cells are typically hetero-junctions with CdS being the n-type partner, or window layer. Efficiencies as high as 16.5% have been achieved. In this paper we make a physical analysis of the typical CdS/CdTe superstrate solar cell, and we show that present record efficiencies are very close to the practical efficiency limit for a CdS/CdTe hetero-junction cell. We show that a current estimate for the maximum efficiency of hetero-junction CdS/CdTe solar cells is around 17.5%, in contrast to old theoretical predictions, which calculate about 30% efficiencies for ideal homo-junction CdTe solar cells. This analysis explains why the record efficiency for this kind of cells has been stable for the last 10 years, going up by less than 1% from 15.8% to only 16.5%. (author)

  20. Cross-Sectional Study of Macrodefects in MBE Dual-Band HgCdTe on CdZnTe

    Science.gov (United States)

    Reddy, M.; Lofgreen, D. D.; Jones, K. A.; Peterson, J. M.; Radford, W. A.; Benson, J. D.; Johnson, S. M.

    2013-11-01

    HgCdTe dual-band mid-wave infrared/long-wave infrared focal-plane arrays on CdZnTe are a key component in advanced electrooptic sensor applications. Molecular beam epitaxy (MBE) has been used successfully for growth of dual-band layers on larger CdZnTe substrates. However, the macrodefect density, which is known to reduce the pixel operability and its run-to-run variation, is larger when compared with layers grown on Si substrate. This paper reports the macrodefect density versus size signature of a well-optimized MBE dual-band growth and a cross-sectional study of a macrodefect that represents the most prevalent class using focused ion beam, scanning transmission electron microscopy, and energy-dispersive x-ray spectroscopy. The results show that the macrodefect originates from a void, which in turn is associated with a pit on the CdZnTe substrate.

  1. TEM characterization of MBE grown CdTe/ZnTe axial nanowires.

    Science.gov (United States)

    Dłuzewski, P; Janik, E; Kret, S; Zaleszczyk, W; Tang, D; Karczewski, G; Wojtowicz, T

    2010-03-01

    CdTe/ZnTe axial nanowires were successfully fabricated by molecular beam epitaxy with the use of Au nano-catalysts and vapour-liquid-solid growth mechanism. Nanowires had zinc-blende structure with numerous stacking faults in the bottom ZnTe part and near perfect crystalline structure in the top CdTe part. Energy dispersive X-ray spectroscopy (EDXS) and lattice fringe spacing analysis revealed nonabrupt nature of hetero-interface, whose width was estimated to be 50-70 nm for the nanowires having a diameter in the range from 40 to 50 nm.

  2. The large-area CdTe thin film for CdS/CdTe solar cell prepared by physical vapor deposition in medium pressure

    Science.gov (United States)

    Luo, Run; Liu, Bo; Yang, Xiaoyan; Bao, Zheng; Li, Bing; Zhang, Jingquan; Li, Wei; Wu, Lili; Feng, Lianghuan

    2016-01-01

    The Cadmium telluride (CdTe) thin film has been prepared by physical vapor deposition (PVD), the Ar + O2 pressure is about 0.9 kPa. This method is a newer technique to deposit CdTe thin film in large area, and the size of the film is 30 × 40 cm2. This method is much different from the close-spaced sublimation (CSS), as the relevance between the source temperature and the substrate temperature is weak, and the gas phase of CdTe is transferred to the substrate by Ar + O2 flow. Through this method, the compact and uniform CdTe film (30 × 40 cm2) has been achieved, and the performances of the CdTe thin film have been determined by transmission spectrum, SEM and XRD. The film is observed to be compact with a good crystallinity, the CdTe is polycrystalline with a cubic structure and a strongly preferred (1 1 1) orientation. Using the CdTe thin film (3 × 5 cm2) which is taken from the deposited large-area film, the 14.6% efficiency CdS/CdTe thin film solar cell has been prepared successfully. The structure of the cell is glass/FTO/CdS/CdTe/graphite slurry/Au, short circuit current density (Jsc) of the cell is 26.9 mA/cm2, open circuit voltage (Voc) is 823 mV, and filling factor (FF) is 66.05%. This technique can be a quite promising method to apply in the industrial production, as it has great prospects in the fabricating of large-area CdTe film.

  3. CdTe/ZnTe Quantum Dots - Growth and Optical Properties

    Science.gov (United States)

    2002-06-03

    either of the QD Parameters of the samples studied in this paper: substrate temperature, time of healing, nominal CdTe thickness and the number of... CdTe thickness of 2 ML one can easily distinguish both in Fig. la. QW- and QD-related emissions, while for the sample Both these effects are most...probably responsible for with the nominal CdTe thickness of 4 ML the QW the observed broadening of the PL line in the investi- emission is no longer

  4. Influence of the optical window on the performance of TCO/CdS/CdTe solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Gordillo, G. [Universidad Nacional de Colombia, Bogota (Colombia). Dept. de Fisica; Grizalez, M. [Univ. de la Amazonia, Florencia (Colombia); Moreno, L.C. [Dept. de Quimica, Univ. Nacional de Colombia, Bogota (Colombia); Landazabal, F. [Dept. de Fisica, Univ. de Cundinamarca, Fusagasuga (Colombia)

    2000-07-01

    Thin film solar cells, with structure TCO/CdS/CdTe/Cu, were fabricated using the transparent conducting oxides (TCOs) SnO{sub 2}:F, deposited by spray pyrolysis, and ZnO, deposited by reactive evaporation, as transparent electrodes. The TCO/CdS system with the CdS layer deposited by CBD (chemical bath deposition) method acts in the cell as an optical window and the CdTe deposited by CSS (close space sublimation) method acts as absorber layer, being the unique active layer of the cell. Details of the technological aspects of the solar cells fabrication as well as a discussion to explain the effect of the TCO layer on the solar cell performance will be given. The best results obtained in this work were: open circuit voltage of 0.57 V, short circuit current of 13 mA/cm{sup 2}, fill factor of 0.63 and conversion efficiency of 5.8%. (orig.)

  5. RF Sputtered ZnTe:N as CdS/CdTe Solar Cell Back-Contact Material

    Science.gov (United States)

    Ma, X.

    1999-04-01

    The most frequently used electrical contact to CdTe thin-film polycrystalline solar cells on glass involves the use of copper. However, Cu is known to be a fast diffuser in many semiconductors and is suspected of leading to some deterioration of performance of CdTe solar cells under extreme conditions. In this work we report on the development of a reactively sputtered ZnTe:N back contact on solar cells. Promising low-resistive nitrogen-doped ZnTe films were obtained. Efficiencies up to 10.8 percent were obtained for solar cells fabricated with a ZnTe:N/Au back contact scheme. Comparison of cell performances using ZnTe:N and Cu/Au back-contacts is presented.

  6. Fabrication of CdTe/NiTe films on Ni foils by radio-frequency magnetron sputtering method

    Energy Technology Data Exchange (ETDEWEB)

    Mu, Yannan [National Key Lab of Superhard Materials, Jilin University, Changchun 130012 (China); Department of Physics and Chemistry, Heihe University, Heihe 164300 (China); Zhou, Xiaoming [College of Physics, Beihua University, Jilin 132013 (China); Yao, Huizhen; Su, Shi; Lv, Pin; Chen, Yanli; Wang, Jun; Fu, Wuyou [National Key Lab of Superhard Materials, Jilin University, Changchun 130012 (China); Song, Wenxu [College of Electrical and Information Engineering, Beihua University, Jilin 132013 (China); Yang, Haibin, E-mail: yanghb@jlu.edu.cn [National Key Lab of Superhard Materials, Jilin University, Changchun 130012 (China)

    2015-04-25

    Highlights: • The effects of T{sub s} on CdTe deposited on Ni by magnetron sputtering is investigated. • An effective method is studied of making CdTe/NiTe without post-treatment. • As-prepared CdTe/NiTe raised optical absorption and PEC properties. • Pre-deposited Te can react with Ni to generate NiTe at T{sub s} = 350 °C. - Abstract: Cadmium Telluride (CdTe) semiconductor thin films are fabricated on flexible Ni foil substrates using radio-frequency (RF) magnetron sputtering under different substrate temperatures. The crystal structure and properties of the prepared functional thin films were characterized with series analysis technologies. The characterization results revealed that Nickel Telluride (NiTe) phase formatted at the interface of CdTe and Ni substrate when substrate temperature (T{sub s}) is 450 °C. Specially, XRD results demonstrated that CdTe/NiTe films could also be obtained by pre-depositing Te film on Ni and reducing T{sub s} to 350 °C. The investigation on optical and photoelectrochemical (PEC) properties of the products illustrated that compact CdTe/NiTe films had improved the absorption in the visible region. Furthermore, PEC measurements indicated that CdTe/NiTe/Ni photoelectrode can have a promising application in photovoltaic devices.

  7. Facile synthesis of straight and branched CdTe nanowires using CdO as precursor.

    Science.gov (United States)

    Liu, Sheng; Yang, Chunyan; Zhang, Wen-Hua; Li, Can

    2011-12-01

    High-quality colloidal CdTe nanowires (NWs) containing both straight and branched ones were controllably prepared via a solution-based approach, using a low melting Bi nanoparticles as catalysts, CdO and tributylphosphine telluride (TBP-Te) as precursors, and a tri-n-octylphosphine oxide/tri-n-octylphosphine (TOPO/TOP) mixture as solvent. The resulting straight CdTe NWs have typical diameters below 20 nm accompanying with lengths exceeding 10 microm. In the case of branched CdTe NWs, tripod, V-shaped and y-shaped morphologies are obtained by decreasing the apparent Cd/Te molar ratio. It is found that, as the surface capping ligands, di-n-octylphosphinic acid (DOPA) is superior to decylphosphonic acid (DPA) in the reproducible growth of high-quality CdTe NWs. Since highly toxic dimethylcadmium, a cadmium precursor widely used in literatures, is replaced by CdO and the amount of the TOPO/TOP solvent mixture is significantly reduced, a relative safe and economical synthetic approach of high-quality colloidal CdTe NWs with controllable morphology is thus presented.

  8. Impact of CdS annealing atmosphere on the performance of CdS–CdTe solar cell

    Energy Technology Data Exchange (ETDEWEB)

    Maticiuc, N., E-mail: nataliamaticiuc@yahoo.com; Spalatu, N.; Mikli, V.; Hiie, J.

    2015-09-30

    Highlights: • Annealed CdS films are used for CdTe based solar cells. • CdS–CdTe solar cell with air annealed CdS shows better performance. • The air annealed CdS brings the O{sub 2} and chloride at the place of junction formation. • H{sub 2} removes the oxygen containing compounds from CdS grain boundaries. - Abstract: CdS thin films obtained by chemical bath deposition and annealed in hydrogen and air ambients were combined with CdTe absorbers obtained by close spaced sublimation. CdS–CdTe solar cells in superstrate configuration were characterized by current–voltage and quantum efficiency measurements while the analysis of annealed CdS films was made by scanning electron microscopy, X-ray diffraction and UV–vis spectroscopy. It was found that in superstrate configuration, due to the big grains on CdS surface and gas emission from CdS film at high temperature deposition of the absorber, the delamination of layers take place. Annealing in H{sub 2} removes the oxygen compounds from CdS grain boundaries and opens them for formation of shortcutting through the CdS layer. The processing in air is most advantageous due to simultaneous presence of chloride and oxygen, contributing to the recrystallization and sintering of the highly textured columnar CdS. The direct influence of the CdS annealing on the solar cell parameters is shown for CdS–CdTe solar cell.

  9. Thermal stability of substitutional ag in CdTe

    NARCIS (Netherlands)

    Jahn, SG; Hofsass, H; Restle, M; Ronning, C; Quintel, H; BharuthRam, K; Wahl, U

    1996-01-01

    The thermal stability of substitutional Ag in CdTe was deduced from lattice location measurements at different temperatures. Substitutional Ag probe atoms were generated via transmutation doping from radioactive Cd isotopes. The lattice sites of Ag isotopes were determined by measuring the channelin

  10. Electrostatic assembles and optical properties of Au CdTe QDs and Ag/Au CdTe QDs

    Science.gov (United States)

    Yang, Dongzhi; Wang, Wenxing; Chen, Qifan; Huang, Yuping; Xu, Shukun

    2008-09-01

    Au-CdTe and Ag/Au-CdTe assembles were firstly investigated through the static interaction between positively charged cysteamine-stabilized CdTe quantum dots (QDs) and negatively charged Au or core/shell Ag/Au nano-particles (NCs). The CdTe QDs synthesized in aqueous solution were capped with cysteamine which endowed them positive charges on the surface. Both Au and Ag/Au NCs were prepared through reducing precursors with gallic acid obtained from the hydrolysis of natural plant poly-phenols and favored negative charges on the surface of NCs. The fluorescence spectra of CdTe QDs exhibited strong quenching with the increase of added Au or Ag/Au NCs. Railey resonance scattering spectra of Au or Ag/Au NCs increased firstly and decreased latter with the concentration of CdTe QDs, accompanied with the solution color changing from red to purple and colorless at last. Experimental results on the effects of gallic acid, chloroauric acid tetrahydrate and other reagents demonstrated the static interaction occurred between QDs and NCs. This finding reveals the possibilities to design and control optical process and electromagnetic coupling in hybrid structures.

  11. Nanoscale morphology of multilayer PbTe/CdTe heterostructures and its effect on photoluminescence properties.

    Science.gov (United States)

    Karczewski, G; Szot, M; Kret, S; Kowalczyk, L; Chusnutdinow, S; Wojtowicz, T; Schreyeck, S; Brunner, K; Schumacher, C; Molenkamp, L W

    2015-03-27

    We study nanoscale morphology of PbTe/CdTe multilayer heterostuctures grown by molecular beam epitaxy on hybrid GaAs/CdTe (100) substrates. Nominally, the structures consist of 25 repetitions of subsequently deposited CdTe and PbTe layers with comparable thicknesses of 21 and 8 nm, respectively. However, the morphology of the resulting structures crucially depends on the growth temperature. The two-dimensional layered, superlattice-like character of the structures remains preserved only when grown at low substrate temperatures, such as 230 °C. The samples grown at the slightly elevated temperature of 270 °C undergo a morphological transformation to structures consisting of CdTe and PbTe pillars and columns oriented perpendicular to the substrate. Although the pillar-like objects are of various shapes and dimensions these structures exhibit exceptionally strong photoluminescence in the near infrared spectral region. At the higher growth temperature of 310 °C, PbTe and CdTe separate completely forming thick layers oriented longitudinally to the substrate plane. The observed topological transformations are driven by thermally activated atomic diffusion in the solid state phase. The solid state phase remains fully coherent during the processes. The observed topological transitions leading to the material separation in PbTe/CdTe system could be regarded as an analog of spinodal decomposition of an immiscible solid state solution and thus they can be qualitatively described by the Cahn-Hillard model as proposed by Groiss et al (2014 APL Mater. 2 012105).

  12. Investigation of electroluminescence properties of CdTe@CdS core-shell nanocrystals (NCs)

    Indian Academy of Sciences (India)

    M Molaei; S Pourjafari

    2014-02-01

    In this work, CdTe@CdS NCs were synthesized using a thermochemical approach and synthesized NCs were used as an emissive layer, a light emitting device, with ITO/MoO3/PVK/CdTe@CdS(core-shell)/Mg:Ag structure. Structural and optical properties of synthesized NCs were investigated by means of XRD, UV–Vis and photoluminescence (PL) analyses. Fabricated device was characterized by electroluminescence spectra. XRD analysis demonstrated cubic phase NCs. Photoluminescence spectra showed a narrow band emission with a peak centred at about 600 nm. Fabricated device showed an emission at 600 nm, which is related to CdTe@CdS NCs. Turn on voltage of fabricated device is about 8 V and brightness is 53.7 Cd/m2 at a working voltage of about 14.57 V.

  13. CdS: Characterization and recent advances in CdTe solar cell performance

    Energy Technology Data Exchange (ETDEWEB)

    Ferekides, C.; Marinskiy, D.; Morel, D.L. [Univ. of South Florida, FL (United States)

    1997-12-31

    Cadmium sulfide (CdS) films deposited by chemical bath deposition (CBD) have been used for the fabrication of high efficiency CdTe and CuIn{sub 1{minus}x}Ga{sub x}Se{sub 2} thin film solar cells. An attractive alternative deposition technology with manufacturing advantages over the CBD is the close spaced sublimation (CSS). In this work CdTe/CdS solar cells prepared entirely by the CSS process exhibited 15.0% efficiencies under global AM1.5 conditions as verified at the National Renewable Energy Laboratory. This paper reports on studies carried out on as deposited and heat treated CSS CdS films and all CSS CdTe/CdS solar cells using photoluminescence, x-ray diffraction, and I-V-T measurements.

  14. Stoichiometry dependence of resistance drift phenomena in amorphous GeSnTe phase-change alloys

    Science.gov (United States)

    Luckas, J.; Piarristeguy, A.; Bruns, G.; Jost, P.; Grothe, S.; Schmidt, R. M.; Longeaud, C.; Wuttig, M.

    2013-01-01

    In phase-change materials, the amorphous state resistivity increases with time following a power law ρ ∝ (t/t0)αRD. This drift in resistivity seriously hampers the potential of multilevel-storage to achieve an increased capacity in phase-change memories. This paper presents the stoichiometric dependence of drift phenomena in amorphous GeSnTe systems (a-GeSnTe) and other known phase-change alloys with the objective to identify low drift materials. The substitution of Ge by Sn results in a systematic decrease of the drift parameter from a-GeTe (αRD = 0.129) to a-Ge2Sn2Te4 (αRD = 0.053). Furthermore, with increasing Sn content a decrease in crystallization temperature, trap state density, optical band gap, and activation energy for electronic conduction is observed. In a-GeSnTe, a-GeSbTe, and a-AgInSbTe alloys as well, the drift parameter αRD correlates to the activation energy for electronic conduction. This study indicates that low drift materials are characterized by low activation energies of electronic conduction. The correlation found between drift and activation energy of electronic conduction manifests a useful criterion for material optimization.

  15. Band diagrams and performance of CdTe solar cells with a Sb2Te3 back contact buffer layer

    Directory of Open Access Journals (Sweden)

    Songbai Hu

    2011-12-01

    Full Text Available Sb2Te3 thin films were prepared by vacuum co-evaporation and the crystallinity of the films was greatly improved after annealing at 573 K in N2 ambient. Then they were deposited on the CdTe thick films. Band diagrams of the as-deposited and annealed CdTe/Sb2Te3 interfaces were constructed. Consequently, Sb2Te3 was used as a back contact layer for CdTe thin film solar cells and the cell performance was investigated. It was found that the Sb impurities accumulated in the CdTe grain boundaries diffuse deeply in the CdTe layer, and more photogenerated electrons and holes are separated by the segregated SbCd+ donors into the GBs. What is more, the doping concentration in the vicinity of the CdTe/CdS heterojunction increases for the formation of substitutional SbTe- acceptors under the Cd-rich conditions. For the introduction of the p-type Sb2Te3 layers as the back contact to the CdTe thin film solar cells, the performance of CdTe thin film solar cells has been greatly improved and an efficiency of 13.1% (FF=62.3%, Jsc=25.8 mA/cm2, Voc= 815.8 mV obtained.

  16. Effect of Low Concentration Sn Doping on Optical Properties of CdS Films Grown by CBD Technique

    Directory of Open Access Journals (Sweden)

    Mohd Sabri Mohd Ghazali

    2011-09-01

    Full Text Available Thin and transparent films of doped cadmium sulfide (CdS were obtained on commercial glass substrates by Chemical Bath Deposition (CBD technique. The films were doped with low concentration of Sn, and annealed in air at 300 °C for 45 min. The morphological characterization of the films with different amounts of dopant was made using SEM and EDAX analysis. Optical properties of the films were evaluated by measuring transmittance using the UV-vis spectrophotometer. A comparison of the results revealed that lower concentration of Sn doping improves transmittance of CdS films and makes them suitable for application as window layer of CdTe/CIGS solar cells.

  17. Diffusion of Cd and Te adatoms on CdTe(111 surfaces: A computational study using density functional theory

    Directory of Open Access Journals (Sweden)

    Ebadollah Naderi

    2015-01-01

    Full Text Available CdTe is one of the most promising semiconductor for thin-film based solar cells. Here we report a computational study of Cd and Te adatom diffusion on the CdTe (111 A-type (Cd terminated and B-type (Te terminated surfaces and their migration paths. The atomic and electronic structure calculations are performed under the DFT formalism and climbing Nudge Elastic Band (cNEB method has been applied to evaluate the potential barrier of the Te and Cd diffusion. In general the minimum energy site on the surface is labeled as Aa site. In case of Te and Cd on B-type surface, the sub-surface site (a site just below the top surface is very close in energy to the A site. This is responsible for the subsurface accumulation of adatoms and therefore, expected to influence the defect formation during growth. The diffusion process of adatoms is considered from Aa (occupied to Aa (empty site at the nearest distance. We have explored three possible migration paths for the adatom diffusion. The adatom surface interaction is highly dependent on the type of the surface. Typically, Te interaction with both type (5.2 eV for A-type and 3.8 eV for B-type is stronger than Cd interactions(2.4 eV for B-type and 0.39 eV for A-type. Cd interaction with the A-type surface is very weak. The distinct behavior of the A-type and B-type surfaces perceived in our study explain the need of maintaining the A-type surface during growth for smooth and stoichiometric growth.

  18. Diffusion of Cd and Te adatoms on CdTe(111) surfaces: A computational study using density functional theory

    Science.gov (United States)

    Naderi, Ebadollah; Nanavati, Sachin; Majumder, Chiranjib; Ghaisas, S. V.

    2015-01-01

    CdTe is one of the most promising semiconductor for thin-film based solar cells. Here we report a computational study of Cd and Te adatom diffusion on the CdTe (111) A-type (Cd terminated) and B-type (Te terminated) surfaces and their migration paths. The atomic and electronic structure calculations are performed under the DFT formalism and climbing Nudge Elastic Band (cNEB) method has been applied to evaluate the potential barrier of the Te and Cd diffusion. In general the minimum energy site on the surface is labeled as Aa site. In case of Te and Cd on B-type surface, the sub-surface site (a site just below the top surface) is very close in energy to the A site. This is responsible for the subsurface accumulation of adatoms and therefore, expected to influence the defect formation during growth. The diffusion process of adatoms is considered from Aa (occupied) to Aa (empty) site at the nearest distance. We have explored three possible migration paths for the adatom diffusion. The adatom surface interaction is highly dependent on the type of the surface. Typically, Te interaction with both type (5.2 eV for A-type and 3.8 eV for B-type) is stronger than Cd interactions(2.4 eV for B-type and 0.39 eV for A-type). Cd interaction with the A-type surface is very weak. The distinct behavior of the A-type and B-type surfaces perceived in our study explain the need of maintaining the A-type surface during growth for smooth and stoichiometric growth.

  19. Diffusion of Cd and Te adatoms on CdTe(111) surfaces: A computational study using density functional theory

    Energy Technology Data Exchange (ETDEWEB)

    Naderi, Ebadollah, E-mail: enaderi42@gmail.com [Department of Physics, Savitribai Phule Pune University (SPPU), Pune-411007 (India); Nanavati, Sachin [Center for Development of Advanced Computing (C-DAC), SPPU campus, Pune 411007 (India); Majumder, Chiranjib [Chemistry Division, Bhabha Atomic Research Center, Mumbai, 400085 (India); Ghaisas, S. V. [Department of Electronic Science, Savitribai Phule Pune University (SPPU), Pune-411007 (India); Department of Physics, Savitribai Phule Pune University (SPPU), Pune-411007 (India)

    2015-01-15

    CdTe is one of the most promising semiconductor for thin-film based solar cells. Here we report a computational study of Cd and Te adatom diffusion on the CdTe (111) A-type (Cd terminated) and B-type (Te terminated) surfaces and their migration paths. The atomic and electronic structure calculations are performed under the DFT formalism and climbing Nudge Elastic Band (cNEB) method has been applied to evaluate the potential barrier of the Te and Cd diffusion. In general the minimum energy site on the surface is labeled as A{sub a} site. In case of Te and Cd on B-type surface, the sub-surface site (a site just below the top surface) is very close in energy to the A site. This is responsible for the subsurface accumulation of adatoms and therefore, expected to influence the defect formation during growth. The diffusion process of adatoms is considered from A{sub a} (occupied) to A{sub a} (empty) site at the nearest distance. We have explored three possible migration paths for the adatom diffusion. The adatom surface interaction is highly dependent on the type of the surface. Typically, Te interaction with both type (5.2 eV for A-type and 3.8 eV for B-type) is stronger than Cd interactions(2.4 eV for B-type and 0.39 eV for A-type). Cd interaction with the A-type surface is very weak. The distinct behavior of the A-type and B-type surfaces perceived in our study explain the need of maintaining the A-type surface during growth for smooth and stoichiometric growth.

  20. Surface-state-mediated charge-transfer dynamics in CdTe/CdSe core-shell quantum dots.

    Science.gov (United States)

    Rawalekar, Sachin; Kaniyankandy, Sreejith; Verma, Sandeep; Ghosh, Hirendra N

    2011-06-20

    Herein, we report the synthesis of aqueous CdTe/CdSe type-II core-shell quantum dots (QDs) in which 3-mercaptopropionic acid is used as the capping agent. The CdTe QDs and CdTe/CdSe core-shell QDs are characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), steady-state absorption, and emission spectroscopy. A red shift in the steady-state absorption and emission bands is observed with increasing CdSe shell thickness over CdTe QDs. The XRD pattern indicates that the peaks are shifted to higher angles after growth of the CdSe shell on the CdTe QDs. HR-TEM images of both CdTe and CdTe/CdSe QDs indicate that the particles are spherical, with a good shape homogeneity, and that the particle size increases by about 2 nm after shell formation. In the time-resolved emission studies, we observe that the average emission lifetime (τ(av)) increases to 23.5 ns for CdTe/CdSe (for the thickest shell) as compared to CdTe QDs (τ(av) =12 ns). The twofold increment in the average emission lifetime indicates an efficient charge separation in type-II CdTe/CdSe core-shell QDs. Transient absorption studies suggest that both the carrier cooling and the charge-transfer dynamics are affected by the presence of traps in the CdTe QDs and CdTe/CdSe core-shell QDs. Carrier quenching experiments indicate that hole traps strongly affect the carrier cooling dynamics in CdTe/CdSe core-shell QDs.

  1. Morphological control of SnTe nanostructures by tuning catalyst composition

    Institute of Scientific and Technical Information of China (English)

    Yichao Zou[1; Zhigang Chen[1; Jing Lin[1; Xiaohao Zhou[2; Wei Lu[2; John Drennan[3; Jin Zou[1,3

    2015-01-01

    A method of controlling the morphology of SnTe nanostructures produced by a simple chemical vapor deposition is presented, in which Au-containing catalysts with different Au concentrations are used to induce specific growth behavior. Triangular SnTe nanoplates with a {100} dominated surface and {100}, {111} and {120} side facets were induced by AuSn catalysts, whereas 〈010〉 SnTe nanowires with four nonpolar {100} side-facets were produced using AusSn catalysts. Through detailed structural and chemical characterization, coupled with surface energy calculations, it is found that nanowire growth is thermodynamically controlled via a vapor-solid-solid growth mechanism, whereas nanoplate growth is kinetically controlled via a vapor-liquid-solid growth mechanism. Therefore, this study provides a fundamental understanding of the catalyst's role in the growth of IV-VI compound nanostructures.

  2. Thin film CdS/CdTe solar cells fabricated by electrodeposition

    Science.gov (United States)

    Kim, D.; Pozder, S.; Qi, B.; Zhu, Y.; Furtak, T. E.; Williamson, D. L.; Trefny, J. U.

    1994-06-01

    CdTe cells with efficiencies up to 9.58% were fabricated by electrodeposition. The minority-carrier lifetime in the CdTe measured by time-resolved photoluminescence was 2.39 ns. A first method to characterize CdS microstructure by small-angle x-ray scattering method has been made. Scanning tunneling microscopy performed on 1000 Å thick CdS films made by chemical bath deposition revealed a thickness fluctuation of 500 Å. Annealing of the CdS films followed by a CdCl2 treatment did not reduce the roughness, but drastically changed the contour of the grains. Some of the CdCl2-treated CdS showed white spots with diameters ranging from about 0.5 mm to 5 mm. These spots are conglomerates of dendritic patterns of either Cd metal or some Cd-rich phase. Optical transmittance of CdS films with various thicknesses (170 Å-2400 Å) showed a good correlation between thickness and transmittance for photon energies above the bandgap. The effect of CdCl2 treatment and annealing on transmittance was either negligible or slightly deleterious. CdTe films made by electrodeposition showed a dense, faceted surface morphology and films were under compressive stress after CdCl2 treatment and annealing.

  3. High efficiency CSS CdTe solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Ferekides, C.S.; Marinskiy, D.; Viswanathan, V.; Tetali, B.; Palekis, V.; Selvaraj, P.; Morel, D.L. [University of South Florida, Tampa, FL (United States). Dept. of Electrical Engineering

    2000-02-21

    Cadmium telluride (CdTe) has long been recognized as a strong candidate for thin film solar cell applications. It has a bandgap of 1.45 eV, which is nearly ideal for photovoltaic energy conversion. Due to its high optical absorption coefficient essentially all incident radiation with energy above its band-gap is absorbed within 1-2 {mu}m from the surface. Thin film CdTe solar cells are typically heterojunctions, with cadmium sulfide (CdS) being the n-type junction partner. Small area efficiencies have reached the 16.0% level and considerable efforts are underway to commercialize this technology. This paper will present work carried out at the University South Florida sponsored by the National Renewable Energy Laboratory of the United States Department of Energy, on CdTe/CdS solar cells fabricated using the close spaced sublimation (CSS) process. The CSS technology has attractive features for large area applications such as high deposition rates and efficient material utilization. The structural and optical properties of CSS CdTe and CdS films and junctions will be presented and the influence of some important CSS process parameters will be discussed. (orig.)

  4. Thermoelectric properties of Eu-and Na-substituted SnTe

    Institute of Scientific and Technical Information of China (English)

    王新科; 郭凯; Igor Veremchuk4; Ulrich Burkhardt4; 冯贤娟; 赵景泰

    2015-01-01

    Thermoelectric properties of spark-plasma-sintering prepared bulk materials EuxNayzSn1–x–y–zTe above room temperature were investigated. The implementation of Eu and Na into the SnTe lattice was monitored by refinement of lattice parameters as well as energy dispersive X-ray spectroscopy (EDXS). The binary SnTe achieved the highest ZT value of 0.63 at 786 K, and showed a hole concentration of 4.6×1019 cm–3 at 300 K. In comparison with pristine SnTe, the samples containing Eu had lower carrier mobility but higher Hall carrier concentration. For Eu-and Na-substituted samples, the increased hole concentration was unfavorable for the improvement of thermoelectric properties.

  5. Nanosized thin SnO₂ layers doped with Te and TeO₂ as room temperature humidity sensors.

    Science.gov (United States)

    Georgieva, Biliana; Podolesheva, Irena; Spasov, Georgy; Pirov, Jordan

    2014-05-21

    In this paper the humidity sensing properties of layers prepared by a new method for obtaining doped tin oxide are studied. Different techniques-SEM, EDS in SEM, TEM, SAED, AES and electrical measurements-are used for detailed characterization of the thin layers. The as-deposited layers are amorphous with great specific area and low density. They are built up of a fine grained matrix, consisting of Sn- and Te-oxides, and a nanosized dispersed phase of Te, Sn and/or SnTe. The chemical composition of both the matrix and the nanosized particles depends on the ratio R(Sn/Te) and the evaporation conditions. It is shown that as-deposited layers with R(Sn/Te) ranging from 0.4 to 0.9 exhibit excellent characteristics as humidity sensors operating at room temperature-very high sensitivity, good selectivity, fast response and short recovery period. Ageing tests have shown that the layers possess good long-term stability. Results obtained regarding the type of the water adsorption on the layers' surface help better understand the relation between preparation conditions, structure, composition and humidity sensing properties.

  6. Comparative study of CdTe sources used for deposition of CdTe thin films by close spaced sublimation technique

    Directory of Open Access Journals (Sweden)

    Wagner Anacleto Pinheiro

    2006-03-01

    Full Text Available Unlike other thin film deposition techniques, close spaced sublimation (CSS requires a short source-substrate distance. The kind of source used in this technique strongly affects the control of the deposition parameters, especially the deposition rate. When depositing CdTe thin films by CSS, the most common CdTe sources are: single-crystal or polycrystalline wafers, powders, pellets or pieces, a thick CdTe film deposited onto glass or molybdenum substrate (CdTe source-plate and a sintered CdTe powder. In this work, CdTe thin films were deposited by CSS technique from different CdTe sources: particles, powder, compact powder, a paste made of CdTe and propylene glycol and source-plates (CdTe/Mo and CdTe/glass. The largest deposition rate was achieved when a paste made of CdTe and propylene glycol was used as the source. CdTe source-plates led to lower rates, probably due to the poor heat transmission, caused by the introduction of the plate substrate. The results also showed that compacting the powder the deposition rate increases due to the better thermal contact between powder particles.

  7. Identification of Ag-acceptors in $^{111}Ag^{111}Cd$ doped ZnTe and CdTe

    CERN Document Server

    Hamann, J; Deicher, M; Filz, T; Lany, S; Ostheimer, V; Strasser, F; Wolf, H; Wichert, T

    2000-01-01

    Nominally undoped ZnTe and CdTe crystals were implanted with radioactive /sup 111/Ag, which decays to /sup 111/Cd, and investigated by photoluminescence spectroscopy (PL). In ZnTe, the PL lines caused by an acceptor level at 121 meV are observed: the principal bound exciton (PBE) line, the donor-acceptor pair (DAP) band, and the two-hole transition lines. In CdTe, the PBE line and the DAP band that correspond to an acceptor level at 108 meV appear. Since the intensities of all these PL lines decrease in good agreement with the half-life of /sup 111/Ag of 178.8 h, both acceptor levels are concluded to be associated with defects containing a single Ag atom. Therefore, the earlier assignments to substitutional Ag on Zn- and Cd-lattice sites in the respective II-VI semiconductors are confirmed. The assignments in the literature of the S/sub 1/, S /sub 2/, and S/sub 3/ lines in ZnTe and the X/sub 1//sup Ag/, X/sub 2 //sup Ag//C/sub 1//sup Ag/, and C/sub 2//sup Ag/ lines in CdTe to Ag- related defect complexes are ...

  8. (CdTe){sub 1-x}(In{sub 2}Te{sub 3}){sub x} pseudo-binary in polycrystalline CdTe-In films

    Energy Technology Data Exchange (ETDEWEB)

    Castro-Rodriguez, R.; Pena, J.L. [CINVESTAV-IPN, Merida (Mexico). Appl. Phys. Dept.; Hernandez, M.P. [IMRE, University of La Havana, 10400 Vedado, La Habana (Cuba); Zapata-Torres, M. [CICATA-IPN ALTAMIRA, Km. 14.5 Carretera Tampico-Puerto Altamira. Altamira Tamaulipas, C.P. 89600, Altamira (Spain)

    2000-09-03

    Polycrystalline CdTe-In films were prepared using close-spaced vapor transport technique combined with free evaporation (CSVT-FE), and the stoichiometry and structural properties were investigated. Auger electron spectroscopy (AES) was used to quantify the stoichiometry of the indium concentration in the films which increased according to the rise of temperature of the In source. X-ray diffraction analysis allowed to identify the CdTe ({alpha}-phase) in all films, together with the CdIn{sub 2}Te{sub 4} ({beta}-phase) in the films grown at the highest temperatures of the In source. For low In concentration films, the lattice parameter decreased linearly with the molar percent of In{sub 2}Te{sub 3} in CdTe (below 5 mol%). This behavior corroborated the presence of the solid solution. (orig.)

  9. Optical characterization of CdTe/ZnTe semiconductor wires and dots

    OpenAIRE

    Gourgon, C; Eriksson, B; Dang, L.; MARIETTE H.; Vieu, C.

    1993-01-01

    Arrays of wires and dots have been fabricated by electron beam lithography and Ar+ ion beam etching from CdTe/ZnTe quantum wells. Low temperature photoluminescence coming out from these structures is still observed for the smallest wires (40 nm) whereas for the dots, the detection limit occurs for lateral dimensions of 100 nm.

  10. Thermal conductivity studies of CdZnTe with varying Te excess

    Science.gov (United States)

    Jackson, Maxx; Bennett, Brittany; Giltnane, Dustin; Babalola, Stephen; Ohmes, Martin F.; Stowe, A. C.

    2016-09-01

    Cadmium Zine Telluride (CZT) has been extensively studied as a room temperature semiconductor gamma radiation detector. CZT continues to show promise as a bulk and pixelated gamma spectrometer with less than one percent energy resolution; however the fabrication costs are high. Improved yields of high quality, large CZT spectroscopy grade crystals must be achieved. CZT is grown by the Traveling Heater Method (THM) with a Te overpressure to account for vaporization losses. This procedure creates Te rich zones. During growth, boules will often cleave limiting the number of harvestable crystals. As a result, crystal growth parameter optimization was evaluated by modeling the heat flow within the system. Interestingly, Cadmium Telluride (CdTe) is used as a thermal conductivity surrogate in the absence of a thorough study of the CZT thermal properties. The current study has measured the thermal conductivity of CZT pressed powders with varying Te concentrations from 50-100% over 25-800°C to understand the variation in this parameter from CdTe. Cd0.9Zn0.1Te1.0 is the base CZT (designated 50%). CZT exhibits a thermal conductivity of nearly 1 W/mK, an order of magnitude greater than CdTe. Further, the thermal conductivity decreased with increasing Te concentration.

  11. Influence of CdS deposition technique for CdS/CdTe solar cells applications

    Science.gov (United States)

    Rubio, Sandra; Plaza, José Luis; Diéguez, Ernesto

    2014-09-01

    The manufacturing of an optimal window layer is essential for a high efficiency solar cell. CdS thin films were deposited on FTO commercial substrates by two different techniques: Chemical Bath Deposition (CBD), and Closed Space Sublimation (CSS) using SiC rods as electrical heating elements. The composition, morphology, and crystalline structure of the CdS thin films were analyzed by Energy Dispersive X-ray spectroscopy (EDX), Scanning Electron Microscope (SEM), and X-Ray Diffraction (XRD). CdS layers obtained by CSS have shown good stoichiometries of 51.07(Cd at %), and 48.93(S at %), with the presence of disordered microrods of hexagonal shape. The CdS films obtained by CBD exhibited certain contamination from the bath chemical components and a poor defined structure. In conclusion, the layers deposited by electric heating based CSS present a better morphology and crystal structure than the layers deposited by CBD. The CdTe absorber layer deposited by CSS electric heating also shows good cubic structure and morphology.

  12. Au/Cu2Te/CdTe/CdS/TCO/Glass Solar Cells with CdIn2O4 Obtained by Sol-Gel as TCO

    Directory of Open Access Journals (Sweden)

    J. Márquez Marín

    2014-01-01

    Full Text Available An Au/Cu2Te/CdTe/CdS/TCO/glass heterostructure based superstrate solar cells with 2.5 mm2 of area, where the CdTe layer was prepared by means of closed spaced sublimation (CSS and the CdS by chemical bath, reached an efficiency η value of 12.1%. As transparent conductive oxide (TCO, a thin film of cadmium-indium oxide (CdIn2O4:CIO, obtained by sol-gel technique, was used. A systematic optimization of the thermal activation of the CdTe/CdS/CIO central part of the device with a CdCl2 vapor ambient made the conversion efficiency of the Au/Cu2Te/CdTe/CdS/CIO/glass heterostructure reaches 9.94% for the CdTe layer with thickness of 1.8 μm. This efficiency was reached only through an open circuit voltage VOC optimization. A maximum η of 12.1% was reached with the established procedure of optimization and when the CdTe layer thickness was increased to 3.1 ± 0.05 μm. The substitution of CIO by commercial ITO provoked in the cell a decrease of η from 12.1% to 7.2%, both devices prepared under the same conditions. Starting from these results, we can say that CIO was a better TCO than commercial ITO in our solar cell, with the advantage that CIO was obtained by sol-gel, which is a simple and economical technique.

  13. A Comparative Study on the Optical Properties of Multilayer CdSe / CdTe Thin Film with Single Layer CdTe and CdSe Films

    Directory of Open Access Journals (Sweden)

    M. Melvin David Kumar

    2013-07-01

    Full Text Available CdTe and CdSe single layer thin films and CdSe / CdTe multilayer (ML thin film were prepared by using physical vapour deposition method. Optical properties of CdSe / CdTe multilayer thin film shows different behavior due to type II band structure alignment. Energy band gap value of CdSe / CdTe ML thin film is shifted to higher value than that of single layer CdTe film. This is due to decrease in crystallite size to dimension smaller than the Bohr exciton radius of CdTe (14 nm. Crystallite size of the multilayer sample was calculated with the predictions of the effective mass approximation model (i.e., Brus model. It is observed that the photoluminescence peak of CdSe / CdTe ML thin film is red shifted compared to the peaks corresponding to individual CdSe and CdTe thin films. This may be due to the presence of type II quantum dot formation in the CdSe / CdTe heterostructure multilayer thin film.

  14. Recent technical advances in thin-film CdS/CdTe solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Omura, K.; Hanahusa, A.; Arita, T.; Higuchi, H.; Aramoto, T.; Nishio, T.; Sibutani, S.; Kumazawa, S.; Murozono, M. [Matsushita Battery Industrial Co., Ltd., Osaka (Japan). PV Research and Development Center; Yabuuchi, Y. [Matsushita Technoresearch Inc., Osaka (Japan); Takakura, H. [Toyama Prefectural University, Toyama (Japan)

    1996-05-01

    CeS/CdTe solar cells have attracted attention recently for their potential as low-cost, high-efficiency solar cells of the future. It is because the CdTe layer (used for photoelectric conversion) has a bandgap energy of 1.51 eV, which corresponds well to sunlight spectra, and the direct transition type energy band structure enables formation of thinner films. We have already industrialized CdS/CdTe solar cells in mass production stage using a printing-sintering process, as large-area modules for electric power generation (Higuchi et al., 1993, Omura et al., 1991), and as cells for indoor applications (primarily in calculators, Suyama et al., 1986). However, this solar cell has a conversion efficiency of approximately 6%. Recently, there has been considerable research into thin-film CdS/CdTe solar cells which have a thinner CdS film formed by CVD or CBD (Britt et al., 1993) process, and thus are photosensitive to light with wavelengths of 500 nm or less. At present stage of our art, in solar cells formed by the CSS with a CdTe film on CVD CdS, a conversion efficiency of 15.05% has been obtained in cells with an area of 1 cm{sup 2}(verified at JQA). (author)

  15. Analysis of Cu Diffusion in ZnTe-Based Contacts for Thin-Film CdS/CdTe Solar Cells

    Energy Technology Data Exchange (ETDEWEB)

    Narayanswamy, C. (Department of Physics & Astronomy, University of Toledo); Gessert, T. A. and Asher, S. E. (National Renewable Energy Laboratory)

    1998-10-27

    Ohmic contacts to thin-film CdS/CdTe photovoltaic devices have been formed using a two-layer contact interface of undoped ZnTe (ZnTe) and Cu-doped ZnTe (ZnTe:Cu), followed by Ni or Ti as an outer metallization. Secondary ion mass spectroscopy (SIMS) is used to study Cu diffusion within this back-contact structure, and also, to monitor Cu diffusion from the contact into the CdTe. When Ni metallization is used, the ZnTe:Cu layer becomes increasingly depleted of Cu, and Ni diffusion into the ZnTe:Cu increases as the contact deposition temperature increases from 100 C to 300 C. Cu depletion is not observed when Ni is replaced with Ti. Diffusion of Cu from the ZnTe:Cu layer into the ZnTe layer also increases with contact deposition temperature, and produces a buildup of Cu at the ZnTe/CdTe interface. High-mass resolution SIMS indicates that, although Cu levels in the CdTe remain low, Cu diffusion from the contact proceeds into the CdTe layer and toward the CdTe/CdS junction region.

  16. Radio-frequency-magnetron-sputtered CdS/CdTe solar cells on soda-lime glass

    Energy Technology Data Exchange (ETDEWEB)

    Shao, M.; Fischer, A.; Grecu, D.; Jayamaha, U.; Bykov, E.; Contreras-Puente, G.; Bohn, R.G.; Compaan, A.D. [Department of Physics and Astronomy and Center for Materials Science and Engineering, The University of Toledo, Toledo, Ohio 43606 (United States)

    1996-11-01

    We report the fabrication of an 11.6{percent} efficient, polycrystalline thin-film CdS/CdTe solar cell in which both semiconductor layers were deposited by planar-magnetron-radio-frequency sputtering at 380{degree}C on commercially available soda-lime float-glass substrates coated with SnO{sub 2}:F. We show that the magnetron magnetic field is critical to obtaining high cell efficiency. Much stronger photoluminescence and higher electrical conductivity are found in films and cells grown with unbalanced-field magnetrons. The magnetic field dependence is interpreted as arising from the enhanced electron and ion bombardment of the film growth interface when unbalanced magnetrons are used. {copyright} {ital 1996 American Institute of Physics.}

  17. Atmospheric pressure chemical vapor deposition of CdTe for high efficiency thin film PV devices: Annual subcontract report, 26 January 1999--25 January 2000

    Energy Technology Data Exchange (ETDEWEB)

    Meyers, P. V.; Kee, R.; Wolden, C.; Kestner, J.; Raja, L.; Kaydanov, V.; Ohno, T.; Collins, R.; Fahrenbruch, A.

    2000-05-30

    ITN's three year project Atmospheric Pressure Chemical Vapor Deposition (APCVD) of CdTe for High Efficiency Thin Film PV Devices has the overall objectives of improving thin film CdTe PV manufacturing technology and increasing CdTe PV device power conversion efficiency. CdTe deposition by APCVD employs the same reaction chemistry as has been used to deposit 16% efficient CdTe PV films, i.e., close spaced sublimation, but employs forced convection rather than diffusion as a mechanism of mass transport. Tasks of the APCVD program center on demonstration of APCVD of CdTe films, discovery of fundamental mass transport parameters, application of established engineering principles to the deposition of CdTe films, and verification of reactor design principles which could be used to design high throughput, high yield manufacturing equipment. Additional tasks relate to improved device measurement and characterization procedures that can lead to a more fundamental understanding of CdTe PV device operation and ultimately to higher device conversion efficiency and greater stability. Under the APCVD program, device analysis goes beyond conventional one-dimensional device characterization and analysis toward two dimension measurements and modeling. Accomplishments of the second year of the APCVD subcontract include: deposition of the first APCVD CdTe; identification of deficiencies in the first generation APCVD reactor; design, fabrication and testing of a ``simplified'' APCVD reactor; deposition of the first dense, adherent APCVD CdTe films; fabrication of the first APCVD CdTe PV device; modeling effects of CdSTe and SnOx layers; and electrical modeling of grain boundaries.

  18. Fabrication of CdS/CdTe-Based Thin Film Solar Cells Using an Electrochemical Technique

    Directory of Open Access Journals (Sweden)

    I. M. Dharmadasa

    2014-06-01

    Full Text Available Thin film solar cells based on cadmium telluride (CdTe are complex devices which have great potential for achieving high conversion efficiencies. Lack of understanding in materials issues and device physics slows down the rapid progress of these devices. This paper combines relevant results from the literature with new results from a research programme based on electro-plated CdS and CdTe. A wide range of analytical techniques was used to investigate the materials and device structures. It has been experimentally found that n-, i- and p-type CdTe can be grown easily by electroplating. These material layers consist of nano- and micro-rod type or columnar type grains, growing normal to the substrate. Stoichiometric materials exhibit the highest crystallinity and resistivity, and layers grown closer to these conditions show n → p or p → n conversion upon heat treatment. The general trend of CdCl2 treatment is to gradually change the CdTe material’s n-type electrical property towards i-type or p-type conduction. This work also identifies a rapid structural transition of CdTe layer at 385 ± 5 °C and a slow structural transition at higher temperatures when annealed or grown at high temperature. The second transition occurs after 430 °C and requires more work to understand this gradual transition. This work also identifies the existence of two different solar cell configurations for CdS/CdTe which creates a complex situation. Finally, the paper presents the way forward with next generation CdTe-based solar cells utilising low-cost materials in their columnar nature in graded bandgap structures. These devices could absorb UV, visible and IR radiation from the solar spectrum and combine impact ionisation and impurity photovoltaic (PV effect as well as making use of IR photons from the surroundings when fully optimised.

  19. Explanation of red spectral shifts at CdTe grain boundaries

    Science.gov (United States)

    Moseley, John

    The best research-cell efficiencies for CdTe thin-film solar cells have recently increased from 17.3% to 20.4%. Despite these impressive recent gains, many improvements in device technology are necessary to reach the detailed-balance efficiency limit for CdTe-based (single-junction, non-concentrator) solar cells of ~32%. Improvements will increasingly rely on knowledge of the fundamental relationships between processing, electrical properties of defects, and device performance. In this study, scanning electron microscope (SEM)-based cathodoluminescence (CL) spectrum imaging was used to examine these fundamental relationships. In CL spectrum imaging we collect a spectrum per pixel in a 256 x 256 pixel SEM image by synchronizing a cryogenic silicon charge-coupled device with the electron-beam positioning. High spatial resolution photon energy maps obtained with this technique can reveal intricate luminescence phenomena that are not apparent in spectroscopic data. CL spectrum imaging was performed at T= 25 K on the back surface of CSS-deposited CdTe thin-films in a CdTe/CdS/SnO_2/glass configuration without back contacting. Both as-deposited and CdCl2 vapor-treated samples were analyzed. Luminescence emission is detected (bands) at ~1.32 eV and ~1.50 eV, which are consistent with Z- and Y-bands. The importance of the Z-band to CdTe solar cells is discussed. For the grains in the as-deposited films, there is a significant redshift in the transition energies near the grain boundaries. For the Z-band, this behavior is due to the effect of the high GB recombination velocity (sX~1x10 4 cm/s) in as-deposited CSS films on the donor-acceptor pair transition mechanism. The concentration of the shallow donor species participating in the Z-band transition was estimated to be ~1017 cm-3 . Based on this estimate, and the spatial correlation between the Z-band and the A-center (VCd-ClTe) complex transitions, ClTe is proposed as is the shallow donor species.

  20. Resetting the Defect Chemistry in CdTe

    Energy Technology Data Exchange (ETDEWEB)

    Metzger, Wyatt K.; Burst, James; Albin, David; Colegrove, Eric; Moseley, John; Duenow, Joel; Farrell, Stuart; Moutinho, Helio; Reese, Matt; Johnston, Steve; Barnes, Teresa; Perkins, Craig; Guthrey, Harvey; Al-Jassim, Mowafak

    2015-06-14

    CdTe cell efficiencies have increased from 17% to 21% in the past three years and now rival polycrystalline Si [1]. Research is now targeting 25% to displace Si, attain costs less than 40 cents/W, and reach grid parity. Recent efficiency gains have come largely from greater photocurrent. There is still headroom to lower costs and improve performance by increasing open-circuit voltage (Voc) and fill factor. Record-efficiency CdTe cells have been limited to Voc <; 880 mV, whereas GaAs can attain Voc of 1.10 V with a slightly smaller bandgap [2,3]. To overcome this barrier, we seek to understand and increase lifetime and carrier concentration in CdTe. In polycrystalline structures, lifetime can be limited by interface and grain-boundary recombination, and attaining high carrier concentration is complicated by morphology.

  1. A Quaternary ZnCdSeTe Nanotip Photodetector

    Directory of Open Access Journals (Sweden)

    Cheng YC

    2009-01-01

    Full Text Available Abstract The authors report the growth of needle-like high density quaternary Zn0.87Cd0.13Se0.98Te0.02nanotips on oxidized Si(100 substrate. It was found that average length and average diameter of the nanotips were 1.3 μm and 91 nm, respectively. It was also found that the as-grown ZnCdSeTe nanotips exhibit mixture of cubic zinc-blende and hexagonal wurtzite structures. Furthermore, it was found that the operation speeds of the fabricated ZnCdSeTe nanotip photodetector were fast with turn-on and turn-off time constants both less than 2 s.

  2. Studies of recrystallization of CdTe thin films after CdCl{sub 2} treatment

    Energy Technology Data Exchange (ETDEWEB)

    Moutinho, H.R.; Al-Jassim, M.M.; Abulfotuh, F.A.; Levi, D.H.; Dippo, P.C.; Dhere, R.G.; Kazmerski, L.L. [National Renewable Energy Lab., Golden, CO (United States)

    1997-12-31

    CdTe thin films deposited by physical vapor deposition (PVD) and close-spaced sublimation (CSS) have been treated with CdCl{sub 2} at 350 and 400 C. Atomic force microscopy (AFM) analysis showed that the films started recrystallizing during the 350 C CdCl{sub 2} treatment. These results were confirmed by the presence of two lattice parameters, detected in X-ray diffraction (XRD) analysis. The PVD films treated at 400 C were completely recrystallized and grain growth was observed. The formation of Cd(S{sub 1{minus}x}Te{sub x}) alloy in these films was evidenced by the appearance of extra peaks close to the CdTe peaks in the diffraction patterns. No major changes were observed in the structural properties of CSS CdTe films treated at the same conditions. It was concluded that the effect of the CdCl{sub 2} treatment in the CdTe films is to promote recrystallization and grain growth, but only if enough lattice-strain energy is available (as is the case for PVD films). Time-resolved photoluminescence (TRPL) analysis showed, for PVD and CSS films, an increase in minority-carrier lifetime with the treatment, mainly at 400 C, probably due to elimination of deep levels within the band gap.

  3. MBE HgCdTe for HDVIP Devices: Horizontal Integration in the US HgCdTe FPA Industry

    Science.gov (United States)

    Aqariden, F.; Elsworth, J.; Zhao, J.; Grein, C. H.; Sivananthan, S.

    2012-10-01

    Molecular beam epitaxy (MBE) growth of HgCdTe offers the possibility of fabricating multilayer device structures with an almost unlimited choice of infrared sensor designs for focal-plane array (FPA) fabrication. HgCdTe offers two major advantages that explain its dominance in the infrared photon detector marketplace. The thermal generation rate per unit volume of the material is lower and the quantum efficiency for photon absorption in the infrared is higher in HgCdTe than in any competing material—it yields devices with quantum efficiencies as high as 0.99. Recently, EPIR Technologies and DRS Infrared Technologies agreed to collaborate and examine: (i) the feasibility of employing MBE HgCdTe in the fabrication of high-density vertically interconnected photodiodes (HDVIPs), which are usually fabricated with liquid-phase epitaxy material, and (ii) the potential benefits of horizontal integration, with EPIR supplying the MBE materials to DRS for device and array fabrication. The team designed and developed passivation-absorber-passivation structures that are heavily used by DRS. This paper provides an overview of the characteristics of HDVIP devices and arrays fabricated from MBE HgCdTe and the anticipated advantages of horizontal integration in the industry. Material growth, device fabrication, and test results are presented.

  4. Comparative study of Hg xCd 1-xTe films grown on CdTe thin films previously deposited from two different techniques

    Science.gov (United States)

    Ali, A.; Abbas Shah, N.; Maqsood, A.

    2009-04-01

    High quality cadmium telluride (CdTe) thin films were grown on glass substrates with two different techniques, two evaporation source (TES) and closed space sublimation (CSS). Further to the above mercury telluride (HgTe) was then deposited by using single source on both CdTe thin films for obtaining Hg xCd 1-xTe samples. The crystalline structure of the Hg xCd 1-xTe sample grown from CSS-CdTe showed the preferential (1 1 1) orientation with smoother and larger grain size than those of TES-CdTe. The optical transmission for TES-CdTe sample was above 90% in the 1000-1500 nm range whereas it was significantly below 80% for CSS-CdTe sample. The optical transmission for TES-Hg xCd 1-xTe and CSS-Hg xCd 1-xTe was ˜60%. The resistivity at room temperature of TES-CdTe and CSS-CdTe was ˜3.33×10 9 Ω cm and ˜2.20×10 8 Ω cm, respectively, while the resistivity of TES-Hg xCd 1-xTe and CSS-Hg xCd 1-xTe samples was ˜1.73 Ω cm and ˜5.34×10 5 Ω cm, respectively. The comparative study of ternary compound prepared with the above techniques has been carried out for the first time.

  5. Preparation and multicolored fluorescent properties of CdTe quantum dots/polymethylmethacrylate composite films

    Energy Technology Data Exchange (ETDEWEB)

    Huang, Yanni; Liu, Jianjun, E-mail: jjliu717@aliyun.com; Yu, Yingchun; Zuo, Shengli

    2015-10-25

    A new simple route was presented for the preparation of stable fluorescent CdTe/polymethylmethacrylate (CdTe/PMMA) composite films by using hydrophilic thioglycolic acid capped CdTe quantum dots (TGA-CdTe QDs) and polymethylmethacrylate (PMMA) as raw materials. The TGA-CdTe QDs were firstly exchanged with n-dodecanethiol (DDT) to become hydrophobic DDT-CdTe QDs via a ligand exchange strategy, and then incorporated into PMMA matrix to obtain fluorescent CdTe/PMMA composite films. The structure and optical properties of DDT-CdTe QDs and CdTe/PMMA composite films were investigated by XRD, IR, UV and PL techniques. The results indicated that the obtained DDT-CdTe QDs well preserved the intrinsic structure and the maximum emission wavelength of the initial water-soluble QDs and the resulting 6.10 wt% CdTe/PMMA composite film exhibited significantly enhanced PL intensity. Furthermore, the multicolored composite films with green, yellow-green, yellow and orange light emissions were well tuned by incorporating the CdTe QDs of various maximum emission wavelengths. The TEM image demonstrated that the CdTe QDs were well-dispersed in the PMMA matrix without aggregation. Superior photostability of QDs in the composite film was confirmed by fluorescence lifetime measurement. Thermo-gravimetric analysis of CdTe/PMMA composite films showed no obvious enhancement of thermal stability compared with pure PMMA. - Highlights: • Ligand-exchange strategy was used to render CdTe QDs oil-soluble. • CdTe QDs were incorporated into PMMA matrix to fabricate fluorescent films. • The resulting 6.10 wt% CdTe/PMMA film exhibited significantly enhanced PL intensity. • Fluorescent colors of films were tuned by varying the λ{sub em} of incorporated CdTe QDs.

  6. Synthesis and characterization of Sn-doped CdZnS nanoparticles

    Indian Academy of Sciences (India)

    R Shrivastava; S C Shrivastava

    2015-09-01

    Tin (Sn)-doped cadmium zinc sulphide nanoparticles (CdZnS : Sn) were synthesized by the chemical bath deposition method with two different concentrations of Sn (2 and 4 mol%). X-ray diffraction (XRD) pattern reveals the formation of CdZnS nanoparticles with cubic and hexagonal structure. It was observed that the presence of Sn does not alter the structure of CdZnS. Average crystallite size was measured from XRD data by using Scherrer’s formula. From the study of absorption spectra, band-to-band absorption was obtained at 460 and 490 nm, respectively, for the Sn-doped (2 and 4 mol%) CdZnS nanoparticles. Energy bandgap for undoped and Sn-doped CdZnS varies from 3.5 to 2.9 eV with error ± 0.05 eV. The presence of Sn was confirmed by energy-dispersive X-ray analysis. The effect of dopant concentration on the photoluminescence (PL) intensity has also been studied. The PL emission peak has been observed at 540, 550 and 560 nm for the Sn-doped (CdZnS, CdZnS 2 mol% and CdZnS 4 mol%), respectively, nanoparticles. XRD and PL analyses demonstrate that the Sn2+ ions uniformly substitute Cd2+ sites or interstitial sites in CdZnS lattice, which influence the optical properties. Increase in the concentration of Sn shifts the UV–vis absorption spectra and PL emission spectra towards higher wavelength side. Particle size and the crystallinity of CdZnS : Sn nanoparticles were confirmed through atomic force microscopy.

  7. CdTe nano-structures for photovoltaic devices

    OpenAIRE

    Corregidor, V.; Alves, L. C.; FRANCO, N.; Barreiros, Maria Alexandra; Sochinskii, N. V.; Alves, E

    2013-01-01

    CdTe nano-structures with diameter of ∼100 nm and variable length (200–600 nm) were fabricated on glass substrates covered with conductive buffer layers such as NiCr, ZAO (ZnO:Al2O3 + Ta2O5) or TiPd alloys. The fabrication process consisted of the starting vapour deposition of metal catalyst dropped layer followed by the isothermal catalyst-prompted vapour growth of CdTe nano-structured layer of controllable shape and surface filling. The effect of buffer layers on the crystallographic orient...

  8. Optical measurements for excitation of CdTe quantum dots

    Science.gov (United States)

    Vladescu, Marian; Feies, Valentin; Schiopu, Paul; Craciun, Alexandru; Grosu, Neculai; Manea, Adrian

    2016-12-01

    The paper presents the experimental results obtained using a laboratory setup installation for fluorescence excitation of CdTe QDs used as biomarkers for clinical diagnostics. Quantum Dots (QDs) made of Cadmium Telluride (CdTe), are highly fluorescent and they are used as robust biomarkers. Generally, QDs are referred to as the zero-dimensional colloidal crystals that possess strong size dependence and multi-colored luminescence properties. Along with its intrinsic features, such as sharp and symmetric emission, photo-stability and high quantum yields, QDs play a vital role in various applications, namely the identification of the chemical moieties, clinical diagnostics, optoelectronics, bio-imaging and bio-sensing1.

  9. Crystal Growth of Solid Solution HgCdTe Alloys

    Science.gov (United States)

    Lehoczky, Sandor L.

    1997-01-01

    The growth of homogenous crystals of HgCdTe alloys is complicated by the large separation between their liquidus and solidus temperatures. Hg(1-x)Cd(x)Te is representative of several alloys which have electrical and optical properties that can be compositionally tuned for a number of applications. Limitations imposed by gravity during growth and results from growth under reduced conditions are described. The importance of residual accelerations was demonstrated by dramatic differences in compositional distribution observed for different attitudes of the space shuttle that resulted in different steady acceleration components.

  10. A carbon dots-CdTe quantum dots fluorescence resonance energy transfer system for the analysis of ultra-trace chlortoluron in water.

    Science.gov (United States)

    Tao, Huilin; Liao, Xiufen; Sun, Chao; Xie, Xiangli; Zhong, Fuxin; Yi, Zhongsheng; Huang, Yipeng

    2015-02-05

    In this paper, a fluorescence resonance energy transfer (FRET) system between fluorescence carbon dots (CDs, donor) and CdTe quantum dots (CdTe, acceptor) was constructed, and a novel platform for sensitive and selective determination of chlortoluron was accordingly proposed. It was found that in Tris-HCl buffer solution at pH=8.7, energy transfer from CDs to CdTe occurred, which resulted in a great enhancement of the fluorescence intensity of CdTe. Upon the addition of chlortoluron, in terms of strong interaction between chlortoluron and CdTe QDs through the formation of chlortoluron-CdTe ground state complex, resulted in CdTe fluorescence quenching. Under optimal conditions, in range of 2.4×10(-10)molL(-1)-8.5×10(-8)molL(-1), the change of CdTe fluorescence intensity was in good linear relationship with the chlortoluron concentration, and the detection limit was 7.8×10(-11)molL(-1) (S/N=3). Most of common relevant substance, cations and anions did not interfere with the detection of chlortoluron. The proposed method was applied to determine chlortoluron in water samples with satisfactory results.

  11. Microstructure of absorber layers in CdTe/CdS solar cells

    CERN Document Server

    Cousins, M A

    2001-01-01

    expected from extrapolating the linear trend in the bulk. These observations are explained in terms of the pinning of the CdTe grain size to the underlying CdS, and the small grain size this causes. A simple model was proposed for a link between the grain-growth to the efficiency improvement. The study also examines the behaviour of defects within grains upon CdCl sub 2 treatment provided the first direct evidence of recovery on CdCl sub 2 treatment in this system. Finally, a computer model is presented to describe the evolution of microstructure during growth. This is shown to be capable of reproducing the observed variation in grain size, but its strict physical accuracy is questioned. This work concerns the microstructure of CSS-grown CdTe layers used for CdTe/CdS solar cells. Particular attention is given to how the development of microstructure on annealing with CdCl sub 2 may correlate with increases in efficiency. By annealing pressed pellets of bulk CdTe powder, it is shown that microstructural change...

  12. Emitter Choice for Epitaxial CdTe Solar Cells

    Energy Technology Data Exchange (ETDEWEB)

    Song, Tao; Kanevce, Ana; Sites, James R.

    2016-11-21

    High-quality epitaxial CdTe layers with low defect density and high carrier concentration have been demonstrated by several research groups. Nevertheless, one primary challenge for high-performance epitaxial CdTe solar cells is how to choose a suitable emitter partner for the junction formation. The numerical simulations show that a type I heterojunction with small conduction band offset (0.1 eV = ..delta..Ec = 0.3 eV) is necessary to maintain a good cell efficiency even with large interface recombination. Otherwise, a small 'cliff' can assist interface recombination causing smaller Voc, and a large 'spike' (..delta..Ec = 0.4 eV) can impede the photo current and lead to a reduction of JSC and FF. Among the three possible emitters, CdS, CdMgTe, and MgZnO, CdMgTe (with ~30% Mg) and MgZnO (with ~ 20% Mg) are likely to be a better choice since their type-I junction can tolerate a larger density of interface defects.

  13. Photocurrent mapping of 3D CdSe/CdTe windowless solar cells.

    Science.gov (United States)

    Hangarter, Carlos M; Debnath, Ratan; Ha, Jong Y; Sahiner, Mehmet A; Reehil, Christopher J; Manners, William A; Josell, Daniel

    2013-09-25

    This paper details the use of scanning photocurrent microscopy to examine localized current collection efficiency of thin-film photovoltaic devices with in-plane patterning at a submicrometer length scale. The devices are based upon two interdigitated comb electrodes at the micrometer length scale prepatterned on a substrate, with CdSe electrodeposited on one electrode and CdTe deposited over the entire surface of the resulting structure by pulsed laser deposition. Photocurrent maps provide information on what limits the performance of the windowless CdSe/CdTe thin-film photovoltaic devices, revealing "dead zones" particularly above the electrodes contacting the CdTe which is interpreted as recombination over the back contact. Additionally, the impact of ammonium sulfide passivation is examined, which enables device efficiency to reach 4.3% under simulated air mass 1.5 illumination.

  14. Device analysis methods for physical cell parameters of CdTe/CdS solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Baetzner, D.L. [Eidgenoessische Technische Hochschule, Zurich (Switzerland). Inst. fuer Quantenelektronik; Oezsan, M.E. [BP Solar Technology Centre, Sunbury-on-Thames, Middlesex (United Kingdom); Bonnet, D. [ANTEC Angewandte Neue Technologien GmbH, Kelkheim (Germany); Buecher, K. [Fraunhofer-Institut fuer Solare Energiesysteme (ISE), Freiburg im Breisgau (Germany). Abt. Thermische und Optische Systeme

    2000-02-21

    CdTe/CdS solar cells are thin film solar cells made of several different materials. As front contact serves a TCO, the p-n junction is an intermixed CdS/CdTe heterojunction and the metallization on the CdTe layer, which is needed for the back contact, usually shows a Schottky diode behaviour. Therefore the optoelectrical properties of the cells are complex and can often not be explained straight forward like in silicon solar cells. In order to determine the physical cell parameters like the Schottky barrier height and the minority carrier diffusion length in the absorber layer, we investigated the temperature dependence of the dark I-V characteristics and the spectral response. By modelling the temperature and wavelength dependence of the cell parameters, physical quantities such as the barrier height of the Schottky contact can be determined. (orig.)

  15. Doping and Diffusion in HgCdTe

    Science.gov (United States)

    1991-01-28

    In’i, -InT. Te - 1.8 ( - 3 .5 )h ( + 2.9 - 6/) TeT1’- Tej . 4 Hg rich HgCdTe Hg - 1.8 + 1.2 + 1.4 - 2p H - ’g, - H g j.. ’TI - tetrahedral position...A. Anderson, Appl. Phys. Lett. 53, 11.81 (1988). B. D. Patterson, Rev. Mod. Phys. 60, 69 (1988). 60 V. A. Singh , C. Weigel, J. W. Corbett, and L. M

  16. Optimizing the superconducting transition temperature and upper critical field of Sn1-xInxTe

    Science.gov (United States)

    Zhong, R. D.; Schneeloch, J. A.; Shi, X. Y.; Xu, Z. J.; Zhang, C.; Tranquada, J. M.; Li, Q.; Gu, G. D.

    2013-07-01

    Sn1-xInxTe is a possible candidate for topological superconductivity. Previous work has shown that substitution of In for Sn in the topological crystalline insulator SnTe results in superconductivity, with the transition temperature, Tc, growing with In concentration. We have performed a systematic investigation of Sn1-xInxTe for a broad range of x, synthesizing single crystals (by a modified floating-zone method) as well as polycrystalline samples. The samples have been characterized by x-ray diffraction, resistivity, and magnetization. For the single crystals, the maximum Tc is obtained at x=0.45 with a value of 4.5 K, as determined by the onset of diamagnetism.

  17. CdS/CdSe co-sensitized SnO2 photoelectrodes for quantum dots sensitized solar cells

    Science.gov (United States)

    Lin, Yibing; Lin, Yu; Meng, Yongming; Tu, Yongguang; Zhang, Xiaolong

    2015-07-01

    SnO2 nanoparticles were synthesized by hydrothermal method and applied to photo-electrodes of quantum dots-sensitized solar cells (QDSSCs). After sensitizing SnO2 films via CdS quantum dots, CdSe quantum dots was decorated on the surface of CdS/SnO2 photo-electrodes to further improve the power conversion efficiency. CdS and CdSe quantum dots were deposited by successive ionic layer absorption and reaction method (SILAR) and chemical bath deposition method (CBD) respectively. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) were used to identify the surface profile and crystal structure of SnO2 photo-electrodes before and after deposited quantum dots. After CdSe co-sensitized process, an overall power conversion efficiency of 1.78% was obtained in CdSe/CdS/SnO2 QDSSC, which showed 66.4% improvement than that of CdS/SnO2 QDSSC.

  18. High-efficiency large-area CdTe panels

    Energy Technology Data Exchange (ETDEWEB)

    Albright, S.P.; Chamberlin, R.R.; Jordan, J.F. (Photon Energy, Inc., El Paso, TX (USA))

    1990-11-01

    The objective of this three year effort has been to develop an improved materials technology and fabrication process for limited volume production of 1 ft{sup 2} and 4 ft{sup 2} CdS/CdTe photovoltaic modules. The module stability objective by the end of this three year subcontract was to develop techniques to provide ten year life exploration with no greater than 10% degradation. In order to achieve these efficiency and stability objectives, the research program has been separated into tasks including: (1) analysis and characterization of CdS/CdTe Devices; (2) performance optimization on small cells; (3) encapsulation and stability testing; and (4) module efficiency optimization. 27 refs., 18 figs., 3 tabs.

  19. Influence of Sn concentration on the physical properties of CdO:Sn thin films deposited by spray pyrolysis

    Energy Technology Data Exchange (ETDEWEB)

    Vigil-Galan, O.; Ruiz, C.M. [Departamento de Fisica de Materiales, Universidad Autonoma de Madrid, 28049 Madrid (Spain); Sanchez-Gonzalez, Y. [EMPROTEL, Copextel, Carretera Prensa Latina km 111/2, Marianao, La Habana (Cuba); Arias-Carbajal, A. [Facultad de Quimica-IMRE, Universidad de La Habana, 10400 La Habana (Cuba); Contreras-Puente, G.; Tufino-Velazquez, M. [Escuela Superior de Fisica y Matematicas, Instituto Politecnico Nacional, 07738 Mexico, D.F. (Mexico)

    2006-12-15

    Sn doped cadmium oxide thin films were prepared on glass substrates by the spray pyrolysis (SP) method from a cadmium acetate aqueous solution. The Sn (IV) concentration in the solution was varied up to 2 wt%, keeping constant the other growth parameters. The structural, electrical and optical properties of the films were studied as a function of Sn concentration. The best results were obtained for CdO films doped with 1% Sn nominal concentration. The properties of these films are influenced by the air annealing performed at 450 C for 30-120 min. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  20. Characterization of CdS Thin-Film in High Efficient CdS/CdTe Solar Cells

    Science.gov (United States)

    Tsuji, Miwa; Aramoto, Tetsuya; Ohyama, Hideaki; Hibino, Takeshi; Omura, Kuniyoshi

    2000-07-01

    Cadmium sulfide (CdS) thin films are the most commonly used window materials for high efficient cadmium telluride (CdTe) and chalcopyrite polycrystalline thin-film photovoltaic devices. High efficient CdS/CdTe solar cells with thin CdS films have been developed using ultrathin CdS films with a thickness of less than 0.1 μm. CdS films were deposited on transparent conductive oxide (TCO)/glass substrates by the metal organic chemical vapor deposition (MOCVD) technique. CdTe films were subsequently deposited by the close-spaced sublimation (CSS) technique. The screen printing and sintering method fabricated carbon and silver electrodes. Cell performance depends primarily on the electrical and optical properties of CdS films. Therefore we started to develop higher-quality CdS films and found clear differences between high- and low-quality CdS films from the analyses of scanning electron microscope (SEM), atomic force microscope (AFM), secondary ion mass spectroscopy (SIMS), thermal desorption spectrometry (TDS) and Fourier transforms-infrared spectrometry (FT-IR) measurements. As a result of controlling the quality of CdS films, a photovoltaic conversion efficiency of 10.5% has been achieved for size of 1376 cm2 of the solar cells under the Air Mass (AM) 1.5 conditions of the Japan Quality Assurance Organization.

  1. Identification of Ag-acceptors in $^{111}\\!$Ag $^{111}\\!$Cd doped ZnTe and CdTe

    CERN Document Server

    Hamann, J; Deicher, M; Filz, T; Lany, S; Ostheimer, V; Strasser, F; Wolf, H; Wichert, T

    2000-01-01

    Nominally undoped ZnTe and CdTe crystals were implanted with radioactive $^{111}\\!$Ag, which decays to $^{111}\\!$Cd, and investigated by photoluminescence spectroscopy (PL). In ZnTe, the PL lines caused by an acceptor level at 121 meV are observed: the principal bound exciton (PBE) line, the donor-acceptor pair (DAP) band, and the two-hole transition lines. In CdTe, the PBE line and the DAP band that correspond to an acceptor level at 108 meV appear. Since the intensities of all these PL lines decrease in good agreement with the half-life of $^{111}\\!$Ag of 178.8 h, both acceptor levels are concluded to be associated with defects containing a single Ag atom. Therefore, the earlier assignments to substitutional Ag on Zn- and Cd-lattice sites in the respective II-VI semiconductors are confirmed. The assignments in the literature of the S$_1$, S$_2$, and S$_3$ lines in ZnTe and the X$\\scriptstyle^\\textrm{Ag}_{1}\\,\\,,$ X$\\scriptstyle^\\textrm{Ag}_{2}$/ C$\\scriptstyle^\\textrm{Ag}_{1}\\,$ and C$\\scriptstyle^\\textrm{...

  2. Degradation mechanisms studies in CdS/CdTe solar cells with ZnTe:Cu/Au back contact

    Science.gov (United States)

    Morgan, D.; Tang, J.; Kaydanov, V.; Ohno, T. R.; Trefny, J. U.

    1999-03-01

    CdS/CdTe/ZnTe:Cu/Au solar cells were fabricated and tested under stressed conditions including enhanced temperature, forward and reverse bias, open circuit, dark and light. Discussion of results was focused mostly on the development of the back contact Schottky diode (increase in series resistance). Changes in the cell parameters were detected based on the analysis of the dynamic resistance of a cell (dV/dJ) at forward biases. A possible role of electromigration of the Cu dopant was discussed.

  3. Degradation mechanisms studies in CdS/CdTe solar cells with ZnTe:Cu/Au back contact

    Energy Technology Data Exchange (ETDEWEB)

    Morgan, D.; Tang, J.; Kaydanov, V.; Ohno, T.R.; Trefny, J.U. [Department of Physics, Colorado School of Mines, Golden, Colorado 80401 (United States)

    1999-03-01

    CdS/CdTe/ZnTe:Cu/Au solar cells were fabricated and tested under stressed conditions including enhanced temperature, forward and reverse bias, open circuit, dark and light. Discussion of results was focused mostly on the development of the back contact Schottky diode (increase in series resistance). Changes in the cell parameters were detected based on the analysis of the dynamic resistance of a cell (dV/dJ) at forward biases. A possible role of electromigration of the Cu dopant was discussed. {copyright} {ital 1999 American Institute of Physics.}

  4. Effects of processing temperature on the thickness of CdS and the performance of CdTe solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Ferekides, C.S.; Tetali, B.; Marinskiy, D.; Marinskaya, S.; Morel, D. [Department of Electrical Engineering, Center for Clean Energy and Vehicles, University of South Florida, Tampa, Florida 33620 (United States)

    1997-02-01

    CdTe cells have been fabricated on soda lime glass substrates. The effect of the CdS thickness and CdTe deposition temperature on the spectral response (SR) and solar cell parameters has been studied. The CdTe deposition temperature has been found to be a key processing parameter in determining the extent of interdiffusion at the CdTe and CdS interface. When the deposition of CdTe is carried out at high temperatures a significant portion of the CdS films is {open_quotes}lost{close_quotes} due to interdiffusion which leads to enhancement of the blue response of the solar cells. Devices with identical blue response (400{endash}500 nm) have been fabricated even though the starting CdS thicknesses were different; the cells for which the starting CdS thickness was greater exhibited higher open-circuit voltages and fill factors. {copyright} {ital 1997 American Institute of Physics.}

  5. New μ-SnTe{sub 4} and μ-Sn{sub 2}Te{sub 6} ligands to transition metal: Solvothermal syntheses and characterizations of zinc tellurostannates containing polyamine ligands

    Energy Technology Data Exchange (ETDEWEB)

    Lu, Jialin; Wang, Fang; Shen, Yali; Tang, Chunying; Zhang, Yong; Jia, Dingxian, E-mail: jiadingxian@suda.edu.cn

    2014-08-15

    Zinc tellurostannates [(Zn(teta)){sub 2}(μ-1κ:2κ-SnTe{sub 4})] (1), [(Zn(teta)){sub 3}(μ{sub 3}-1κ:2κ:3κ-SnTe{sub 4})]I{sub 2} (2), [(Zn(tren)){sub 2}(μ-1κ:2κ-Sn{sub 2}Te{sub 6})] (3), and [Zn(dien){sub 2}]{sub 4}(Sn{sub 2}Te{sub 6}){sub 1.75}(Sn{sub 2}Te{sub 8}){sub 0.25}·dien (4) were prepared by the reactions of Zn, Sn, and Te with iodine ion assistant in teta and dien. The tetrahedral [SnTe{sub 4}]{sup 4−} anion coordinates to two [Zn(teta)]{sup 2+} units as a bidentate μ-1κ:2κ-SnTe{sub 4} ligand to form the neutral complex 1. It coordinates to three [Zn(teta)]{sup 2+} units with a tridentate μ{sub 3}-1κ:2κ:3κ coordination modes, generating a complex cation [(Zn(teta)){sub 3}(μ{sub 3}-1κ:2κ:3κ- SnTe{sub 4})]{sup 2+} in 2. In 3, the [Sn{sub 2}Te{sub 6}]{sup 4−} anion joins two [Zn(tren)]{sup 2+}cations with the trans terminal Te atoms, forming neutral complex 3. The μ-1κ:2κ-SnTe{sub 4}, μ{sub 3}-1κ:2κ:3κ-SnTe{sub 4}, and μ-1κ:2κ-Sn{sub 2}Te{sub 6} ligands to TM centers in 1–3 have not been observed before. Compound 4 contains a normal [Sn{sub 2}Te{sub 6}]{sup 4−} and an abnormal [(Sn{sub 2}Te{sub 6}){sub 0.75}(Sn{sub 2}Te{sub 8}){sub 0.25}]{sup 4−} anions. Compounds 1–4 exhibit narrow band gaps in the range of 1.47–1.98 eV, and a distinct red-shift of the band gaps is observed from 4 to 1−3. - Graphical abstract: Zinc tellurostannates were prepared with iodine ion assistant in polyamines, and first μ-1κ:2κ-SnTe{sub 4}, μ{sub 3}-1κ:2κ:3κ-SnTe{sub 4}, and μ-1κ:2κ-Sn{sub 2}Te{sub 6} ligands TM centers were obtained. - Highlights: • Zinc-tellurostannates were first prepared with iodine ion assistant. • Novel μ-1κ:2κ-SnTe{sub 4}, μ{sub 3}-1κ:2κ:3κ-SnTe{sub 4}, and μ-1κ:2κ-Sn{sub 2}Te{sub 6} ligands were obtained. • The Zinc tellurostannates exhibit optical bandgaps between 1.47 and 1.98 eV.

  6. Optimized conditions for the improvement of thin film CdS/CdTe solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Mohamed, H.A., E-mail: hussein_abdelhafez2000@yahoo.com

    2015-08-31

    Efficient thin film CdS/CdTe solar cell performance requires optimum parameters of each layer of this cell and of the barrier structure. Moreover, the effect of optical losses, recombination losses at front and back surface of CdTe and recombination losses in the space-charge region (SCR) must be considered in order to really analyze the role of these parameters on the performance of these cells. This work is focused on studying theoretically the effect of the thickness of the front contact (ITO), thickness of the window layer (CdS), thickness of the absorber layer (CdTe), width of the space-charge region and electron lifetime on the efficiency of CdS/CdTe solar cells. The reflection losses from interfaces and absorption losses in ITO and CdS, front and rear surface recombination losses of CdTe as well as recombination losses in SCR have been studied. It has been observed that the short-circuit current strongly depends on the thickness of ITO, thickness of CdS, thickness CdTe and electron lifetime. The concentration of uncompensated impurities (N{sub a} − N{sub d}) in CdTe, which determines the width of SCR, plays a key role in the generation of photocurrent. The recombination losses in the SCR decrease rapidly with increasing the carrier lifetime in this region and can be ignored at lifetime of 10{sup −7} s. The reflectivity from the back contact introduces a small influence in increasing the short-current density particularly at thick absorber layer (5–8 μm). Under the conditions of N{sub a} − N{sub d} ~ 10{sup 16} cm{sup −3}, τ{sub n} = 10{sup −6} s, d{sub CdTe} = 8 μm, d{sub ITO} = 100 nm, and d{sub CdS} = 100 nm, the recombination and optical losses record their minimum ratio of 27%. Most of these losses (24%) are due to the optical losses. The efficiency of CdS/CdTe under these parameters is about 18.2% which is exactly matching with the recent experimental studies. Moreover, an ultrathin CdTe (= 1 μm) is sufficient to introduce high

  7. Electrical Characterization of Cu Composition Effects in CdS/CdTe Thin-Film Solar Cells with a ZnTe:Cu Back Contact: Preprint

    Energy Technology Data Exchange (ETDEWEB)

    Li, J. V.; Duenow, J. N.; Kuciauskas, D.; Kanevce, A.; Dhere, R. G.; Young, M. R.; Levi, D. H.

    2012-07-01

    We study the effects of Cu composition on the CdTe/ZnTe:Cu back contact and the bulk CdTe. For the back contact, its potential barrier decreases with Cu concentration while its saturation current density increases. For the bulk CdTe, the hole density increases with Cu concentration. We identify a Cu-related deep level at {approx}0.55 eV whose concentration is significant when the Cu concentration is high. The device performance, which initially increases with Cu concentration then decreases, reflects the interplay between the positive influences and negative influences (increasing deep levels in CdTe) of Cu.

  8. Simulation of charge transport in pixelated CdTe

    Science.gov (United States)

    Kolstein, M.; Ariño, G.; Chmeissani, M.; De Lorenzo, G.

    2014-12-01

    The Voxel Imaging PET (VIP) Pathfinder project intends to show the advantages of using pixelated semiconductor technology for nuclear medicine applications to achieve an improved image reconstruction without efficiency loss. It proposes designs for Positron Emission Tomography (PET), Positron Emission Mammography (PEM) and Compton gamma camera detectors with a large number of signal channels (of the order of 106). The design is based on the use of a pixelated CdTe Schottky detector to have optimal energy and spatial resolution. An individual read-out channel is dedicated for each detector voxel of size 1 × 1 × 2 mm3 using an application-specific integrated circuit (ASIC) which the VIP project has designed, developed and is currently evaluating experimentally. The behaviour of the signal charge carriers in CdTe should be well understood because it has an impact on the performance of the readout channels. For this purpose the Finite Element Method (FEM) Multiphysics COMSOL software package has been used to simulate the behaviour of signal charge carriers in CdTe and extract values for the expected charge sharing depending on the impact point and bias voltage. The results on charge sharing obtained with COMSOL are combined with GAMOS, a Geant based particle tracking Monte Carlo software package, to get a full evaluation of the amount of charge sharing in pixelated CdTe for different gamma impact points.

  9. Intracavity CdTe modulators for CO2 lasers.

    Science.gov (United States)

    Kiefer, J. E.; Nussmeier, T. A.; Goodwin, F. E.

    1972-01-01

    The use of cadmium telluride as an electrooptic material for intracavity modulation of CO2 lasers is described. Included are the predicted and measured effects of CdTe intracavity modulators on laser performance. Coupling and frequency modulation are discussed and experimental results compared with theoretically predicted performance for both techniques. Limitations on the frequency response of the two types of modulation are determined.

  10. The role of oxygen in CdS/CdTe solar cells deposited by close-spaced sublimation

    Energy Technology Data Exchange (ETDEWEB)

    Rose, D.H.; Levi, D.H.; Matson, R.J. [National Renewable Energy Lab., Golden, CO (United States)] [and others

    1996-05-01

    The presence of oxygen during close-spaced sublimation (CSS) of CdTe has been previously reported to be essential for high-efficiency CdS/CdTe solar cells because it increases the acceptor density in the absorber. The authors find that the presence of oxygen during CSS increases the nucleation site density of CdTe, thus decreasing pinhole density and grain size. Photoluminescence showed that oxygen decreases material quality in the bulk of the CdTe film, but positively impacts the critical CdS/CdTe interface. Through device characterization the authors were unable to verify an increase in acceptor density with increased oxygen. These results, along with the achievement of high-efficiency cells (13% AM1.5) without the use of oxygen, led the authors to conclude that the use of oxygen during CSS deposition of CdTe can be useful but is not essential.

  11. The role of oxygen in CdS/CdTe solar cells deposited by close-spaced sublimation

    Energy Technology Data Exchange (ETDEWEB)

    Rose, D.H.; Levi, D.H.; Matson, R.J.; Albin, D.S.; Dhere, R.G.; Sheldon, P. [National Renewable Energy Lab., Golden, CO (United States)

    1996-09-01

    The presence of oxygen during close-spaced sublimation (CSS) of CdTe has been previously reported to be essential for high-efficiency CdS/CdTe solar cells because it increases the acceptor density in the absorber. The authors find that the presence of oxygen during CSS increases the nucleation site density of CdTe, thus decreasing pinhole density and grain size. Photoluminescence showed that oxygen decreases material quality in the bulk of the CdTe film, but positively impacts the critical CdS/CdTe interface. Through device characterization they were unable to verify an increase in acceptor density with increased oxygen. These results, along with the achievement of high-efficiency cells (13% AM1.5) without the use of oxygen, led the authors to conclude that the use of oxygen during CSS deposition of CdTe can be useful but is not essential.

  12. Characterization of CdS thin film in high efficient CdS/CdTe solar cells

    Science.gov (United States)

    Tsuji, Miwa; Aramoto, Tetsuya; Ohyama, Hideaki; Hibino, Takeshi; Omura, Kuniyoshi

    2000-06-01

    Cadmium sulfide (CdS) thin film is the most commonly used window material for high-efficient cadmium telluride (CdTe) thin-film photovoltaic devices. High-efficient CdS/CdTe solar cells have been developed using ultra-thin CdS films having a thickness of below 0.1 μm. CdS film is deposited on transparent conductive oxide (TCO) film coated glass substrates by the metal organic chemical vapor deposition (MOCVD) technique, CdTe film is subsequently deposited by the close-spaced sublimation (CSS) technique. Finally, carbon and Ag-In electrodes are fabricated by the screen printing and sintering method. Cell performance depends primarily on the electrical and optical properties of CdS film, and hence we started to develop higher quality CdS film and found out clear differences between high- and low-quality CdS films from various analyses: SEM, AFM, SIMS, TDS and FT-IR. As a result of controlling qualities of CdS films, photovoltaic conversion efficiency of 10.5% has been achieved for a size of 1376 cm 2 of the solar module under air mass (AM) 1.5 conditions by the Japan Quality Assurance Organization (JQA).

  13. Indirect exchange interaction between magnetic impurities in the two-dimensional topological insulator based on CdTe/HgTe/CdTe quantum wells

    Science.gov (United States)

    Kurilovich, P. D.; Kurilovich, V. D.; Burmistrov, I. S.

    2016-10-01

    We study indirect exchange interaction between magnetic impurities in the (001) CdTe/HgTe/CdTe symmetric quantum well. We consider low temperatures and the case of the chemical potential placed in the energy gap of the two-dimensional quasiparticle spectrum. We find that the indirect exchange interaction is suppressed exponentially with the distance between magnetic impurities. The presence of inversion asymmetry results in oscillations of the indirect exchange interaction with the distance and generates additional terms which are noninvariant under rotations in the (001) plane. The indirect exchange interaction matrix has complicated structure with some terms proportional to the sign of the energy gap.

  14. Synthesis of CdTe Quantum Dots with Tunable Photoluminescence Using Tellurium Dioxide as Tellurium Source

    Institute of Scientific and Technical Information of China (English)

    刘声燕; 王益林; 杨昆; 周立亚

    2012-01-01

    A simple and convenient method has been developed for synthesis of water-soluble CdTe quantum dots (QDs) under ambient atmospheric conditions. In contrast to the traditional aqueous synthesis, green to red emitting CdTe QDs were prepared by using TeO2 to replace Te or AIzTe3 as tellurium source in this method. The influences of ex- perimental variables, including pH value, 3-mercaptopropionic acid (MPA)/Cd and Te/Cd molar ratios, on the emis- sion peak and photoluminescence (PL) quantum yield (QY) of the obtained CdTe QDs have been systematically investigated. Experimental results indicate that green to red emitting CdTe QDs with a maximum photolumines- cence quantum yield of 35.4% can be prepared at pH 11.3 and rt(Cd) : n(Te) : n(MPA)= 1 : 0.1 : 1.7.

  15. Studies of CdS/CdTe interface: Comparison of CdS films deposited by close space sublimation and chemical bath deposition techniques

    Energy Technology Data Exchange (ETDEWEB)

    Han, Jun-feng, E-mail: pkuhjf@bit.edu.cn [Institut des Matériaux Jean Rouxel (IMN), Université de Nantes, UMR CNRS 6502, 2 rue de la Houssinière, BP 32229, 44322 Nantes Cedex 3 (France); Institute of Materials Science, Darmstadt University of Technology, Petersenstr. 23, 64287 Darmstadt (Germany); School of Physics, Beijing Institute of Technology, Beijing 100081 (China); Fu, Gan-hua; Krishnakumar, V.; Schimper, Hermann-Josef [Institute of Materials Science, Darmstadt University of Technology, Petersenstr. 23, 64287 Darmstadt (Germany); Liao, Cheng [Department of Physics, Peking University, Beijing 100871 (China); Jaegermann, Wolfram [Institute of Materials Science, Darmstadt University of Technology, Petersenstr. 23, 64287 Darmstadt (Germany); Besland, M.P. [Institut des Matériaux Jean Rouxel (IMN), Université de Nantes, UMR CNRS 6502, 2 rue de la Houssinière, BP 32229, 44322 Nantes Cedex 3 (France)

    2015-05-01

    The CdS layers were deposited by two different methods, close space sublimation (CSS) and chemical bath deposition (CBD) technique. The CdS/CdTe interface properties were investigated by transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS). The TEM images showed a large CSS-CdS grain size in the range of 70-80 nm. The interface between CSS-CdS and CdTe were clear and sharp, indicating an abrupt hetero-junction. On the other hand, CBD-CdS layer had much smaller grain size in the 5-10 nm range. The interface between CBD-CdS and CdTe was not as clear as CSS-CdS. With the stepwise coverage of CdTe layer, the XPS core levels of Cd 3d and S 2p in CSS-CdS had a sudden shift to lower binding energies, while those core levels shifted gradually in CBD-CdS. In addition, XPS depth profile analyses indicated a strong diffusion in the interface between CBD-CdS and CdTe. The solar cells prepared using CSS-CdS yielded better device performance than the CBD-CdS layer. The relationships between the solar cell performances and properties of CdS/CdTe interfaces were discussed. - Highlights: • Studies of CdS deposited by close space sublimation and chemical bath deposition • An observation of CdS/CdTe interface by transmission electron microscope • A careful investigation of CdS/CdTe interface by X ray photoelectron spectra • An easier diffusion at the chemical bath deposition CdS and CdTe interface.

  16. Crystal and electronic structure of PbTe/CdTe nanostructures

    Directory of Open Access Journals (Sweden)

    Sankowski Piotr

    2011-01-01

    Full Text Available Abstract In this article, the authors reported a theoretical study of structural and electronic properties of PbTe inclusions in CdTe matrix as well as CdTe nano-clusters in PbTe matrix. The structural properties are studied by ab initio methods. A tight-binding model is constructed to calculate the electron density of states (DOS of the systems. In contrast to the ab initio methods, the latter allows studying nanostructures with diameters comparable to the real ones. The calculations show that both kinds of inclusions lead to changes of the DOS of the carriers near the Fermi level, which may affect optical, electrical and thermoelectric properties of the material. These changes depend on the size, shape, and concentration of inclusions.

  17. Cu-Related Recombination in CdS/CdTe Solar Cells

    Energy Technology Data Exchange (ETDEWEB)

    Demtsu, S. H.; Albin, D. S.; Sites, J. R.; Metzger, W. K.; Duda, A.

    2008-02-01

    Cu used in the back contact of CdS/CdTe solar cells is known to improve contact behavior and open-circuit voltage. A study of devices made with varying Cu amounts confirmed these observations. However, Cu was also found to be deleterious to current collection. Time-resolved photoluminescence measurements of CdTe devices show that carrier lifetime decreased with increased Cu concentration. Drive-level-capacitance-profiling and low-temperature photoluminescence suggest this decrease in lifetime was associated with increased recombination center density introduced by Cu in the CdTe layer. The resulting impact of increased Cu on device performance was a voltage-dependent collection of photogenerated carriers that reduced fill-factor.

  18. CdTe Thin Film Solar Cells and Modules Tutorial; NREL (National Renewable Energy Laboratory)

    Energy Technology Data Exchange (ETDEWEB)

    Albin, David S.

    2015-06-13

    This is a tutorial presented at the 42nd IEEE Photovoltaics Specialists Conference to cover the introduction, background, and updates on CdTe cell and module technology, including CdTe cell and module structure and fabrication.

  19. A comparative study of CdTe quantum dots and CdTe@SiO2 nanoparticles: fabrication and cytotoxicity in HEK293 cells.

    Science.gov (United States)

    Sadaf, Asma; Zeshan, Basit; Wang, Zhuyuan; Zhang, Ruohu; Xu, Shuhong; Wang, Chunlei; Yang, Jing; Cui, Yiping

    2012-09-01

    Quantum Dots have shown remarkable potentials in biomedical research. Herein, we reported the effects of CdTe quantum dots (QDs) and CdTe@SiO2 nanoparticles (NPs) on human embryonic kidney 293 (HEK 293A) cells with the aim of investigating their in vitro cytotoxicity. The CdTe@SiO2 particles were prepared by reverse microemulsion method. The structural morphology of the CdTe and hydrophilic silica-coated CdTe particles were characterized by transmission electron microscopy (TEM), ultraviolet-visible (UV-vis) spectrometry and photoluminescence (PL) spectrometry. The in vitro cytotoxicity of CdTe QDs and CdTe@SiO2 nanoparticles was assessed in 293A cells using standard MTT assay, western blot and fluorescent microscopy. The results showed that the CdTe and CdTe@SiO2 particles were relatively uniform with the diameter of about 3.8 nm, 75 nm respectively. The cell viability and the adhesion ability were similar to the control 293A cells. The level of the fibronectin protein expression was decreased with the increasing concentration of CdTe while the no effects were observed on expression of beta-actin in CdTe as well as CdTe@SiO2 treated cells even at highest concentration of 45 microg/mL which demonstrated their good biocompatibility to 293A cells. The results indicate that the CdTe@SiO2 nanoparticles are attractive candidates for biological imaging studies as expected.

  20. Schottky Barrier CdTe(Cl) Detectors for Planetary Missions

    Science.gov (United States)

    Eisen, Yosef; Floyd, Samuel

    2002-10-01

    Schottky barrier cadmium telluride (CdTe) radiation detectors of dimensions 2mm × 2mm × 1mm and segmented monolithic 3cm × 3 cm × 1mm are under study at GSFC for future NASA planetary instruments. These instruments will perform x-ray fluorescence spectrometry of the surface and monitor the solar x-ray flux spectrum, the excitation source for the characteristic x-rays emitted from the planetary body. The Near Earth Asteroid Rendezvous (NEAR) mission is the most recent example of such a remote sensing technique. Its x-ray fluorescence detectors were gas proportional counters with a back up Si PIN solar monitor. Analysis of NEAR data has shown the necessity to develop a solar x-ray detector with efficiency extending to 30keV. Proportional counters and Si diodes have low sensitivity above 9keV. Our 2mm × 2mm × 1mm CdTe operating at -30°C possesses an energy resolution of 250eV FWHM for 55Fe with unit efficiency to up to 30keV. This is an excellent candidate for a solar monitor. Another ramification of the NEAR data is a need to develop a large area detector system, 20-30 cm2, with cosmic ray charged particle rejection, for measuring the characteristic radiation. A 3cm × 3cm × 1mm Schottky CdTe segmented monolithic detector is under investigation for this purpose. A tiling of 2-3 such detectors will result in the desired area. The favorable characteristics of Schottky CdTe detectors, the system design complexities when using CdTe and its adaptation to future missions will be discussed.

  1. Preparation and properties of evaporated CdTe films compared with single crystal CdTe. Annual report, 1 February 1983-31 January 1984

    Energy Technology Data Exchange (ETDEWEB)

    Bube, R; Fahrenbruch, A; Huber, W; Fortmann, C; Thorpe, T

    1984-09-01

    Variation of CdS/CdTe/graphite thick film solar cell properties was investigated as a function of temperature for CdS film deposition. A maximum open-circuit voltage of 0.67 V was found for a deposition temperature of 160/sup 0/C, corresponding to a CdS film resistivity of 150 ohm-cm. The effect is not due to avoidance of higher temperature annealing of the CdTe film in higher temperature CdS film depositions nor to the diffusion of In from the outermost CdS: In layer. The effect of coating the graphite before CdTe deposition with Au or Cu was also investigated. Although high concentrations of both Au or Cu could be determined after CdTe deposition, CdTe films grown on this coated graphite had lower hole densities than films grown on uncoated graphite. Photovoltaic parameters of thin-film CdS/CdTe/graphite solar cells were investigated as a function of storage time to check the stability of these cells. Initial degradation of parameters (especially fill factor) could be reversed by heat treatment in hydrogen, with subsequent properties being stable. Heat treatment of CdS/CdTe/graphite solar cells in air increases cell resistivity and decreases fill factor; heat treatment in hydrogen produces the reverse effect. The hole density is not affected by these heat treatments, suggesting that effects are associated with grain boundaries in the film.

  2. Development of a CdTe/CdS solar wafer. Final report; Entwicklung einer CdTe/CdS Duennschicht-Solarzelle. Schlussbericht

    Energy Technology Data Exchange (ETDEWEB)

    Koentges, M.; Reineck-Koch, R.

    2002-07-01

    The focus was on the development and optimisation of the close-spaced sublimation process in an inline coating plant for production of stable high-efficiency CdS/CdTe solar wafers. An inline plant was to be constructed by ANTEC GmbH and ISFH. Film layers were to be optimised, and investigations were to show whether processing of single films is possible without breaking the vacuum, e.g. for etching. The results were to be used directly by ANTEC GmbH. An efficiency of 14 percent and an idle voltage of about 850 V were to be achieved with a film thickness of 2 {mu}m. To achieve these goals, the following project stages were envisaged: 1. Replacement of the expensive window material ITO by a less costly material. 2. Higher stability of the back contact by using appropriate intermediate layers. 3. Alternative activation processes other than the conventional CdCl{sub 2} activation. 4. Investigation of the effects of the activation step on the electric properties of the sample. [German] Die uebergreifende Aufgabenstellung des Projektes war die Entwicklung und Optimierung des Close-spaced-Sublimation verfahrens in einer Inline-Beschichtungsanlage fuer die Herstellung stabiler und hocheffizienter CdS/CdTe Duennschichtsolarzellen. Mit dem Wissen der ANTEC GmbH sollte zusammen mit dem ISFH eine Inline-Anlage konzipiert und gebaut werden. Die fuer die Solarzelle notwendigen Einzelschichten sollten in dem Inline-Prozess optimiert werden. Es sollte ermittelt werden, ob eine Prozessierung der Einzelschichten ohne Brechen des Vakuums, z.B. fuer einen Aetzschritt, moeglich ist. Die erzielten Ergebnisse sollen direkt der ANTEC GmbH zufliessen. In dem Projekt wurde als Endziel ein Wirkungsgrad der CdTe/CdS-Duennschichtsolarzelle von 14% und eine Erhoehung der Leerlaufspannung auf Werte um 850 mV angestrebt. Gleichzeitig sollte die CdTe-Schichtdicke auf 2 {mu}m vermindert werden. Um dieses Gesamtziel zu erreichen, sollen folgende Teilaufgaben bearbeitet werden: 1) Das teuere

  3. Nanowire CdS-CdTe Solar Cells with Molybdenum Oxide as Contact

    Science.gov (United States)

    Dang, Hongmei; Singh, Vijay P.

    2015-10-01

    Using a 10 nm thick molybdenum oxide (MoO3-x) layer as a transparent and low barrier contact to p-CdTe, we demonstrate nanowire CdS-CdTe solar cells with a power conversion efficiency of 11% under front side illumination. Annealing the as-deposited MoO3 film in N2 resulted in a reduction of the cell’s series resistance, from 9.97 Ω/cm2 to 7.69 Ω/cm2, and increase in efficiency from 9.9% to 11%. Under illumination from the back, the MoO3-x/Au side, the nanowire solar cells yielded Jsc of 21 mA/cm2 and efficiency of 8.67%. Our results demonstrate use of a thin layer transition metal oxide as a potential way for a transparent back contact to nanowire CdS-CdTe solar cells. This work has implications toward enabling a novel superstrate structure nanowire CdS-CdTe solar cell on Al foil substrate by a low cost roll-to roll fabrication process.

  4. Phosphorus Doping of Polycrystalline CdTe by Diffusion

    Energy Technology Data Exchange (ETDEWEB)

    Colegrove, Eric; Albin, David S.; Guthrey, Harvey; Harvey, Steve; Burst, James; Moutinho, Helio; Farrell, Stuart; Al-Jassim, Mowafak; Metzger, Wyatt K.

    2015-06-14

    Phosphorus diffusion in single crystal and polycrystalline CdTe material is explored using various methods. Dynamic secondary ion mass spectroscopy (SIMS) is used to determine 1D P diffusion profiles. A 2D diffusion model is used to determine the expected cross-sectional distribution of P in CdTe after diffusion anneals. Time of flight SIMS and cross-sectional cathodoluminescence corroborates expected P distributions. Devices fabricated with diffused P exhibit hole concentrations up to low 1015 cm-3, however a subsequent activation anneal enabled hole concentrations greater than 1016 cm-3. CdCl2 treatments and Cu based contacts were also explored in conjunction with the P doping process.

  5. Reflectance anisotropy spectra of CdTe(001) surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Vazquez-Nava, R.A.; Arzate, N.; Mendoza, B.S. [Photonics Division, Centro de Investigaciones en Optica A. C., Leon, Guanajuato (Mexico)

    2010-08-15

    We present first-principles calculations of reflectance anisotropy spectra (RAS) of the more common CdTe(001) surface reconstructions: Te-terminated (2 x 1) and Cd-terminated (2 x 1) and c(2 x 2). The last two reconstructions with a Cd coverage of half atomic layers. Calculations have been performed by using the density-functional formalism within the local-density approximation + scissors corrections. The electron-ion interaction has been modeled by ab initio, relativistic norm-conserving pseudopotentials. We have also calculated RAS spectra using a semi-empirical tight binding method (SETB) within a sp{sup 3} s{sup *} basis. We show RAS of each surface reconstruction and compare our theoretical results with experimental results reported in the literature and we found a good agreement between experimental and theoretical spectra for the (2 x 1) reconstructions. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

  6. Nanosized Thin SnO2 Layers Doped with Te and TeO2 as Room Temperature Humidity Sensors

    Directory of Open Access Journals (Sweden)

    Biliana Georgieva

    2014-05-01

    Full Text Available In this paper the humidity sensing properties of layers prepared by a new method for obtaining doped tin oxide are studied. Different techniques—SEM, EDS in SEM, TEM, SAED, AES and electrical measurements—are used for detailed characterization of the thin layers. The as-deposited layers are amorphous with great specific area and low density. They are built up of a fine grained matrix, consisting of Sn- and Te-oxides, and a nanosized dispersed phase of Te, Sn and/or SnTe. The chemical composition of both the matrix and the nanosized particles depends on the ratio RSn/Te and the evaporation conditions. It is shown that as-deposited layers with RSn/Te ranging from 0.4 to 0.9 exhibit excellent characteristics as humidity sensors operating at room temperature—very high sensitivity, good selectivity, fast response and short recovery period. Ageing tests have shown that the layers possess good long-term stability. Results obtained regarding the type of the water adsorption on the layers’ surface help better understand the relation between preparation conditions, structure, composition and humidity sensing properties.

  7. Growth, properties and applications of HgCdTe

    Science.gov (United States)

    Schmit, J. L.

    1983-12-01

    This paper provides primarily a review of the methods used to grow HgCdTe with a summary of some of its basic properties and applications. Methods of crystal growth fall generally into three classes: growth from the melt, from solution and from the vapor phase. All three methods have been and are being used to grow HgCdTe. The high vapor pressure of HgCdTe at the melting point, combined with a large segregation coefficient, have effectively limited the use of Czochralski or zone melting techniques, but two melt growth techniques have survived: (1) a variation of Bridgman growth called quench-anneal wherein a dendritic crystal is formed by quenching the melt and is homogenized by solid state recrystallization below the melting point, (2) a variation of freezing from a large volume called slush-growth wherein a melt is held in a temperature gradient for several weeks while a crystal grows. Growth from solution has taken the form of liquid phase epitaxy (LPE) on CdTe with the LPE systems including growth from Hg-rich, HgTe-rich and Te-rich solutions and using tipping, vertical dipping, vertical sliding and horizontal sliding. Vapor phase growth is very promising but is not yet in production. Techniques include growth by isothermal close spaced epitaxy in which HgTe is transported isothermally by chemical potential onto CdTe, molecular beam epitaxy (MBE) in which elements are evaporated in a high vacuum, and metal organic chemical vapor deposition (MOCVD) in which some of the metal atoms are carried to the substrate bound to organic radicals before being freed by pyrolysis. In all these methods, control of Hg pressure is a major concern. The fundamental properties discussed briefly are those of prime interest to detector manufacturers: energy gap ( Eg), intrinsic carrier concentration ( ni), and electrical activity of dopants. A reasonable fit to the Eg data from ˜ 20 papers is given by Eg = -0.302+1.93x+5.35×10 -4T(1-2x)-0.810x 2+0.832x 3. This gap, combined with k

  8. Synthesis of PbTe-SnTe particles by thermal decomposition of salts to create nano-structured thermoelectric materials

    Energy Technology Data Exchange (ETDEWEB)

    Leontyev, V.G.; Ivanova, L.D. [Institution of Russian Academy of Sciences A.A. Baikov Institute of Metallurgy and Material Science RAS, Leninskii prospect, 49, 119991 Moscow (Russian Federation); Bente, K. [Institut fuer Mineralogie, Kristallographie und Materialwissenschaft, Leipzig University, Scharnhorststr. 20, 04275 Leipzig (Germany); Gremenok, V.F. [State Scientific and Production Association ' ' Scientific-Practical Materials Research Centre of the National Academy of Sciences of Belarus' ' , P. Brovka str. 19, 220072 Minsk (Belarus)

    2012-05-15

    Micro- and nanocrystalline particles of Pb-Sn-Te mixed crystals were synthesized using thermal decomposition and chemical interaction of lead acetate, tin oxalate and tellurium powder mixture in H{sub 2} atmosphere. For the process parameter optimization data of thermal gravimetry (TG), X-ray diffraction (XRD), electronic microscopy (TEM, SEM) and measurements of the specific surface of particles were used. Additionally the influence of gas phases on the decomposition kinetics, crystal structure, size, specific surface of the particles, gains composition and the physical properties were analyzed. Seebeck coefficient values increased and conductivity decreased with decreasing tin concentration. The presented method for preparing PbTe-SnTe polydisperse particles is developed to create nano-structured thermoelectric materials with high figure of merit. (copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  9. Comparison of CdTe and CdZnTe Detectors for Field Determination of Uranium Isotopic Enrichments

    Energy Technology Data Exchange (ETDEWEB)

    Hofstetter, KJ

    2004-01-23

    A performance comparison of a CdTe and a CdZnTe detector when exposed to uranium samples of various isotopic enrichments has been performed. These high-resolution detectors can assist in the rapid determination of uranium isotopic content of illicit material. Spectra were recorded from these room temperature semiconductor detectors with a portable multi-channel analyzer, both in the laboratory and in a field environment. Both detectors were operated below ambient temperature using the vendor supplied thermoelectric coolers. Both detectors had nominally the same active volume (18 mm3 for the CdZnTe and 25 mm3 for the CdTe detector) and resolution. Spectra of samples of known isotopic content were recorded at fixed geometries. An evaluation of potential signature g rays for the detection of enriched uranium was completed. Operational advantages and disadvantages of each detector are discussed. There is a need to improve the detection sensitivity during the interdiction of special nuclear materials (SNM) for increased homeland protection. It is essential to provide additional tools to first responders and law enforcement personnel for assessing nuclear and radiological threats.

  10. Feasibility of Open Tube Slider Growth of HgCdTe from Te-Rich Solution.

    Science.gov (United States)

    1980-02-01

    od of Equation (26), which assumes CdTe and HgTe molecules are dissolved in Te and that the solution is 3.2 percent less dense than the solid...finished slice is protected with a layer of beeswax and diced to the size of our slider system, either I 1Xlcm 2 or 2X3cm2 . Just before use, the...h time allowed for the solute to dissolve at 770’C produces ent with the annealing studies of Schrnt and Stelzer 1211 on 55 ’- IKIKE TRANSACTIONS ON

  11. COMPARISON OF CHARACTERIZATION TECHNIQUES IN P-ON-N HgCdTe LWIR PHOTODIODES TECHNOLOGY

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    In this paper standard techniques for characterization of HgCdTe liquid phase epitaxial layers (LPE) were presented. The performance of long wavelength p-on-n HgCdTe photodiodes fabricated by arsenic diffusion was described. The correlation between LPE HgCdTe material parameters and properties of the infrared photodiodes was demonstrated.

  12. Comparative study of SnS recrystallization in molten CdI{sub 2}, SnCl{sub 2}and KI

    Energy Technology Data Exchange (ETDEWEB)

    Timmo, Kristi; Kauk-Kuusik, Marit; Pilvet, Maris; Mikli, Valdek; Kaerber, Erki; Raadik, Taavi; Leinemann, Inga; Altosaar, Mare; Raudoja, Jaan [Department of Materials Science, Tallinn University of Technology, Tallinn (Estonia)

    2016-01-15

    In the present study, the recrystallization of polycrystalline SnS in different molten salts CdI{sub 2}, SnCl{sub 2} and KI as flux materials are presented. The recrystallization and growth of polycrystalline material in molten salts produces unique SnS monograin powders usable in monograin layer solar cells. XRD and Raman analysis revealed that single phase SnS powder can be obtained in KI at 740 C and in SnCl{sub 2} at 500 C. Long time heating of SnS in molten CdI{sub 2} was accompanied by chemical interaction between SnS and CdI{sub 2} that resulted in a mixture of CdS and Sn{sub 2}S{sub 3} crystals. SEM images showed that morphology of crystals can be controlled by the nature of the flux materials: needle-like Sn{sub 2}S{sub 3} together with round edged crystals of CdS in CdI{sub 2}, flat crystals of SnS with smooth surfaces in SnCl{sub 2} and well-formed SnS crystals with rounded edges in KI had been formed. The temperatures of phase transitions and/or the interactions of SnS and flux materials were determined by differential thermal analysis. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  13. Superconducting thin films of (100) and (111) oriented indium doped topological crystalline insulator SnTe

    Energy Technology Data Exchange (ETDEWEB)

    Si, Weidong, E-mail: wds@bnl.gov, E-mail: qiangli@bnl.gov; Zhang, Cheng; Wu, Lijun; Ozaki, Toshinori; Gu, Genda; Li, Qiang, E-mail: wds@bnl.gov, E-mail: qiangli@bnl.gov [Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973 (United States)

    2015-08-31

    Recent discovery of the topological crystalline insulator SnTe has triggered a search for topological superconductors, which have potential application to topological quantum computing. The present work reports on the superconducting properties of indium doped SnTe thin films. The (100) and (111) oriented thin films were epitaxially grown by pulsed-laser deposition on (100) and (111) BaF{sub 2} crystalline substrates, respectively. The onset superconducting transition temperatures are about 3.8 K for (100) and 3.6 K for (111) orientations, slightly lower than that of the bulk. Magneto-resistive measurements indicate that these thin films may have upper critical fields higher than that of the bulk. With large surface-to-bulk ratio, superconducting indium doped SnTe thin films provide a rich platform for the study of topological superconductivity and potential device applications based on topological superconductors.

  14. Emitter/absorber interface of CdTe solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Song, Tao [Physics Department, Colorado State University, Fort Collins, Colorado 80523, USA; Kanevce, Ana [National Renewable Energy Laboratory, Golden, Colorado 80401, USA; Sites, James R. [Physics Department, Colorado State University, Fort Collins, Colorado 80523, USA

    2016-06-17

    The performance of CdTe solar cells can be very sensitive to their emitter/absorber interfaces, especially for high-efficiency cells with improved bulk properties. When interface defect states are located at efficient recombination energies, performance losses from acceptor-type interface defects can be significant. Numerical simulations show that the emitter/absorber band alignment, the emitter doping and thickness, and the defect properties of the interface (i.e. defect density, defect type, and defect energy) can all play significant roles in the interface recombination. In particular, a type I heterojunction with small conduction-band offset (0.1 eV /= 0.4 eV), however, can impede electron transport and lead to a reduction of photocurrent and fill-factor. In contrast to the spike, a 'cliff' (.delta..EC < 0 eV) is likely to allow many holes in the vicinity of the interface, which will assist interface recombination and result in a reduced open-circuit voltage. In addition, a thin and highly-doped emitter can invert the absorber, form a large hole barrier, and decrease device performance losses due to high interface defect density. CdS is the most common emitter material used in CdTe solar cells, but the CdS/CdTe interface is in the cliff category and is not favorable from the band-offset perspective. Other n-type emitter choices, such as (Mg,Zn)O, Cd(S,O), or (Cd,Mg)Te, can be tuned by varying the elemental ratio for an optimal positive value of ..delta..EC. These materials are predicted

  15. Progress in the Development of CdTe and CdZnTe Semiconductor Radiation Detectors for Astrophysical and Medical Applications

    Directory of Open Access Journals (Sweden)

    Anna Maria Mancini

    2009-05-01

    Full Text Available Over the last decade, cadmium telluride (CdTe and cadmium zinc telluride (CdZnTe wide band gap semiconductors have attracted increasing interest as X-ray and gamma ray detectors. Among the traditional high performance spectrometers based on silicon (Si and germanium (Ge, CdTe and CdZnTe detectors show high detection efficiency and good room temperature performance and are well suited for the development of compact and reliable detection systems. In this paper, we review the current status of research in the development of CdTe and CdZnTe detectors by a comprehensive survey on the material properties, the device characteristics, the different techniques for improving the overall detector performance and some major applications. Astrophysical and medical applications are discussed, pointing out the ongoing Italian research activities on the development of these detectors.

  16. Progress in the Development of CdTe and CdZnTe Semiconductor Radiation Detectors for Astrophysical and Medical Applications.

    Science.gov (United States)

    Sordo, Stefano Del; Abbene, Leonardo; Caroli, Ezio; Mancini, Anna Maria; Zappettini, Andrea; Ubertini, Pietro

    2009-01-01

    Over the last decade, cadmium telluride (CdTe) and cadmium zinc telluride (CdZnTe) wide band gap semiconductors have attracted increasing interest as X-ray and gamma ray detectors. Among the traditional high performance spectrometers based on silicon (Si) and germanium (Ge), CdTe and CdZnTe detectors show high detection efficiency and good room temperature performance and are well suited for the development of compact and reliable detection systems. In this paper, we review the current status of research in the development of CdTe and CdZnTe detectors by a comprehensive survey on the material properties, the device characteristics, the different techniques for improving the overall detector performance and some major applications. Astrophysical and medical applications are discussed, pointing out the ongoing Italian research activities on the development of these detectors.

  17. A new model for the O{sub Te}-V{sub Cd} complex in CdTe

    Energy Technology Data Exchange (ETDEWEB)

    Bastin, Dirk; Lavrov, Edward; Weber, Joerg [Technische Univ. Dresden (Germany); Schneider, Juergen; Fauler, Alex; Fiederle, Michael [Freiburger Materialforschungszentrum, 79104 Freiburg im Breisgau (Germany)

    2012-07-01

    CdTe single crystals treated in CdSO{sub 4} vapor at 850 C are investigated by IR absorption. Two local vibrational modes (LVM) at 1096.8 (v{sub 1}) and 1108.4 cm{sup -1} (v{sub 2}) appear in the sample as the result of the thermal treatment. The modes were previously identified by Chen et al. as vibrations of the O{sub Te}-V{sub Cd} complex. We detect in our samples additional LVMs with intensities which match the natural abundance of the sulfur isotopes. The reported dependence of the absorption intensities of v{sub 1} and v{sub 2} from the oxygen concentration of the samples points to a model of an sulfur-oxygen complex of the vibrating center. From the intensities of the IR absorption involving the {sup 18}O isotope, we conclude that two oxygen atoms contribute to the LVMs.

  18. Synthesis of CdTe/SiO2 Composites and Their Fluorescence Properties

    Institute of Scientific and Technical Information of China (English)

    WANG Mei-ping; LIN Jin-hui; SHAN Chuan-sheng

    2011-01-01

    Thioglycolic acid(TGA)-stabilized CdTe nanocrystals(NCs) were prepared with sodium tellurite as tellurium source,which avoids the cumbersome processes associated with H2Te or NaHTe sources.Fluorescent CdTe/SiO2 composites were synthesized by a sol-gel method without the exchange of surface ligands.The phase structure of CdTe NCs was investigated by X-ray diffractometry.For comparison,some characterizations were done for both the CdTe NCs and the composites.CdTe NCs and CdTe/SiO2 composites were characterized with TEM,digital camera and fluorescence spectrophotometer.The stability of CdTe NCs and the composites were investigated in phosphate-buffered saline(PBS) buffer and the fluorescent properties of the composites were discussed in detail.

  19. Near-IR bandgap engineering employing the alloy (CdTe)x(In2Te3)1-x

    OpenAIRE

    M. Meléndez Lira; M. Zapata Torres; R. Castro Rodriguez

    2001-01-01

    Bandgap variation in the near infrared employing CdTe-based alloys has potential applications in the optoelectronic industry. Pursuing it we have deposited thin films of the alloy (CdTe)x(In2Te3)1-x employing the closed space vapor transport technique combined with free evaporation. As sources we employed CdTe and In2Te3 powders. The temperature of the sources and the substrate controlled sample composition. Structural characterization was carried out employing xray diffraction and scanning e...

  20. The influence of grain boundary diffusion on the electro-optical properties of CdTe/CdS solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Levi, D.H.; Albin, D.S.; Gessert, T.A.; Reedy, R.C.; Ahrenkiel, R.K. [National Renewable Energy Lab., Golden, CO (United States); Woods, L.M. [Colorado State Univ., Fort Collins, CO (United States)

    1998-09-01

    The authors report on a study of the effects of diffusion of metals through polycrystalline CdTe thin films. The metals Ni, Pd, Cu, Cr, and Te are deposited onto the back surface of 10-{micro}m thick CdTe/CdS device structures using room-temperature evaporation. The authors found that four out of the five metals produce significant changes in the photoluminescence (PL) of the near-junction CdTe material. These changes are explained in terms of spatial variations of the photoexcited carrier distribution and spatial variations in the sulfur composition of the CdTeS alloy material near the CdTeS interface. The changes in carrier distribution appear to be associated with band bending and electric fields induced by diffusion of the metals to the CdTe/CdS interface. In addition to PL measurements, the authors have also utilized a technique for detaching the CdTe film from the CdS/TCO/glass superstrate to directly access the front surface of the CdTe absorber layer. The authors have used secondary ion mass spectroscopy to measure the metal diffusion profiles from this interface.

  1. Solution-Processed, Ultrathin Solar Cells from CdCl3(-)-Capped CdTe Nanocrystals: The Multiple Roles of CdCl3(-) Ligands.

    Science.gov (United States)

    Zhang, Hao; Kurley, J Matthew; Russell, Jake C; Jang, Jaeyoung; Talapin, Dmitri V

    2016-06-22

    Solution-processed CdTe solar cells using CdTe nanocrystal (NC) ink may offer an economically viable route for large-scale manufacturing. Here we design a new CdCl3(-)-capped CdTe NC ink by taking advantage of novel surface chemistry. In this ink, CdCl3(-) ligands act as surface ligands, sintering promoters, and dopants. Our solution chemistry allows obtaining very thin continuous layers of high-quality CdTe which is challenging for traditional vapor transport methods. Using benign solvents, in air, and without additional CdCl2 treatment, we obtain a well-sintered CdTe absorber layer from the new ink and demonstrate thin-film solar cells with power conversion efficiency over 10%, a record efficiency for sub-400 nm thick CdTe absorber layer.

  2. Long Carrier Lifetimes in Large-Grain Polycrystalline CdTe Without CdCl2

    Energy Technology Data Exchange (ETDEWEB)

    Jensen, Soren A.; Burst, James M.; Duenow, Joel N.; Guthrey, Harvey L.; Moseley, John; Moutinho, Helio R.; Johnston, Steve W.; Kanevce, Ana; Al-Jassim, Mowafak M.; Metzger, Wyatt K.

    2016-06-27

    For decades, polycrystalline CdTe thin films for solar applications have been restricted to grain sizes of microns or less whereas other semiconductors such as silicon and perovskites have produced devices with grains ranging from less than a micron to more than 1 mm. Because the lifetimes in as-deposited polycrystalline CdTe films are typically limited to less than a few hundred picoseconds, a CdCl2 treatment is generally used to improve the lifetime; but this treatment may limit the achievable hole density by compensation. Here, we establish methods to produce CdTe films with grain sizes ranging from hundreds of nanometers to several hundred microns by close-spaced sublimation at industrial manufacturing growth rates. Two-photon excitation photoluminescence spectroscopy shows a positive correlation of lifetime with grain size. Large-grain, as-deposited CdTe exhibits lifetimes exceeding 10 ns without Cl, S, O, or Cu. This uncompensated material allows dopants such as P to achieve a hole density of 1016 cm-3, which is an order of magnitude higher than standard CdCl2-treated devices, without compromising the lifetime.

  3. Long carrier lifetimes in large-grain polycrystalline CdTe without CdCl2

    Science.gov (United States)

    Jensen, S. A.; Burst, J. M.; Duenow, J. N.; Guthrey, H. L.; Moseley, J.; Moutinho, H. R.; Johnston, S. W.; Kanevce, A.; Al-Jassim, M. M.; Metzger, W. K.

    2016-06-01

    For decades, polycrystalline CdTe thin films for solar applications have been restricted to grain sizes of microns or less whereas other semiconductors such as silicon and perovskites have produced devices with grains ranging from less than a micron to more than 1 mm. Because the lifetimes in as-deposited polycrystalline CdTe films are typically limited to less than a few hundred picoseconds, a CdCl2 treatment is generally used to improve the lifetime; but this treatment may limit the achievable hole density by compensation. Here, we establish methods to produce CdTe films with grain sizes ranging from hundreds of nanometers to several hundred microns by close-spaced sublimation at industrial manufacturing growth rates. Two-photon excitation photoluminescence spectroscopy shows a positive correlation of lifetime with grain size. Large-grain, as-deposited CdTe exhibits lifetimes exceeding 10 ns without Cl, S, O, or Cu. This uncompensated material allows dopants such as P to achieve a hole density of 1016 cm-3, which is an order of magnitude higher than standard CdCl2-treated devices, without compromising the lifetime.

  4. In-situ CdS/CdTe Heterojuntions Deposited by Pulsed Laser Deposition

    KAUST Repository

    Avila-Avendano, Jesus

    2016-04-09

    In this paper pulsed laser deposition (PLD) methods are used to study p-n CdTe/CdS heterojunctions fabricated in-situ. In-situ film deposition allows higher quality p-n interfaces by minimizing spurious contamination from the atmosphere. Morphologic and structural analyses were carried for CdTe films deposited on various substrates and different deposition conditions. The electrical characteristics and performance of the resulting p-n heterojunctions were studied as function of substrate and post-deposition anneal temperature. In-situ growth results on diodes with a rectification factor of ~ 105, an ideality factor < 2, and a reverse saturation current ~ 10-8 A. The carrier concentration in the CdTe film was in the range of ~ 1015 cm-3, as measured by C-V methods. The possible impact of sulfur diffusion from the CdS into the CdTe film is also investigated using High Resolution Rutherford Back-Scattering.

  5. Manufacturing of CSS CdTe solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Bonnet, D. [ANTEC Solar GmbH, Rudisleben (Germany)

    2000-02-21

    Due to its basic physical and chemical properties CdTe has become a favoured base material for thin film solar cells, using robust, high-throughput manufacturing procedures. The technology shows significant potential for attaining cost levels of <0.5 Euro/W{sub p}. Close-spaced sublimation (CSS) is the fastest and simplest deposition process for both semiconductors used, CdTe and CdS, permitting in-line production at a high linear speed of about 1 m/min. The individual manufacturing steps for integrated modules are explained in view of their incorporation into the production line. ANTEC solar GmbH is engaged to enter the production of CdTe thin film modules on a scale of 10 MW{sub p} (100000 m{sup 2}) per annum, using CSS as the deposition procedure for the semiconductor films, and high-rate in-line sputtering for transparent and opaque contacts. Standard module size will be 60 x 120 cm{sup 2}. The production line is presently under construction. (orig.)

  6. Effects of the Au/CdTe back contact on IV and CV characteristics of Au/CdTe/CdS/TCO solar cells

    Science.gov (United States)

    Niemegeers, Alex; Burgelman, Marc

    1997-03-01

    A simple analytical theory is presented to explain the measured roll over and cross over behaviour of the IV characteristics of thin film CdTe solar cells. It involves a classical description of the CdS/CdTe junction and the CdTe/back contact structure and is extended with a new description of minority carrier current in the CdTe contact region. This extension is crucial in describing the light dependence of the forward IV curves, and hence cross over. The same model also explains the measured CV curves. It is shown that analysis of the capacitance measurement can yield additional information about the doping density of CdTe in the vicinity of the contact. A relationship between the fill factor of the solar cell and the barrier height of the back contact is derived; this relation is useful as a new, practical criterion for the quality of the back contact. The results of this simple analytical model are confirmed by full numerical calculations of the dc and ac characteristics.

  7. Grenzflächenmodifikation des CdS/ CdTe Heterokontaktes für CdTe Dünnschichtsolarzellen

    OpenAIRE

    Feldmeier, Eduard

    2015-01-01

    In der vorliegenden Dissertation werden verschiedene Depositionsmethoden der Cadmiumsulfid (CdS)-Fensterschicht von Cadmiumtellurid (CdTe)-Dünnschichtsolarzellen miteinander verglichen. Als alternative, vakuumbasierte Abscheidemethoden werden kathodenzerstäubte sowie thermisch verdampfte CdS-Schichten im Vergleich zu der am Fachgebiet verwendeten Standardabscheidemethode „Closed Space Sublimation“ (CSS) gegenübergestellt. Die auf einem kommerziellen Glassubstrat, mit fluor-dotiertem Zinnoxid ...

  8. Dark-red-emitting CdTe/Cd1-x Znx S core/shell quantum dots: preparation and properties.

    Science.gov (United States)

    Yang, Ping; Murase, Norio

    2013-01-01

    CdTe nanocrystals (NCs) were fabricated through an organic synthesis. The growth and properties of CdTe NCs depended strongly on the preparation conditions. In a reaction system of octadecene and tetradecylphosphonic acid (TDPA), the growth was slow. CdTe NCs with cubic-like morphology were created in trioctylamine (TOA) using octadecylphosphonic acid (ODPA)-CdO or TDPA-CdO as precursors. The TOA and ODPA system gives rise to NCs with high photoluminescence (PL) efficiencies (12%). A Cdx Zn1-x S shell coating on the CdTe core, gave rise to tunable dark red PL (630-670 nm). The morphology and PL properties of the CdTe cores were drastically affected by shell coating and this determined the properties of CdTe/Cdx Zn1-x S NCs. Small CdTe NCs were easily coated with Cdx Zn1-x S shells. The resulting core/shell NCs revealed a spherical morphology. However, shell growth became slow when large CdTe cores were used. This is ascribed to the cores with a cubic-like morphology. CdS interlayer plays an important role for the formation of the CdTe/Cdx Zn1-x S NCs because the experimental result indicated it is difficult to coat CdTe NCs with a ZnS shell. The core/shell NCs benefited from a Cdx Zn1-x S composite shell because CdTe/CdS NCs created via a similar procedure revealed a low PL efficiency.

  9. Growth experiment of narrow band-gap semiconductor PbSnTe single crystals in space (M-1)

    Science.gov (United States)

    Yamada, Tomoaki

    1993-01-01

    An experiment on crystal growth of Pb(1-x)Sn(x)Te in microgravity is planned. This material is an alloy of the compound semiconductors PbTe and SnTe. It is a promising material for infrared diode lasers and detectors in the wavelength region between 6 and 30 micron. Since the electrical properties of Pb(1-x)Sn(x)Te depend greatly on the Pb/Sn ratio and crystalline defects as well as impurity concentration, homogeneous, defect-free, high-quality crystals are anticipated. Although many growth methods, such as the pulling method, the Bridgman method, the vapor growth method, etc., have been applied to the growth of Pb(1-x)Sn(x)Te, large, homogeneous, low-defect-density crystals have not yet been grown on Earth. The unsuccessful results were caused by buoyancy-driven convection in the fluids induced by the specific gravity difference between heated and cooled fluids on Earth. A crystal is grown by cooling the melt from one end of the ampoule. In crystal growth from the melt, about 30 percent of the SnTe in the melt is rejected at the solid-liquid interface during solidification. On Earth, the rejected SnTe is completely mixed with the remaining melt by convection in the melt. Therefore, SnTe concentration in the melt, and accordingly in the crystal, increases as the crystal grows. In the microgravity environment, buoyancy-driven convection is suppressed because the specific gravity difference is negligible. In that case, the rejected SnTe remains at the solid-liquid interface and its concentration increases only at the interface. If the growth rate is higher than the PbTe-SnTe interdiffusion rate, the amount of SnTe which diffuses from the interface into the melt increases as SnTe piles up at the interface, and finally it balances the amount of rejected SnTe during solidification, resulting in steady-state SnTe transportation at the interface. By using this principle, compositionally homogeneous crystals can be grown. Furthermore, low-defect-density crystals will be

  10. Surface treatment of the window layer in CdS/CdTe solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Cho, Shin Haeng; Kim, Sang Su; Park, Min Hyuk; Suh, Jong Hee; Hong, Jin Ki [Korea University, Jochiwon (Korea, Republic of)

    2014-11-15

    CdS films are used as window layers in CdS/CdTe solar cells, and an annealing process is required to promote grain growth and recrystallization in them. However, when annealing is performed in an air atmosphere, oxides such as CdO and CdSO{sub 4} form on parts of the layer's surface, which reduces the shunt resistance and the fill factor and results in poor device performance. In this study, we annealed the CdS film in a CdCl{sub 2} atmosphere instead of air. Then, CdCl{sub 2} annealing and air annealing were compared by investigating the structural and the electrical properties of the CdS window layers. Our results reveal that the CdCl{sub 2} annealing protects the CdS film from oxidation and provides good recrystallization conditions. We also found that this CdCl{sub 2} annealing enhance the device's performance. In particular, considerably higher shunt resistance and conversion efficiency were obtained for the CdCl{sub 2}-annealed device compared with the air-annealed device.

  11. Comparative study of CdTe sources used for deposition of CdTe thin films by close spaced sublimation technique

    OpenAIRE

    Pinheiro,Wagner Anacleto; Falcão, Vivienne Denise; Cruz,Leila Rosa de Oliveira; Ferreira,Carlos Luiz

    2006-01-01

    Unlike other thin film deposition techniques, close spaced sublimation (CSS) requires a short source-substrate distance. The kind of source used in this technique strongly affects the control of the deposition parameters, especially the deposition rate. When depositing CdTe thin films by CSS, the most common CdTe sources are: single-crystal or polycrystalline wafers, powders, pellets or pieces, a thick CdTe film deposited onto glass or molybdenum substrate (CdTe source-plate) and a sintered C...

  12. Improved photovoltaic performance of heterostructured tetrapod-shaped CdSe/CdTe nanocrystals using C60 interlayer

    Energy Technology Data Exchange (ETDEWEB)

    Li, Yanqin; Mastria, Rosanna; Fiore, Angela; Nobile, Concetta; Yin, Lunxiang; Cheng, Gang; Cingolani, Roberto; Manna, Liberato; Gigli, Giuseppe [National Nanotechnology Lab of CNR-INFM (NNL), University of Salento, Lecce (Italy); Biasiucci, Mariano [National Nanotechnology Lab of CNR-INFM (NNL), University of Salento, Lecce (Italy); Physical Department, University of Salerno, Baronissi (Italy); Cucolo, Anna Maria [Physical Department, University of Salerno, Baronissi (Italy)

    2009-11-26

    Photovoltaic (PV) devices based on CdSe/CdTe-C60 active layers, in which the nanocrystal and fullerene (C60) layers work as electron-donor and electron-acceptor/transport layers, respectively, were fabricated. Efficiencies up to 0.62% were reached in the hybrid cells. The PV performance was greatly improved with respect to that of CdSe/CdTe-P3HT- and CdSe/CdTe-based devices, fabricated as reference. (Abstract Copyright [2009], Wiley Periodicals, Inc.)

  13. Low-Cost Lattice Matching Si Based Composite Substrates for HgCdTe

    Science.gov (United States)

    2013-09-01

    211). ..............................................5 Figure 3. Relationship between calculated alloy compositions based on Se/CdTe BEP ratio and...Se:CdTe beam equivalent pressure ( BEP ) ratios. During CdSeTe growth, Se and Te are in competition for the same nucleation sites. If we assume that all...therefore, x(cal) = ΦSe/ΦCd = 2ΦSe/ΦCdTe, where Φ is the BEP of the material, measured by the nude ion gauge at the substrate position. Figure 3 shows the

  14. Dynamics of photoexcited carrier relaxation and recombination in CdTe/CdS thin films

    Energy Technology Data Exchange (ETDEWEB)

    Levi, D.H.; Fluegel, B.D.; Ahrenkiel, R.K. [National Renewable Energy Lab., Golden, CO (United States)] [and others

    1996-05-01

    Efficiency-limiting defects in photovoltaic devices are readily probed by time-resolved spectroscopy. This paper presents the first direct optical measurements of the relaxation and recombination pathways of photoexcited carriers in the CdS window layer of CdTe/CdS polycrystalline thin films. Femtosecond time-resolved pump/probe measurements indicate the possible existence of a two-phase CdS/CdSTe layer, rather than a continuously graded alloy layer at the CdTe/CdS interface. Complementary time-resolved photoluminescence (PL) measurements show that the photoexcited carriers are rapidly captured by deep-level defects. The temporal and density-dependent properties of the photoluminescence prove that the large Stokes shift of the PL relative to the band edge is due to strong phonon coupling to deep-level defects in CdS. The authors suggest that modifications in the CdS processing may enhance carrier collection efficiency in the blue spectral region.

  15. Variable Temperature Current-Voltage Measurements of CdTe Solar Cells

    Science.gov (United States)

    Smith, A. D.

    2000-03-01

    We have used a 2" x 2" Peltier heat pump chip powered with 24 V from a computer power supply to build a variable temperature stage for current voltage measurements of solar cells. A voltage divider was used to achieve several different set point temperatures from 25 oC to -24 oC. This system was used with a halogen lamp to study the electrical performance of polycrystalline thin-film solar cells fabricated in our group. These cells have the superstrate structure glass/SnO2:F/CdS/CdTe/metal.(1) The I-V characteristic shows evidence of a blocking back-diode which sets in below room temperature. This behavior will be related to the diffusion into the CdTe of the metals used for our back contact.(2) 1. M. Shao, A. Fischer, D. Grecu, U. Jayamaha, E. Bykov, G. Contreras-Puente, R.G. Bohn, and A.D. Compaan, Appl. Phys. Lett. 69, 3045-3047 (1996). 2. D. Grecu and A.D. Compaan, Appl. Phys. Lett. 75, 361-363 (1999).

  16. Dependence of CdTe response of bias history

    Energy Technology Data Exchange (ETDEWEB)

    Sites, J.R.; Sasala, R.A.; Eisgruber, I.L. [Colorado State Univ., Boulder, CO (United States)

    1995-11-01

    Several time-dependent effect have been observed in CdTe cells and modules in recent years. Some appear to be related to degradation at the back contact, some to changes in temperature at the thin-film junction, and some to the bias history of the cell or module. Back-contact difficulties only occur in some cases, and the other two effects are reversible. Nevertheless, confusion in data interpretation can arise when these effects are not characterized. This confusion can be particularly acute when more than one time-dependent effect occurs during the same measurement cycle. The purpose of this presentation is to help categorize time-dependent effects in CdTe and other thin-film cells to elucidate those related to bias history, and to note differences between cell and module analysis.

  17. Digital pulse-shape processing for CdTe detectors

    CERN Document Server

    Bargholtz, C; Maartensson, L; Wachtmeister, S

    2001-01-01

    CdTe detectors suffer from low photo-peak efficiency and poor energy resolution. These problems are due to the drift properties of charge carriers in CdTe where particularly the holes have small mobility and trapping time. This is reflected in the amplitude and the shape of the detector output. To improve this situation a digital method is introduced where a sampling ADC is used to make a detailed measurement of the time evolution of the pulse. The measured pulse shape is fitted with a model. For the detector under study a model taking hole trapping into account significantly improves the photo-peak efficiency. The description of the hole component is, however, not fully satisfactory since for pulses with a large hole contribution a broadening of the full-energy peak occurs. Allowing for inhomogeneities in the detector material within the model partially remedies this deficiency.

  18. Point Defect Characterization in CdZnTe

    Energy Technology Data Exchange (ETDEWEB)

    Gul,R.; Li, Z.; Bolotnikov, A.; Keeter, K.; Rodriguez, R.; James, R.

    2009-03-24

    Measurements of the defect levels and performance testing of CdZnTe detectors were performed by means of Current Deep Level Transient Spectroscopy (I-DLTS), Transient Charge Technique (TCT), Current versus Voltage measurements (I-V), and gamma-ray spectroscopy. CdZnTe crystals were acquired from different commercial vendors and characterized for their point defects. I-DLTS studies included measurements of defect parameters such as energy levels in the band gap, carrier capture cross sections, and defect densities. The induced current due to laser-generated carriers was measured using TCT. The data were used to determine the transport properties of the detectors under study. A good correlation was found between the point defects in the detectors and their performance.

  19. Optical properties of CdTe: Experiment and modeling

    Science.gov (United States)

    Adachi, Sadao; Kimura, Toshifumi; Suzuki, Norihiro

    1993-09-01

    The real epsilon(sub 1) and imaginary epsilon(sub 2) portions of the dielectric function of CdTe were measured by spectroscopic ellipsometry (SE) in the 1.1-5.6 eV photon-energy range at room temperature. The data obtained were analyzed using different theoretical models, namely the harmonic-oscillator approximation, the standard critical point, and the model dielectric function. These models include the E(sub 0), E(sub 0) + Delta(sub 0), E(sub 1), E(sub 1) + Delta(sub 1), and E(sub 2) gaps as the main dispersion mechanisms. The consequences were reported and of particular interest was the difference in the analyzed results between these theoretical models. Dielectric-related optical constants of CdTe, such as the complex refractive index, the absorption coefficient, and normal-incidence reflectivity, were also investigated.

  20. Spectral response of CdS/CdTe solar cells obtained with different S/Cd ratios for the CdS chemical bath

    Energy Technology Data Exchange (ETDEWEB)

    Vigil-Galan, O.; Sastre-Hernandez, J.; Contreras-Puente, G.; Tufino-Velazquez, M. [Escuela Superior de Fisica y Matematicas, Instituto Politecnico Nacional, 07738 Mexico D. F. (Mexico); Arias-Carbajal, A. [Facultad de Quimica, IMRE, Universidad de La Habana, 10400 La Habana (Cuba); Mendoza-Perez, R. [Universidad Autonoma de la Ciudad de Mexico, 09970 Mexico, D. F. (Mexico); Santana, G. [Instituto de Investigacion en Materiales, UNAM, 04510 Mexico, D. F. (Mexico); Morales-Acevedo, A. [Departamento de Ingenieria Electrica, CINVESTAV-IPN, 07360 Mexico, D. F. (Mexico)

    2006-09-22

    In this work, the influence of the variation of chemical bath thiourea concentration in the solution for depositing CdS layers upon the spectral response of chemical bath deposition (CBD)-CdS/CdTe solar cells is studied. Although changes in the short and long wavelength range for the spectral response of the cells were observed in dependence of the thiourea concentration, no significant changes were observed in the diffusion length of minority carriers in the CdTe layer, as determined from the constant photocurrent method, when the thiourea concentration is increased in the CdS deposition solution. (author)

  1. Rapid synthesis of aqueous CdTe/CdSe core-shell quantum dots with highly photostability using microwave irradiation%微波辅助快速合成水溶性CdTe/CdSe核壳量子点

    Institute of Scientific and Technical Information of China (English)

    徐昕; 贺蓉; 崔大祥

    2011-01-01

    以巯基乙酸(TGA)作为稳定剂,用微波辅助法快速合成了水溶性CdTe/CdSe核壳量子点.比较了传统水热法和微波辅助法制备的量子点性能,研究了加热温度、反应物配比及CdTe量子点浓度对CdTe/CdSe核壳量子点的性能影响.研究结果表明,核壳结构的CdTe/CdSe量子点比单一的CdTe量子点具有更优异的光致发光强度和光稳定性.%In this paper, present a new procedure for the rapid synthesis of luminescent CdTe/CdSe core-shell quantum dots (QDs) in water phase by microwave irradiation method. The influences of microwave irradiation and a series of experimental variables, including heating temperature, molar ratios and concentration of precursors on the synthesis of QDs were investigated systematically. The results of high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) showed that the as-prepared nanocrystals had high crystallinity. In comparison with the plain CdTe QDs, both the photoluminescence quantum yield (PLQY) and photostability against UV irradiation of the CdTe/CdSe core-shell QDs have been greatly improved.

  2. First-principles study of roles of Cu and Cl in polycrystalline CdTe

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Ji-Hui; Park, Ji-Sang; Metzger, Wyatt [National Renewable Energy Laboratory, Golden, Colorado 80401 (United States); Yin, Wan-Jian [National Renewable Energy Laboratory, Golden, Colorado 80401 (United States); College of Physics, Optoelectronics and Energy and Collaborative, Innovation Center of Suzhou Nano Science and Technology, Soochow University, Suzhou 215006 (China); Wei, Su-Huai, E-mail: suhuaiwei@csrc.ac.cn [National Renewable Energy Laboratory, Golden, Colorado 80401 (United States); Beijing Computational Science Research Center, Beijing 100094 (China)

    2016-01-28

    Cu and Cl treatments are important processes to achieve high efficiency polycrystalline cadmium telluride (CdTe) solar cells, thus it will be beneficial to understand the roles they play in both bulk CdTe and CdTe grain boundaries (GBs). Using first-principles calculations, we systematically study Cu and Cl-related defects in bulk CdTe. We find that Cl has only a limited effect on improving p-type doping and too much Cl can induce deep traps in bulk CdTe, whereas Cu can enhance p-type doping of bulk CdTe. In the presence of GBs, we find that, in general, Cl and Cu will prefer to stay at GBs, especially for those with Te-Te wrong bonds, in agreement with experimental observations.

  3. Effect of ZnTe/ZnTe:Cu complex back-contact on device characteristics of CdTe solar cells

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    ZnTe/ZnTe:Cu complex layers deposited by vacuum co-evaporation have been in- troduced to CdS/CdTe solar cells. The C-V and I-V curves have been investigated and the effects of un-doped ZnTe layer thickness as well as annealing temperatures on I-V characteristics of CdTe solar cells have been studied. The results show that the “roll over” and “cross over” phenomena of dark and light I-V curves can be eliminated by use of ZnTe/ZnTe:Cu layer and the fill factor for a typical sample has increased to 73%, where there is no high resistance transparent layer. The reasons have been discussed combined with the energy band diagram of CdTe solar cells.

  4. CdTe Nanowires studied by Transient Absorption Microscopy

    Directory of Open Access Journals (Sweden)

    Kuno M.

    2013-03-01

    Full Text Available Transient absorption measurements were performed on single CdTe nanowires. The traces show fast decays that were assigned to charge carrier trapping at surface states. The observed power dependence suggests the existence of a trap-filling mechanism. Acoustic phonon modes were also observed, which were assigned to breathing modes of the nanowires. Both the fundamental breathing mode and the first overtone were observed, and the dephasing times provide information about how the nanowires interact with their environment.

  5. Simulation of charge transport in pixelated CdTe

    OpenAIRE

    Kolstein, M.; G Ariño; Chmeissani, M.; De Lorenzo, G.

    2014-01-01

    The Voxel Imaging PET (VIP) Pathfinder project intends to show the advantages of using pixelated semiconductor technology for nuclear medicine applications to achieve an improved image reconstruction without efficiency loss. It proposes designs for Positron Emission Tomography (PET), Positron Emission Mammography (PEM) and Compton gamma camera detectors with a large number of signal channels (of the order of 106). The design is based on the use of a pixelated CdTe Schottky detector to have op...

  6. Magnetization dynamics in (Cd,Mn)Te quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Goryca, M.; Nawrocki, M. [Institute of Experimental Physics, Warsaw University, Hoza 69, 00-681 Warsaw (Poland); Ferrand, D.; Tatarenko, S. [Joined group ' ' Nanophysique et semiconducteurs' ' , CNRS/CEA/Universite Joseph Fourier-Grenoble, Laboratoire de Spectrometrie Physique, BP 87, 38402 Saint Martin d' Heres cedex (France); Kossacki, P.; Pacuski, W.; Maslana, W. [Institute of Experimental Physics, Warsaw University, Hoza 69, 00-681 Warsaw (Poland); Joined group ' ' Nanophysique et semiconducteurs' ' , CNRS/CEA/Universite Joseph Fourier-Grenoble, Laboratoire de Spectrometrie Physique, BP 87, 38402 Saint Martin d' Heres cedex (France); Cibert, J. [Laboratoire Louis Neel, CNRS, BP166, 38042 Grenoble cedex 9 (France)

    2006-03-15

    The relaxation of the magnetization change induced by a short pulse of magnetic field in p-doped (Cd,Mn)Te quantum wells is determined from the giant Zeeman shift of the photoluminescence line. The characteristic times change by three orders of magnitude upon application of a static magnetic field. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  7. Physical properties of Bi doped CdTe thin films grown by the CSVT method

    Energy Technology Data Exchange (ETDEWEB)

    Vigil-Galan, O.; Sastre-Hernandez, J.; Cruz-Gandarilla, F.; Aguilar-Hernandez, J.; Contreras-Puente, G.; Tufino-Velazquez, M. [Escuela Superior de Fisica y Matematicas, Instituto Politecnico Nacional, 07738 Mexico D. F. (Mexico); Marin, E. [Centro de Investigacion en Ciencia Aplicada y Tecnologia Avanzada, Instituto Politecnico Nacional, 11500 Mexico, D. F. (Mexico); Saucedo, E.; Ruiz, C.M.; Bermudez, V. [Departamento de Fisica de Materiales, Universidad Autonoma de Madrid, 28049 Madrid (Spain)

    2006-09-22

    A study of the physical properties of CdTe thin films doped with Bi is presented. CdTe:Bi thin films were deposited by the close space vapor transport (CSVT) technique using powdered CdTe:Bi crystals grown by the vertical Bridgman method. CdTe:Bi crystals were obtained with nominal Bi doping concentrations varying in the 1x10{sup 17}-8x10{sup 18}cm{sup -3} range. The physical properties of CdTe:Bi thin films were studied performing photoluminescence, X-ray, SEM, photoacoustic spectroscopy and resistivity measurements. We observed a decrease of the resistivity values of CdTe:Bi films with the Bi content as low as 6x10{sup 5}{omega}-cm for Bi concentrations of 8x10{sup 18}cm{sup -3}. These are meaningful results for CdTe-based solar cells. (author)

  8. Effects of Antimony Doping in Polycrystalline CdTe Thin-Film Solar Cells

    Science.gov (United States)

    Okamoto, Tamotsu; Ikeda, Shigeyuki; Nagatsuka, Satsuki; Hayashi, Ryoji; Yoshino, Kaoru; Kanda, Yohei; Noda, Akira; Hirano, Ryuichi

    2012-10-01

    The effects of antimony (Sb) doping of the CdTe layer in the CdTe solar cells were investigated using Sb-doped CdTe powders as source materials for CdTe deposition by the close-spaced sublimation (CSS) method. Conversion efficiency increased with increasing Sb concentration below 1×1018 cm-3, mainly owing to the improvement of the fill factor. Secondary ion microprobe mass spectrometry (SIMS) depth profile revealed that the Sb impurities at a concentration of approximately 1×1016 cm-3 were incorporated into the CdTe layer when using the Sb-doped CdTe source of 1×1018 cm-3. The observation of surface morphology showed that the grain sizes were improved by Sb addition. Therefore, the improved performance upon Sb addition to CdTe solar cells was probably due to the improvements in crystallinity, such as increased grain size.

  9. Close space sublimation of CdTe for solar cells and the effect of underlying layers

    OpenAIRE

    Wakeling, B. R.

    2010-01-01

    This work has focused on the design, construction and testing of a close space sublimation system for CdTe deposition. In addition, it also focused on variations to the treatment and fabrication procedures of the transparent conducting oxide and CdS layers prior to the CdTe deposition, in order to influence the structure and electrical properties of the CdTe/CdS interface. CdTe was deposited by the physical vapour process, close space sublimation. The equipment used was custom built for this ...

  10. One-Pot Aqueous Phase Synthesis of CdTe and CdTe/ZnS Core/Shell Quantum Dots.

    Science.gov (United States)

    Zhou, Beiying; Yang, Fengjiu; Zhang, Xin; Cheng, Wenyan; Luo, Wei; Wang, Lianjun; Jiang, Wan

    2016-06-01

    A facile and economical one-pot strategy has been developed for the synthesis of water-solute CdTe and CdTe/ZnS core/shell quantum dots (QDs) using tellurium dioxide (TeO2) as a tellurium precursor and thioglycolic acid (TGA) as stabilizer without any pre-treatment and inert atmosphere protection. As-synthesized QDs were characterized by transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), electron diffraction spectroscopy (EDS), X-ray powder diffraction (XRD), UV-vis and photoluminescence (PL). The spherical particles were uniformly distributed with the average diameters of 3.2 nm (CdTe QDs) and -5 nm (CdTe/ZnS QDs). By altering the reaction conditions, the emission wavelengths of the CdTe core QDs and CdTe/ZnS core/shell QDs could be tuned from 508 to 574 nm and 526 to 600 nm with narrow full widths at half maximum (FWHM) of 33 to 58 nm, respectively. Meanwhile, on the optimum condition, the luminescence efficiency of CdTe/ZnS QDs can achieve to 74%, which was higher than that of CdTe core QDs (24%).

  11. 12% efficient CdTe/CdS thin film solar cells deposited by low-temperature close space sublimation

    Science.gov (United States)

    Schaffner, Judith; Motzko, Markus; Tueschen, Alexander; Swirschuk, Andreas; Schimper, Hermann-Josef; Klein, Andreas; Modes, Thomas; Zywitzki, Olaf; Jaegermann, Wolfram

    2011-09-01

    We report 12% efficient CdS/CdTe thin film solar cells prepared by low temperature close space sublimation (CSS). Both semiconductor films, CdS and CdTe, were deposited by high vacuum CSS in superstrate configuration on glass substrates with fluorine doped tin oxide (FTO) front contact. The CdTe deposition was carried out at a substrate temperature (Tsub) of ≤340 ∘C, which is much lower than that used in conventional processes (>500 ∘C). The CdTe films were treated with the usual CdCl2 activation process. Different optimal annealing times and temperatures were found for low-temperature cells (Tsub≤ 340 ∘C) compared to high-temperature cells (Tsub = 520 ∘C). The influence of the activation step on the morphology of high-temperature and low-temperature CdTe is determined by XRD, AFM, SEM top views, and SEM cross-sections. Grain growth, strong recrystallization, and a reduction of planar defects during the activation step are observed, especially for low-temperature CdTe. Further, the influence of CdS deposition parameters on the solar cell performance is investigated by using three different sets of parameters with different deposition rates and substrate temperatures for the CdS preparation. Efficiencies about 10.9% with a copper-free back contact and 12.0% with a copper-containing back contact were achieved using the low temperature CdTe process.

  12. Interaction of CdTe/CdS quantum dots with antibodies

    Institute of Scientific and Technical Information of China (English)

    Chen Shi; Xiang Yi Huang; Chao Qing Dong; Hong Jin Chen; Ji Cun Ren

    2009-01-01

    In the study,we observed the strong adsorption of CdTe/CdS QDs to antibodies and the formation of QDs-antibodies conjugates.Capillary electrophoresis with laser-induced fluorescence detection(CE-LIF),fluorescence spectrometry and fluorescence correlation spectroscopy(FCS)were used to characterize the QDs conjugates with antibody.We found that the QDs-antibody conjugates possessed high fluorescence,small hydrodynamic radii and good stability in aqueous solution.

  13. Performance characteristics of CdTe drift ring detector

    Science.gov (United States)

    Alruhaili, A.; Sellin, P. J.; Lohstroh, A.; Veeramani, P.; Kazemi, S.; Veale, M. C.; Sawhney, K. J. S.; Kachkanov, V.

    2014-03-01

    CdTe and CdZnTe material is an excellent candidate for the fabrication of high energy X-ray spectroscopic detectors due to their good quantum efficiency and room temperature operation. The main material limitation is associated with the poor charge transport properties of holes. The motivation of this work is to investigate the performance characteristics of a detector fabricated with a drift ring geometry that is insensitive to the transport of holes. The performance of a prototype Ohmic CdTe drift ring detector fabricated by Acrorad with 3 drift rings is reported; measurements include room temperature current voltage characteristics (IV) and spectroscopic performance. The data shows that the energy resolution of the detector is limited by leakage current which is a combination of bulk and surface leakage currents. The energy resolution was studied as a function of incident X-ray position with an X-ray microbeam at the Diamond Light Source. Different ring biasing schemes were investigated and the results show that by increasing the lateral field (i.e. the bias gradient across the rings) the active area, evaluated by the detected count rate, increased significantly.

  14. Deep level transient spectroscopy investigation of deep levels in CdS/CdTe thin film solar cells with Te:Cu back contact

    Science.gov (United States)

    Wang, Zhao; Li, Bing; Zheng, Xu; Xie, Jing; Huang, Zheng; Liu, Cai; Feng, Liang-Huan; Zheng, Jia-Gui

    2010-02-01

    Deep levels in Cds/CdTe thin film solar cells have a potent influence on the electrical property of these devices. As an essential layer in the solar cell device structure, back contact is believed to induce some deep defects in the CdTe thin film. With the help of deep level transient spectroscopy (DLTS), we study the deep levels in CdS/CdTe thin film solar cells with Te:Cu back contact. One hole trap and one electron trap are observed. The hole trap H1, localized at Ev + 0.128 eV, originates from the vacancy of Cd (VCd). The electron trap E1, found at Ec -0.178 eV, is considered to be correlated with the interstitial Cuj+ in CdTe.

  15. CdTe/Si复合衬底Ex-situ退火研究%Research of CdTe/Si composite substrate by annealing

    Institute of Scientific and Technical Information of China (English)

    刘铭; 周立庆; 巩锋; 常米; 王经纬; 王丛

    2012-01-01

    One of the main methods to reduce the HgCdTe/Si dislocation density is to reduce CdTe/Si composite substrate's dislocation density. How to improve the CdTe/Si composite substrate's crystal quality is very critical for HgCdTe/Si FPAs. The general methods to reduce CdTe/Si composite substrate dislocation density are: growth of su-perlattice buffer layer,Si substrate misorientention and annealing etc. This paper presents the result of the influence on the quality of CdTe/Si composite substrate by Ex-situ annealing. The research indicates that after Ex-situ annealing, the EPD of composite substrate can reduce to 4. 2 × 105 cm-2 ,and the FWHM can reduce to 60 arcsec.%复合衬底CdTe/ZnTe/Si的晶体质量是导致随后外延的HgCdTe外延膜高位错密度的主要原因之一,因此如何提高复合衬底CdTe/Si晶体质量是确保硅基碲镉汞走上工程化的关键所在.降低复合衬底CdTe/Si位错密度方法一般有:生长超晶格缓冲层、衬底偏向、In-situ退火和Ex-situ退火等,本文主要研究Ex-situ退火对复合衬底CdTe/Si晶体质量的影响.研究表明复合衬底经过Ex-situ退火后位错密度最好值达4.2×105 cm-2,双晶半峰宽最好值达60arcsec .

  16. Raman and RBS studies of interdiffusion in RF-sputtered CdS/CdTe solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Fischer, A.; Jayamaha, U.N.; Bykov, E.; Grecu, D.; Bohn, R.G.; Compaan, A.D. [Dept. of Physics and Astronomy, The University of Toledo, Toledo, Ohio 43606 (United States)

    1997-02-01

    The performance of CdS/CdTe photovoltaic devices is strongly determined by the properties of the CdS/CdTe interface region which forms during the heat treatment of the solar cell. Due to interdiffusion of sulfur and tellurium across the original CdS/CdTe junction and the formation of CdS{sub x}Te{sub 1{minus}x} at the interface, material properties such as the bandgap and the absorption coefficient of the newly formed material will be changed. In order to improve our understanding of the interface and to be able to control it, near resonant Raman scattering on a series of single-phase CdS{sub x}Te{sub 1{minus}x} alloys was performed and the Stokes shifts of the longitudinal optical (LO) phonons were measured over the entire composition x. The data have been fitted according to the modified random element isodisplacement (MREI) model. The results gained from the investigation of the alloys have then been applied to study the CdS/CdTe interface region of sputter-deposited solar cells. The formation of a two-phase CdS{sub x}Te{sub 1{minus}x} alloy region at the CdS-CdTe solar cell interface has been confirmed and the composition of each phase was measured. In addition, we have obtained Rutherford backscattering (RBS) spectra from thin bilayers of CdTe/CdS on fused silica, which provided information on interdiffusion with {approximately}10nm depth resolution. {copyright} {ital 1997 American Institute of Physics.}

  17. Optical, thermal and phase transition studies in Sn1–GeTe

    Indian Academy of Sciences (India)

    M Sivabharathy; N Sankar; R Saravanan; K Ramachandran

    2005-12-01

    The optical and thermal properties of the mixed semiconducting alloy, Sn1–GeTe, is studied by photo acoustics, for various Ge concentrations and phase transition for a particular concentration is also studied by the same method. The results are compared with the available literature values and discussed.

  18. Unexpected Au Alloying in Tailoring In-Doped SnTe Nanostructures with Gold Nanoparticles

    Directory of Open Access Journals (Sweden)

    Samuel Atherton

    2017-03-01

    Full Text Available Materials with strong spin-orbit interaction and superconductivity are candidates for topological superconductors that may host Majorana fermions (MFs at the edges/surfaces/vortex cores. Bulk-superconducting carrier-doped topological crystalline insulator, indium-doped tin telluride (In-SnTe is one of the promising materials. Robust superconductivity of In-SnTe nanostructures has been demonstrated recently. Intriguingly, not only 3-dimensional (3D nanostructures but also ultra-thin quasi-2D and quasi-1D systems can be grown by the vapor transport method. In particular, nanostructures with a controlled dimension will give us a chance to understand the dimensionality and the quantum confinement effects on the superconductivity of the In-SnTe and may help us work on braiding MFs in various dimensional systems for future topological quantum computation technology. With this in mind, we employed gold nanoparticles (GNPs with well-identified sizes to tailor In-SnTe nanostructures grown by vapor transport. However, we could not see clear evidence that the presence of the GNPs is necessary or sufficient to control the size of the nanostructures. Nevertheless, it should be noted that a weak correlation between the diameter of GNPs and the dimensions of the smallest nanostructures has been found so far. To our surprise, the ones grown under the vapor–liquid–solid mechanism, with the use of the GNPs, contained gold that is widely and inhomogeneously distributed over the whole body.

  19. High thermoelectric performance by resonant dopant indium in nanostructured SnTe.

    Science.gov (United States)

    Zhang, Qian; Liao, Bolin; Lan, Yucheng; Lukas, Kevin; Liu, Weishu; Esfarjani, Keivan; Opeil, Cyril; Broido, David; Chen, Gang; Ren, Zhifeng

    2013-08-13

    From an environmental perspective, lead-free SnTe would be preferable for solid-state waste heat recovery if its thermoelectric figure-of-merit could be brought close to that of the lead-containing chalcogenides. In this work, we studied the thermoelectric properties of nanostructured SnTe with different dopants, and found indium-doped SnTe showed extraordinarily large Seebeck coefficients that cannot be explained properly by the conventional two-valence band model. We attributed this enhancement of Seebeck coefficients to resonant levels created by the indium impurities inside the valence band, supported by the first-principles simulations. This, together with the lower thermal conductivity resulting from the decreased grain size by ball milling and hot pressing, improved both the peak and average nondimensional figure-of-merit (ZT) significantly. A peak ZT of ∼1.1 was obtained in 0.25 atom % In-doped SnTe at about 873 K.

  20. Recent advances in Tl Br, Cd Te and CdZnTe semiconductor radiation detectors: a review

    Energy Technology Data Exchange (ETDEWEB)

    Oliveira, Icimone B. [Universidade Bandeirante (UNIBAN), Sao Paulo, SP (Brazil)

    2011-07-01

    The success in the development of radiation spectrometers operating at room temperature is based on many years of effort on the part of large numbers of workers around the world. These individuals have contributed to the understanding of the fundamental materials issues associated with the growth of semiconductors for this application, the development of device fabrication and processing technology, and advances in low noise electronics and pulse processing. Progress in this field continues at an accelerated pace, as in evidenced by the improvements in detector performance and by the growing number of commercial products. Thus, the last years have been seen continued effort in the development of room temperature compound semiconductors devices. High-Z compound semiconductor detectors has been explored for high energy resolution, high detection efficiency and are of low cost. Compound semiconductors detectors are well suited for addressing needs of demanding applications such as bore hole logging where high operating temperature are encountered. In this work recent developments in semiconductors detectors were reviewed. This review concentrated on thallium bromide (TlBr), cadmium zinc telluride (CdZnTe) and cadmium telluride (CdTe) crystals detectors. TlBr has higher stopping power compared to common semiconductor materials because it has the higher photoelectric and total attenuation coefficients over wide energy range from 100 keV to 1 MeV. CdTe and CdZnTe detectors have several attractive features for detecting X-ray and low energy gamma ray. Their relatively large band gaps lead to a relatively low leakage current and offer an excellent energy resolution at room temperature. A literature survey and bibliography was also included. (author)

  1. Correlation of Interfacial Transportation Properties of CdS/CdTe Heterojunction and Performance of CdTe Polycrystalline Thin-Film Solar Cells

    Directory of Open Access Journals (Sweden)

    Guanggen Zeng

    2015-01-01

    Full Text Available The light and dark output performances of CdS/CdTe solar cells made by close-spaced sublimation (CSS were investigated to elucidate the transportation properties of carriers at CdS/CdTe heterojunction interface. It has been found that the interfacial transportation properties were relatively sensitive to variations of the characteristics of heterojunction due to the series resistance and shunting effects. For the high quality cell with 12.1% efficiency, narrow depletion region of ~1.1 microns and large electric field intensity of ~1.3 V/μm allow the sufficient energy-band bending close to CdS layer at CdS/CdTe heterojunction, which changes the carrier transportation mechanism from emission to diffusion and leads to the optimal rectifying characteristics with small dark saturation current density ~6.4 × 10−10 A/cm2. As a result, the schematic diagram of heterojunction band structure corresponding to various performances of solar cells has also been presented.

  2. Characterization and Modeling of CdS/CdTe Heterojunction Thin-Film Solar Cell for High Efficiency Performance

    OpenAIRE

    Hamid Fardi; Fatima Buny

    2013-01-01

    Device simulation is used to investigate the current-voltage efficiency performance in CdTe/CdS photovoltaic solar cell. The role of several limiting factors such as back contact Schottky barrier and its relationship to the doping density and layer thickness is examined. The role of surface recombination velocity at back contact interface and extended CdTe layer is included. The base CdS/CdTe experimental device used in this study shows an efficiency of 16-17%. Simulation analysis is used to ...

  3. Influence of deposition parameters on the properties of CdTe films deposited by close spaced sublimation

    Directory of Open Access Journals (Sweden)

    Vivienne Denise Falcão

    2006-03-01

    Full Text Available CdTe thin films are used as absorber layer in CdS/CdTe solar cells. The microstructure of this absorber layer plays a fundamental role in photovoltaic conversion and can be controlled by the deposition parameters used during the film growth. In this work, CdTe thin films were deposited by the CSS method onto glass substrates previously covered with In2O3:Sn. The effects of pressure, source temperature and substrate temperature on the microstructural properties of the films were studied. The properties were mainly influenced by the pressure, the presence of oxygen in the reaction chamber, and the substrate temperature. For films deposited under an argon atmosphere, an increase in grain size and a reduction of the texture were observed as the pressure and substrate temperature were increased. The introduction of oxygen in the atmosphere led to a decrease in the deposition rate and affected the microstructure and composition of the film. Films deposited under an argon-oxygen atmosphere have smaller grains than those deposited under argon and are richer in Te. The addition of oxygen to the atmosphere apparently did not result in the formation of oxides.

  4. Prospects of Back Surface Field Effect in Ultra-Thin High-Efficiency CdS/CdTe Solar Cells from Numerical Modeling

    OpenAIRE

    Nowshad Amin; Matin, M.A.; Aliyu, M. M.; M. A. Alghoul; Karim, M. R.; K. Sopian

    2010-01-01

    Polycrystalline CdTe shows greater promises for the development of cost-effective, efficient, and reliable thin film solar cells. Results of numerical analysis using AMPS-1D simulator in exploring the possibility of ultrathin, high efficiency, and stable CdS/CdTe cells are presented. The conventional baseline case structure of CdS/CdTe cell has been explored with reduced CdTe absorber and CdS window layer thickness, where 1 μm thin CdTe and 50 nm CdS layers showed reasonable efficiencies over...

  5. Carrier transfer and thermal escape in CdTe/ZnTe quantum dots.

    Science.gov (United States)

    Man, Minh Tan; Lee, Hong Seok

    2014-02-24

    We report on the carrier transfer and thermal escape in CdTe/ZnTe quantum dots (QDs) grown on a GaAs substrate. The significant emission-energy-dependent decay time at high excitation intensity (35 W/cm2) is attributed to the lateral transfer of carriers in the QDs. At low temperature (thermally activated transition occurs between two different states separated by approximately 9 meV, while the main contribution to nonradiative processes is the thermal escape from QDs that is assisted by carrier scattering via the emission of longitudinal phonons through the excited QD states at high temperature, with energies of approximately 19 meV.

  6. Heterostructures with CdTe/ZnTe quantum dots for single photon emitters grown by molecular beam epitaxy

    Science.gov (United States)

    Sorokin, S. V.; Sedova, I. V.; Gronin, S. V.; Belyaev, K. G.; Rakhlin, M. V.; Toropov, A. A.; Mukhin, I. S.; Ivanov, S. V.

    2016-12-01

    We report on the molecular beam epitaxy (MBE) of heterostructures with CdTe/ZnTe quantum dots (QDs) with relatively low surface density, which could be used as single-photon emitters. The QDs were formed on the surface of a 3.1- to 4.5-monolayer-thick two-dimensional strained CdTe layer by depositing amorphous Te layer and its fast thermal desorption. Subsequent thermal annealing of the surface with QDs in the absence of external Te flux led to strong broadening and short-wavelength shift of the QD photoluminescence (PL) peak. Measurement of the micro-PL spectra of individual CdTe/ZnTe quantum dots in fabricated mesastructures with a diameter of 200—1000 nm allowed estimation of the QD surface density as 1010 cm-2.

  7. Deposition of Cl-doped CdTe polycrystalline films by close-spaced sublimation

    Energy Technology Data Exchange (ETDEWEB)

    Okamoto, Tamotsu; Takahashi, Kohei; Akiba, Sho; Yasuda, Nao [Department of Electrical and Electronic Engineering, National Institute of Technology, Kisarazu College, 2-11-1 Kiyomidai-higashi, Kisarazu, Chiba 292-0041 (Japan); Tokuda, Satoshi; Kishihara, Hiroyuki; Ichioka, Akina; Doki, Takahiro; Sato, Toshiyuki [Technology Research Laboratory, Shimadzu Corporation, 3-9-4 Hikaridai, Seika-cho, Soraku-gun, Kyoto 619-0237 (Japan)

    2015-06-15

    The effects of Cl-doping on the CdTe layers by the close-spaced sublimation (CSS) deposition were investigated. Cl-doped CdTe polycrystalline films were deposited on graphite substrates by CSS method using a mixture of CdTe and CdCl{sub 2} powder as a source. In X-ray diffraction (XRD) patterns of the obtained films with various deposition times, many diffraction peaks other than CdTe peaks were observed in the deposition times lower than 10 min. These diffraction peaks were probably due to the formation of chlorides of Cd, Te and C, such as CdCl{sub 2}, TeCl{sub 4}, Te{sub 3}Cl{sub 2} and C{sub 10}Cl{sub 8}. X-ray fluorescence (XRF) and secondary ion mass spectrometry (SIMS) analyses revealed that a large amount of chlorine was contained in the films with the deposition times lower than 10 min, and that Cl concentration decreased with increasing the deposition time above 3 min. These results indicate that the films containing the chlorides of Cd, Te and C in addition to CdTe are formed in the initial stage of the CSS deposition using a mixture of CdTe and CdCl{sub 2} powder as a source. Cross-sectional images revealed that the grain size was decreased by the effect of Cl-doping. Furthermore, current-voltage (I -V) characteristics of the CdTe/graphite structures were measured, and it was found that the resistivity of the Cl-doped CdTe layer was much higher than that of the undoped CdTe layer. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  8. A comparative study on the sensitive detection of hydroxyl radical using thiol-capped CdTe and CdTe/ZnS quantum dots.

    Science.gov (United States)

    Adegoke, Oluwasesan; Nyokong, Tebello

    2012-11-01

    Four types of water-soluble luminescent quantum dots (QDs) whose surface was functionlaized with thioglycolic acid (TGA), 3-mercaptopropionic acid (MPA), or glutathione (GSH), were investigated for the sensitive and selective detection of hydroxyl radical (·OH) in aqueous media. It was found that the type of capping agent and QD influenced the sensitivity of the probe. The order of sensitivity of the probe was: GSH-CdTe@ZnS > MPA-CdTe@ZnS > TGA-CdTe > MPA-CdTe QDs. Under the optimum conditions, a limit of detection as low as 8.5 × 10(-8) M was obtained using GSH-CdTe@ZnS. The effects of foreign reactive oxygen species and the Fenton reactants and products as possible interferences on the proposed probe were negligible for CdTe@ZnS QDs. Besides, experimental results indicated that CdTe@ZnS QDs were more attractive for the selective recognition of ·OH than CdTe QDs. The mechanistic reaction pathway between the QDs and ·OH is proposed.

  9. Catalyst- and template-free low-temperature in situ growth of n-type CdS nanowire on p-type CdTe film and p-n heterojunction properties

    Science.gov (United States)

    Ma, Ligang; Liu, Wenchao; Cai, Hongling; Zhang, Fengming; Wu, Xiaoshan

    2016-12-01

    CdS is an important semiconductor used in optoelectronic devices. Simple techniques for growing CdS nanostructures are thus essential at a low cost. This study presents a novel method for growing single-crystal n-type CdS nanowires on p-type CdTe films by thermal annealing in an H2S/N2 mixed gas flow, which does not require the help of a catalyst or template. The formation process and growth mechanism of the nanowires are investigated. Well-dispersed whiskerlike CdS nanostructures are obtained at an appropriate annealing temperature and duration. We suggest that the stress-driving mechanism of nanowire formation may contribute to the growth of CdS nanowires, and that the evaporation of Te through the boundaries of the CdS grain seeds plays an important role in the sustainable growth of nanowire. In addition, CdS/CdTe heterojunction device is fabricated on Mo glass. The I-V characteristic of the heterojunction in dark shows typical rectifying diode behavior. The turn-on voltage can be regulated by annealing conditions. Meanwhile, the obvious photovoltaic effect is obtained on the in situ growth heterojunction prepared at low annealing temperature. Hence, this is a new fabricated method for CdTe-based materials in the field of energy conversion.

  10. Post-growth CdCl₂ treatment on CdTe thin films grown on graphene layers using a close-spaced sublimation method.

    Science.gov (United States)

    Jung, Younghun; Yang, Gwangseok; Chun, Seungju; Kim, Donghwan; Kim, Jihyun

    2014-05-05

    We investigated the morphological, structural and optical properties of CdCl₂-treated cadmium telluride (CdTe) thin films deposited on defective graphene using a close-spaced sublimation (CSS) system. Heat treatment in the presence of CdCl₂ caused recrystallization of CSS-grown CdTe over the as-deposited structures. The preferential (111) orientation of as-deposited CdTe films was randomized after post-growth CdCl₂ treatment. New small grains (bumps) on the surface of CdCl₂-treated CdTe films were ascribed to nucleation of the CdTe grains during the CdCl₂ treatment. The properties of as-deposited and CdCl₂-treated CdTe films were characterized by room temperature micro-photoluminescence, micro-Raman spectroscopy, scanning electron microscopy, and X-ray diffraction analysis. Our results are useful to demonstrate a substrate configuration CdTe thin film solar cells.

  11. CdS/Cd Te solar cells. Part I. Solar cells processed by the gradient recrystallization and growth technique (GREG); Celdas solares de heterounion de CdS/CdTe. Parte I. Celdas solares procesadas por la tecnica GREG

    Energy Technology Data Exchange (ETDEWEB)

    Tufino V, M.; Contreras P, G.; Albor A, M.L.; Gonzalez T, M.A. [Escuela Superior de Fisica y Matematicas, Instituto Politecnico Nacional , 07738 Mexico D.F. (Mexico); Compaan, A.D. [Department of Physics and Astronomy and Center for Materials Science and Engineering, The University of Toledo, Toledo OH 43606 (United States)

    1998-12-31

    In this paper we present the processing and characterization of thin film CdS/Cd Te solar cells obtained by the gradient recrystallization and growth technique, GREG. The cells were deposited on soda-lime LOF{sup TM} conducting glass substrates and Cu-Au contacts were evaporated on top of the Cd Te film. The films deposition conditions were: for CdS the source temperature T{sub f} varied between 750 and 800 Centigrade and the substrate temperature T{sub s} varied between 480 and 550 Centigrade, while for Cd Te T{sub f} varied between 570 and 650 Centigrade and T{sub s} from 460 to 480 Centigrade; both films were deposited under a constant Ar gas pressure. The films were characterized by X-ray diffraction, atomic force microscopy, optical absorption and photoluminescence . Both CdS and Cd Te films were polycrystalline with preferential orientation in the (002) direction for CdS and in the (111) direction for Cd Te; the grain size ranges for the films were 0.2-1 {mu} m for CdS and 0.5-5 {mu} m for Cd Te. The solar cell photoconductive parameters were determined yielding the best cell performance values of V{sub OC} = 0.7 V, J{sub SC} = 31 m A/cm{sup 2} , f f = 50% , SQE{sub max} = 0.6 elect./photon at 550 nm and 8 % solar energy conversion efficiency. (Author)

  12. Carrier concentration dependence of structural disorder in thermoelectric Sn1−xTe

    Directory of Open Access Journals (Sweden)

    Mattia Sist

    2016-09-01

    Full Text Available SnTe is a promising thermoelectric and topological insulator material. Here, the presumably simple rock salt crystal structure of SnTe is studied comprehensively by means of high-resolution synchrotron single-crystal and powder X-ray diffraction from 20 to 800 K. Two samples with different carrier concentrations (sample A = high, sample B = low have remarkably different atomic displacement parameters, especially at low temperatures. Both samples contain significant numbers of cation vacancies (1–2% and ordering of Sn vacancies possibly occurs on warming, as corroborated by the appearance of multiple phases and strain above 400 K. The possible presence of disorder and anharmonicity is investigated in view of the low thermal conductivity of SnTe. Refinement of anharmonic Gram–Charlier parameters reveals marginal anharmonicity for sample A, whereas sample B exhibits anharmonic effects even at low temperature. For both samples, no indications are found of a low-temperature rhombohedral phase. Maximum entropy method (MEM calculations are carried out, including nuclear-weighted X-ray MEM calculations (NXMEM. The atomic electron densities are spherical for sample A, whereas for sample B the Te electron density is elongated along the 〈100〉 direction, with the maximum being displaced from the lattice position at higher temperatures. Overall, the crystal structure of SnTe is found to be defective and sample-dependent, and therefore theoretical calculations of perfect rock salt structures are not expected to predict the properties of real materials.

  13. Characterization of Highly Efficient CdTe Thin Film Solar Cells by Low-Temperature Photoluminescence

    Science.gov (United States)

    Okamoto, Tamotsu; Matsuzaki, Yuichi; Amin, Nowshad; Yamada, Akira; Konagai, Makoto

    1998-07-01

    Highly efficient CdTe thin film solar cells prepared by close-spaced sublimation (CSS) method with a glass/ITO/CdS/CdTe/Cu-doped carbon/Ag structure were characterized by low-temperature photoluminescence (PL) measurement. A broad 1.42 eV band probably due to VCd Cl defect complexes appeared as a result of CdCl2 treatment. CdS/CdTe junction PL revealed that a CdSxTe1-x mixed crystal layer was formed at the CdS/CdTe interface region during the deposition of CdTe by CSS and that CdCl2 treatment promoted the formation of the mixed crystal layer. Furthermore, in the PL spectra of the heat-treated CdTe after screen printing of the Cu-doped carbon electrode, a neutral-acceptor bound exciton (ACu0, X) line at 1.590 eV was observed, suggesting that Cu atoms were incorporated into CdTe as effective acceptors after the heat treatment.

  14. Nanowire CdS-CdTe Solar Cells with Molybdenum Oxide as Contact

    OpenAIRE

    Hongmei Dang; Singh, Vijay P

    2015-01-01

    Using a 10 nm thick molybdenum oxide (MoO3−x) layer as a transparent and low barrier contact to p-CdTe, we demonstrate nanowire CdS-CdTe solar cells with a power conversion efficiency of 11% under front side illumination. Annealing the as-deposited MoO3 film in N2 resulted in a reduction of the cell’s series resistance, from 9.97 Ω/cm2 to 7.69 Ω/cm2, and increase in efficiency from 9.9% to 11%. Under illumination from the back, the MoO3−x/Au side, the nanowire solar cells yielded Jsc of 21 mA...

  15. Phase equilibria and liquid phase epitaxy growth of PbSnSeTe lattice matched to PbSe

    Science.gov (United States)

    Mccann, Patrick J.; Fonstad, Clifton G.; Fuchs, Jacob; Feit, Ze'ev

    1987-01-01

    The necessary phase diagram data for growing lattice-matched layers of PbSnSeTe on PbSe are presented. Solid compounds of Pb(1-x)Sn(x)Se(1-y)Te(y) lattice-matched to PbSe were grown from liquid melts consisting of (Pb/1-x/Sn/x/)(1-z)(Se/1-y/Te/y/)(z); phase equilibria data were determined together with liquidus data for values of x(liquid) from 0 to 40 percent and y(liquid) from 0 to 40 percent for temperatures between 450 and 540 C. It was found that relatively large amounts of Te must be added to the melt to achieve lattice matching because of its low segregation coefficient relative to Se. A significant lattice-pulling effect was discovered for the 5-percent Sn case, and a similar effect is expected for the 10- and 20-percent Sn cases.

  16. Catalytic growth of CdTe nanowires by closed space sublimation method

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Gwangseok; Jung, Younghun [Department of Chemical and Biological Engineering, Korea University, Seoul 136-701 (Korea, Republic of); Chun, Seungju; Kim, Donghwan [Department of Materials Science and Engineering, Korea University, Seoul 136-701 (Korea, Republic of); Kim, Jihyun, E-mail: hyunhyun7@korea.ac.kr [Department of Chemical and Biological Engineering, Korea University, Seoul 136-701 (Korea, Republic of)

    2013-11-01

    CdTe nano-/micro-structures with various morphologies were grown by using the closed space sublimation (CSS) method on a sapphire substrate by Au-catalyzed vapor–liquid–solid (VLS) mechanism. Length, diameter, and morphology of the CdTe nano-/micro-structures depended on the growth time and temperature gradient between the substrate and powdered CdTe source. Scanning electron microscopy images showed that an Au catalyst droplet existed at the tips of CdTe nanowires, which confirms that CdTe nanowires were grown by an Au-catalyzed VLS mechanism. Also, we observed that the two-dimensional CdTe film layer initially formed before the growth of the CdTe nano-/micro-wires. The optical and structural properties of CdTe nano-/micro-structures were characterized by X-ray diffraction technique and micro-Raman spectroscopy. Our study demonstrates that diverse CdTe nano-/micro-structures can be fabricated by using Au-catalyzed VLS growth process in a simple CSS chamber by controlling the temperature gradient and growth time. - Highlights: • We demonstrated CdTe nanowires using closed space sublimation method. • Au-catalyst droplets at the tips confirmed vapor–liquid–solid mechanism. • Diameters and lengths increased with increasing temperature gradient and time.

  17. Compensation models in chlorine doped CdTe based on positron annihilation and photoluminescence spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Stadler, W.; Hofman, D.M.; Meyer, B.K. [Technische Universitaet Muenchen, Garching (Germany); Krause-Rehberg, R.; Polity, A.; Abgarjan, Th. [Martin-Luther Universitaet Halle-Wittenberg, FB Physik, Halle (Germany); Salk, M.; Benz, K.W. [Kristallographisches Institut, Universitaet Freiburg, Freiburg (Germany); Azoulay, M. [Soreq, Nuclear Research Centre, Yavne (Israel)

    1995-12-31

    In this investigation positron annihilation, photoluminescence and electron paramagnetic resonance techniques are employed to gain insight in the compensation of CdTe doped with the halogen Cl. We will demonstrate that the high resistivity of CdTe:Cl cannot be explain by the interaction between the shallow effective mass type donor Cl on Te site and the doping induced shallow acceptor complex, a Cd vacancy paired off with a nearest-neighbour Cl atom (A centre). From electron paramagnetic resonance investigations we conclude that the mid gap trap, often detected by electrical methods in CdTe, is not the isolated Cd vacancy. (author). 9 refs, 2 figs, 1 tab.

  18. Automatic Control System for the High Pressure CdTe Crystal Growth Furnace

    OpenAIRE

    Petr Praus; Eduard Belas; Jiri Bok; Roman Fesh; Jan Franc; Pavel Hoschl

    2006-01-01

    CdTe and (CdZn)Te bulk single crystals have been widely used as substrates for MBE and LPE epitaxy of infrared (HgCd)Te as well as gamma- and X-ray detectors. The Cd1-xZnxTe (x = 0.04-0.1) single crystals with diameter up to 100 mm and height at most 40 mm were prepared in our laboratory in a vertical arrangement by gradual cooling of the melt (the Vertical Gradient Freezing method). Achievement of excellent crystal quality required full control of Cd pressure during the growth process and ap...

  19. A study of vapor CdCl{sub 2} treatment by CSS in CdS/CdTe solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Rios-Flores, A.; Pena, J.L.; Castro-Pena, V.; Ares, O.; Castro-Rodriguez, R. [Applied Physics Department, CINVESTAV-IPN Merida, C.P. 97310 Merida, Yucatan (Mexico); Bosio, A. [University of Parma, Department of Physics, v.le G.P. Usberti 7/A, 43100 Parma (Italy)

    2010-06-15

    We report the effect of CdCl{sub 2} vapor treatment on the photovoltaic parameters of CdS/CdTe solar cells. Vapor treatment allows combining CdCl{sub 2} exposure time and annealing in one step. In this alternative treatment, the CdS/CdTe substrates were treated with CdCl{sub 2} vapor in a close spaced sublimation (CSS) configuration. The substrate temperature and CdCl{sub 2} powder source temperature were 400 C. The treatment was done by varying the treatment time (t) from 15 to 90 min. Such solar cells are examined by measuring their current density versus voltage (J-V) characteristics. The open-circuit voltage (V{sub oc}), short circuit current density (J{sub sc}) and fill factor (FF) of our best cell, fabricated and normalized to the area of 1 cm{sup 2}, were V{sub oc} = 663 mV, J{sub sc} = 18.5 mA/cm{sup 2} and FF = 40%, respectively, corresponding to a total area conversion efficiency of {eta} = 5%. In cells of minor area (0.1 cm{sup 2}) efficiencies of 8% have been obtained. (author)

  20. The Analysis of Structure and Morphology for Big Area CdTe/CdZnTe/Si Thin Film Grown by HWE Technique%HWE生长大面积CdTe/CdZnTe/Si薄膜的结构和形貌分析

    Institute of Scientific and Technical Information of China (English)

    杨爱明; 吴长树; 杨宇; 唐利斌

    2004-01-01

    用热壁外延法(HWE)生长直径30mm的CdTe/CdZnTe/Si薄膜,经XRD测试说明它是晶面为(111)取向的立方闪锌矿结构.SEM对Si衬底、CdZnTe缓冲层和CdTe薄膜三层分别测试,结果发现:Si衬底表面结构粗糙,CdZnTe缓冲层较Si衬底表面结构细致,CdTe薄膜较CdZnTe缓冲层表面结构光滑细密,即缺陷较CdZnTe缓冲层少很多.通过对该片子照像看出其表面如镜面.由此说明大面积CdTe/CdZnTe/Si薄膜可用HWE技术制备.

  1. The effects of CdS processing and glass substrates on the performance of CdTe solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Ferekides, C.S.; Dugan, K.; Ceekala, V.; Killian, J.; Oman, D.; Swaminathan, R.; Morel, D.L. [Univ. of South Florida, Tampa, FL (United States). Dept. of Electrical Engineering

    1994-12-31

    Cadmium Sulfide films prepared by rf sputtering and close spaced sublimation (CSS) have been used for the fabrication of CdTe/CdS thin film solar cells on borosilicate glass substrates. The CdTe layer was prepared by CSS at high processing temperatures (600 C). CdS films prepared by the chemical bath deposition process (CBD) were deposited on tin oxide coated soda lime glass substrates. For these devices the CSS CdTe films were prepared at low substrate temperatures (< 550 C). Devices prepared at low processing temperatures (CdTe-CSS/CdS-CBD) on soda lime glass substrates exhibited efficiencies in excess of 13% as measured under AM 1.5 conditions at the National Renewable Energy Laboratory.

  2. On the doping problem of CdTe films: The bismuth case

    Energy Technology Data Exchange (ETDEWEB)

    Vigil-Galan, O. [Escuela Superior de Fisica y Matematicas del IPN, Edif. 9, UPALM, 07738 Mexico, D. F. (Mexico); Brown, M. [Department of Physics and Astronomy, The University of Toledo, 43606 Toledo, OH (United States); Ruiz, C.M. [Depto. Fisica de Materiales, Universidad Autonoma de Madrid, 28049 Madrid (Spain); Vidal-Borbolla, M.A. [Instituto de Investigacion en Comunicacion Optica, Av. Karakorum 1470, Lomas 4a. Secc., 78210 San Luis Potosi, SLP (Mexico); Ramirez-Bon, R. [CINVESTAV-IPN, U. Queretaro, Libramiento Norponiente No. 2000, Fracc. Real de Juriquilla, 76230 Santiago de Queretaro, Qro. (Mexico); Sanchez-Meza, E. [Escuela Superior de Fisica y Matematicas del IPN, Edif. 9, UPALM, 07738 Mexico, D. F. (Mexico); Tufino-Velazquez, M. [Escuela Superior de Fisica y Matematicas del IPN, Edif. 9, UPALM, 07738 Mexico, D. F. (Mexico)], E-mail: mtufinovel@yahoo.com.mx; Calixto, M. Estela [Escuela Superior de Fisica y Matematicas del IPN, Edif. 9, UPALM, 07738 Mexico, D. F. (Mexico); Compaan, A.D. [Department of Physics and Astronomy, The University of Toledo, 43606 Toledo, OH (United States); Contreras-Puente, G. [Escuela Superior de Fisica y Matematicas del IPN, Edif. 9, UPALM, 07738 Mexico, D. F. (Mexico)

    2008-08-30

    The controlled increase of hole concentration is an important issue and still an unsolved problem for polycrystalline CdTe-based solar cells. The typical hole concentration of as-grown CdTe thin-films goes up to 10{sup 13} cm{sup -3}, depending on the specific growth technique. The highest electron concentration obtained for CdS, the suitable window partner material of CdTe, is around 10{sup 15} cm{sup -3}. Thus, the PV-performance of a CdS/CdTe device can be optimized if the hole concentration in CdTe is increased. We have faced up this problem by studying the electrical properties of two types of CdTe films: CdTe films grown by Close Space Vapor Transport using a CdTe:Bi powder as the starting material and CdTe sputtered films doped by implantation with different Bi-doses. Temperature-dependent resistivity and Hall effect measurements and a discussion on the efficiency of both doping processes are presented.

  3. CdTe polycrystalline films on Ni foil substrates by screen printing and their photoelectric performance

    Energy Technology Data Exchange (ETDEWEB)

    Yao, Huizhen [National Key Lab of Superhard Materials, Jilin University, Changchun 130012 (China); Ma, Jinwen [College of New Energy, Bohai University, Jinzhou, Liaoning 121013 (China); Mu, Yannan [National Key Lab of Superhard Materials, Jilin University, Changchun 130012 (China); Department of Physics and Chemistry, Heihe University, Heihe 164300 (China); Su, Shi; Lv, Pin; Zhang, Xiaoling; Zhou, Liying; Li, Xue; Liu, Li; Fu, Wuyou [National Key Lab of Superhard Materials, Jilin University, Changchun 130012 (China); Yang, Haibin, E-mail: yanghb@jlu.edu.cn [National Key Lab of Superhard Materials, Jilin University, Changchun 130012 (China)

    2015-06-15

    Highlights: • The sintered CdTe polycrystalline films by a simple screen printing. • The flexible Ni foil was chose as substrates to reduce the weight of the electrode. • The compact CdTe film was obtained at 550 °C sintering temperature. • The photoelectric activity of the CdTe polycrystalline films was excellent. - Abstract: CdTe polycrystalline films were prepared on flexible Ni foil substrates by sequential screen printing and sintering in a nitrogen atmosphere for the first time. The effect of temperature on the quality of the screen-printed film was investigated in our work. The high-quality CdTe films were obtained after sintering at 550 °C for 2 h. The properties of the sintered CdTe films were characterized by scanning electron microscopy, X-ray diffraction pattern and UV–visible spectroscopy. The high-quality CdTe films have the photocurrent was 2.04 mA/cm{sup 2}, which is higher than that of samples prepared at other temperatures. Furthermore, CdCl{sub 2} treatment reduced the band gap of the CdTe film due to the larger grain size. The photocurrent of photoelectrode based on high crystalline CdTe polycrystalline films after CdCl{sub 2} treatment improved to 2.97 mA/cm{sup 2}, indicating a potential application in photovoltaic devices.

  4. Cancer Cell Targeting Using Folic Acid/Anti-HER2 Antibody Conjugated Fluorescent CdSe/CdS/ZnS-MPA and CdTe-MSA Quantum Dots.

    Science.gov (United States)

    Singh, Gurpal; Kumar, Manoj; Soni, Udit; Arora, Vikas; Bansal, Vivek; Gupta, Dikshi; Bhat, Madhusudan; Dinda, Amit K; Sapra, Sameer; Singh, Harpal

    2015-12-01

    CdSe/CdS/ZnS and CdTe quantum dots (QDs) were synthesized by successive ion layer adsorption and reaction (SILAR) technique and direct aqueous synthesis respectively using thiol stabilizers. Synthesized CdSe/CdS/ZnS and CdTe QDs stabilized with 3-mercaptopropionic acid (MPA) and mercaptosuccinic acid (MSA) were used as fluorescent labels after conjugation with folic acid (FA) and anti-HER2 antibodies. Photoluminescence quantum yield of folated CdSe/CdS/ZnS-MPA and CdTe-MSA QDs was 59% and 77% than that of non-folated hydrophilic QDs. The folate receptor-mediated delivery of folic acid-conjugated CdTe-MSA and CdSe/CdS/ZnS-MPA QDs showed higher cellular internalization as observed by confocal laser scanning microscopic studies. Folated and non-folated CdTe-MSA QDs were highly toxic and exhibited only 10% cell viability as compared to > 80% cell viability with CdSe/CdS/ZnS-MPA QDs over the concentration ranging from 3.38 to 50 pmoles. Immunohistochemistry (IHC) results of human breast cancer tissue samples showed positive results with anti-HER2 antibody conjugated CdSe/CdS/ZnS-MPA QDs with better sensitivity and specificity as compared to conventional IHC analysis using diaminobenzedene staining.

  5. Cu-doped CdS and its application in CdTe thin film solar cell

    Energy Technology Data Exchange (ETDEWEB)

    Deng, Yi [School of Automation, Wuhan University of Technology, Wuhan, Hubei 430070 (China); College of Electronic and Information Engineering, Hankou University, Wuhan, Hubei 430212 (China); Yang, Jun; Yang, Ruilong; Shen, Kai; Wang, Dezhao [Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, Anhui 230026 (China); Wang, Deliang, E-mail: eedewang@ustc.edu.cn [Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, Anhui 230026 (China); Key Laboratory of Materials for Energy Conversion, University of Science and Technology of China, Hefei, Anhui 230026 (China)

    2016-01-15

    Cu is widely used in the back contact formation of CdTe thin film solar cells. However, Cu is easily to diffuse from the back contact into the CdTe absorber layer and even to the cell junction interface CdS/CdTe. This phenomenon is generally believed to be the main factor affecting the CdTe solar cell stability. In this study Cu was intentionally doped in CdS thin film to study its effect on the microstructural, optical and electrical properties of the CdS material. Upon Cu doping, the V{sub Cd{sup −}} and the surface-state-related photoluminescence emissions were dramatically decreased/quenched. The presence of Cu atom hindered the recrystallization/coalescence of the nano-sized grains in the as-deposited CdS film during the air and the CdCl{sub 2} annealing. CdTe thin film solar cell fabricated with Cu-doped CdS window layers demonstrated much decreased fill factor, which was induced by the increased space-charge recombination near the p-n junction and the worsened junction crystalline quality. Temperature dependent current-voltage curve measurement indicated that the doped Cu in the CdS window layer was not stable at both room and higher temperatures.

  6. Study of deep level defects of n+-CdS/p-CdTe solar cells

    Science.gov (United States)

    Kharangarh, Poonam Rani

    Among various photovoltaic materials, polycrystalline cadmium telluride thin film is now the most promising material, due to its low production cost excellent stability and reliability. Current-voltage and capacitance-voltage measurements of CdTe photovoltaic devices at different temperatures can provide valuable information about non-idealities in the n-p semiconductor junction. There are certain limitations which limit the efficiency of CdTe solar cells. There is no real distinction between defects and impurities in CdTe solar cells as both act as beneficial dopants or detrimental traps unlike Si where intentional shallow dopants and traps are distinctly different. Therefore, the role of defect states on CdTe solar cell performance, the effect of processing on defect states, and simple and effective characterization techniques must be investigated and identified. In this research the thin film n+-CdS/p-CdTe solar cells made with evaporated Cu as a primary back contact, are characterized by using the temperature dependence of the reverse bias diode current (J-V-T) to determine the energy levels of deep defects. The results of the J-V-T measurements on solar cells made at NJIT show that while modest amounts of Cu enhance cell performance, an excessive high temperature annealing step degrades device quality and reduces efficiency. This work addresses the error that can be introduced during defect energy level estimation if the temperature dependence of the carrier capture cross-section is neglected. Therefore, the location of traps is derived using a Shockley-Read-Hall recombination model with modified assumptions. A Cu-related deep level defect with activation energy of 0.57eV is observed for Cu evaporated back contact cells and an intrinsic defect with activation energy 0.89eV is found. Frequency dispersion in Capacitance-Voltage measurements confirms the presence of Cu-related deep level traps for cells with a Cu evaporated back contact, whereas no such defects

  7. Synthesis of CdSe/ZnS and CdTe/ZnS Quantum Dots: Refined Digestive Ripening

    Directory of Open Access Journals (Sweden)

    Sreeram Cingarapu

    2012-01-01

    Full Text Available We report synthesis of CdSe and CdTe quantum dots (QDs from the bulk CdSe and CdTe material by evaporation/co-condensation using the solvated metal atom dispersion (SMAD technique and refined digestive ripening. The outcomes of this new process are (1 the reduction of digestive ripening time by employing ligands (trioctylphosphine oxide (TOPO and oleylamine (OA as capping agent as well as digestive ripening solvent, (2 ability to tune the photoluminescence (PL from 410 nm to 670 nm, (3 demonstrate the ability of SMAD synthesis technique for other semiconductors (CdTe, (4 direct comparison of CdSe QDs growth with CdTe QDs growth based on digestive ripening times, and (5 enhanced PL quantum yield (QY of CdSe QDs and CdTe QDs upon covering with a ZnS shell. Further, the merit of this synthesis is the use of bulk CdSe and CdTe as the starting materials, which avoids usage of toxic organometallic compounds, eliminates the hot injection procedure, and size selective precipitation processes. It also allows the possibility of scale up. These QDs were characterized by UV-vis, photoluminescence (PL, transmission electron microscopy (TEM, high-resolution transmission electron microscopy (HRTEM, X-ray photoelectron spectroscopy (XPS, and powder XRD.

  8. CdS and CdTeS quantum dot decorated TiO2 nanowires. Synthesis and photoefficiency

    Science.gov (United States)

    Medina-Gonzalez, Yaocihuatl; Xu, William Z.; Chen, Bo; Farhanghi, Nasrin; Charpentier, Paul A.

    2011-02-01

    An easy process was developed to synthesize TiO2 nanowires sensitized with CdS and CdTeS quantum dots (QDs) requiring no pretreatment of the TiO2 nanowires prior to nanoparticle generation. CdS and CdTeS nanoparticles were firstly grown by an in situ colloidal method directly onto the TiO2 surface, hence not requiring subsequent functionalization of the QDs. The resulting nanostructure assembly and composition was confirmed by transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Successful decoration of the TiO2 nanowires by the QDs was observed by TEM, while XPS spectra provided clear evidence for the coexistence of CdS and CdTeS QDs and TiO2 nanowires. The electronic structure of the TiO2 nanowires was preserved as indicated by Raman spectroscopy. Preliminary photocurrent measurements showed that inclusion of Te in CdS QDs improved the photocurrent efficiency. Compared to bare TiO2 nanowires, CdS/TiO2 nanoassemblies showed an enhancement in photocurrent efficiency of 300% while CdTeS/TiO2 presented an improvement of 350%. This study indicates that the generation of strongly anchored CdS and CdTeS QDs on a TiO2 nanowire surface is achievable without introduction of a linker molecule, whose presence is known to decrease the electron injection efficiency.

  9. Effect of Cu doping on the properties of ZnTe:Cu thin films and CdS/CdTe/ZnTe solar cells

    Science.gov (United States)

    Tang, J.; Mao, D.; Trefny, J. U.

    1997-02-01

    The effects of Cu doping concentration and post-deposition annealing treatment on the properties of ZnTe thin films were investigated in an effort to decrease the Cu doping concentration and improve the long-term stability of CdS/CdTe/ZnTe solar cells. The structural, compositional, and electrical properties were studied systematically using x-ray diffraction (XRD), electron microprobe, Hall effect and conductivity measurements. XRD measurements indicated that the crystalline phase of as-deposited and low-temperature annealed ZnTe films is dependent on Cu doping concentration. Low-Cu-doped films exhibited zincblende phase, whereas high-Cu-doped films showed wurtzite phase. After annealing at high temperature (⩾350 °C), all films exhibited zincblende structure. Electron probe microanalysis revealed a deficiency of cations in low-Cu-doped films and an excess of cations in high-Cu-doped films. Hall effect measurements revealed a dependence of hole mobility on Cu doping concentration with the highest mobility (20 cm2/Vṡs) obtained at a low Cu concentration. Carrier concentrations higher than mid-1016cm-3 were obtained at a Cu concentration of 2 at. % and relatively low annealing temperatures. Studies of the activation energy of dark conductivity suggested that intrinsic defects (e.g., Zn vacancies) are the dominant acceptors for Cu concentrations lower than 4.5 at. %. Finally, ZnTe films with Cu concentrations as low as 1 at. % were used successfully as a back contact layer in CdTe based solar cells. Fill factors over 0.70 were obtained using ZnTe films of low Cu concentrations.

  10. Electro-Plating and Characterisation of CdTe Thin Films Using CdCl2 as the Cadmium Source

    Directory of Open Access Journals (Sweden)

    Nor A. Abdul-Manaf

    2015-09-01

    Full Text Available Cadmium telluride (CdTe thin films have been successfully prepared from an aqueous electrolyte bath containing cadmium chloride (CdCl2·H2O and tellurium dioxide (TeO2 using an electrodeposition technique. The structural, electrical, morphological and optical properties of these thin films have been characterised using X-ray diffraction (XRD, Raman spectroscopy, optical profilometry, DC current-voltage (I-V measurements, photoelectrochemical (PEC cell measurement, scanning electron microscopy (SEM, atomic force microscopy (AFM and UV-Vis spectrophotometry. It is observed that the best cathodic potential is 698 mV with respect to standard calomel electrode (SCE in a three electrode system. Structural analysis using XRD shows polycrystalline crystal structure in the as-deposited CdTe thin films and the peaks intensity increase after CdCl2 treatment. PEC cell measurements show the possibility of growing p-, i- and n-type CdTe layers by varying the growth potential during electrodeposition. The electrical resistivity of the as-deposited layers are in the order of 104 Ω·cm. SEM and AFM show that the CdCl2 treated samples are more roughness and have larger grain size when compared to CdTe grown by CdSO4 precursor. Results obtained from the optical absorption reveal that the bandgap of as-deposited CdTe (1.48–1.52 eV reduce to (1.45–1.49 eV after CdCl2 treatment. Full characterisation of this material is providing new information on crucial CdCl2 treatment of CdTe thin films due to its built-in CdCl2 treatment during the material growth. The work is progressing to fabricate solar cells with this material and compare with CdTe thin films grown by conventional sulphate precursors.

  11. Extended defects in as-grown CdZnTe

    Energy Technology Data Exchange (ETDEWEB)

    Xu, L.; Bolotnikov, A.E.; Hossain, A.; Kim, K-H.; Gul, R.; Yang, G.; Camarda, G.S.; Marchini, L.; Cui, Y.; James, R.B.; Xu, Y.; Wang, T.; Jie, W.

    2010-08-01

    We characterized samples cut from different locations in as-grown CdZnTe (CZT) ingots, using Automated Infrared (IR) Transmission Microscopy and White Beam X-ray Diffraction Topography (WBXDT), to locate and identify the extended defects in them. Our goal was to define the distribution of these defects throughout the entire ingot and their effects on detectors’ performance as revealed by the pulse-height spectrum. We found the highest- and the lowest- concentration of Te inclusions, respectively, in the head and middle part of the ingot, which could serve as guidance in selecting samples. Crystals with high concentration of Te inclusions showed high leakage current and poor performance, because the accumulated charge loss around trapping centers associated with Te inclusions distorts the internal electric field, affects the carrier transport properties inside the crystal, and finally degrades the detector’s performance. In addition, other extended defects revealed by the WBXDT measurements severely reduced the detector’s performance, since they trap large numbers of electrons, leading to a low signal for the pulse-height spectrum, or none whatsoever. Finally, we fully correlated the detector’s performance with our information on the extended defects gained from both the IR- and the WBXDT-measurements.

  12. A direct solution deposition approach to CdTe thin films

    Energy Technology Data Exchange (ETDEWEB)

    Miskin, Caleb K.; Dubois-Camacho, Angela; Reese, Matthew O.; Agrawal, Rakesh

    2016-01-01

    A direct solution deposition approach to CdTe thin films is presented. The difficulty of co-dissolving Te and desirable Cd salts is overcome through a diamine-thiol solvent mixture. Thin films of densely-packed, micron-sized grains are achieved after annealing without the need for chalcogen or CdCl2 vapor treatments.

  13. Growth and characterization of Cd1-xZnxTe/ZnO heterostructures from furnace-annealed CdTe/Zn multi-stacks

    Science.gov (United States)

    Chakraborty, Monisha; Bhattacharyya, Sugata

    2015-10-01

    Cd1-xZnxTe/ZnO hetero-structures were grown on glass substrates by furnace annealing of stack-deposited CdTe/Zn/CdTe/Zn thin film multi-layers in air. The multilayered structures were annealed in furnace at various temperatures in between 350 and 600 °C. XRD results revealed that while growth of Cd1-xZnxTe compound reached saturation by 500 °C, ZnO growth geared up in between 550 and 600 °C. The band-gap values of the composite structures were less than either standard Cd1-xZnxTe or ZnO. It was because of large presence of free Zn and Cd and staggered type-II band alignment. An exponential growth was observed for the Cd1-xZnxTe particle sizes against annealing temperature. Next SEM images showed reduced surface granularity with increasing Zn percentage in Cd1-xZnxTe. SEM micrographs further revealed growth of fiber like formations of ZnO on film surface with increasing annealing temperature. ImageJ software was further used to analyse the SEM micrographs and compositional characteristics from EDX results were co-related with structural, optical and morphological results.

  14. Monte Carlo simulations of morphological transitions in PbTe/CdTe immiscible material systems

    Science.gov (United States)

    Mińkowski, Marcin; Załuska-Kotur, Magdalena A.; Turski, Łukasz A.; Karczewski, Grzegorz

    2016-09-01

    The crystal growth of the immiscible PbTe/CdTe multilayer system is analyzed as an example of a self-organizing process. The immiscibility of the constituents leads to the observed morphological transformations such as an anisotropy driven formation of quantum dots and nanowires and to a phase separation at the highest temperatures. The proposed model accomplishes a bulk and surface diffusion together with an anisotropic mobility of the material components. We analyze its properties by kinetic Monte Carlo simulations and show that it is able to reproduce all of the structures observed experimentally during the process of the PbTe/CdTe growth. We show that all of the dynamical processes studied play an important role in the creation of zero-, one-, two-, and, finally, three-dimensional structures. The shape of the structures that are grown is different for relatively thick multilayers, when the bulk diffusion cooperates with the anisotropic mobility, as compared to the annealed structures for which only the isotropic bulk diffusion decides about the process. Finally, it is different again for thin multilayers when the surface diffusion is the most decisive factor. We compare our results with the experimentally grown systems and show that the proposed model explains the diversity of observed structures.

  15. Effect of “CdCl2 Treatment” on Properties of CdTe-Based Solar Cells Prepared by Physical Vapor Deposition and Close-Spaced Sublimation Methods

    Science.gov (United States)

    Hajimammadov, Rashad; Fathi, Nasser; Bayramov, Ayaz; Khrypunov, Genady; Klochko, Nataliya; Li, Tatyana

    2011-05-01

    CdTe is regarded as one of the most promising materials for fabricating CdTe/CdS thin film solar cells with efficiencies up to 16.5%. In this paper we present a comparative analysis of CdTe-based solar cells fabricated by physical vapor deposition (PVD) and close-spaced sublimation (CSS) methods. The structural properties of CdTe base layers and the output parameters of CdS/CdTe solar cells are presented, and the influence of “CdCl2-treatment” on these properties are discussed. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses were used in the studies.

  16. Characterization of CdS/CdTe and CdS/CuInSe2 thin film solar cells

    Science.gov (United States)

    Cheng, L. J.; Nguyen, T. T.; Shyu, C. M.; Basol, B. M.; Yoo, H. I.

    1984-01-01

    A study on low cost polycrystalline thin film CdS/CdTe and CdS/CuInSe2 solar cells using measurements of spectral response and capacitance-voltage-frequency relationships was performed. Because of high concentrations of localized levels in the energy gap existing in materials and at interfaces, the redistribution of charge among the levels due to illumination plays an important role in the collection of light-generated current in these cells. The results illustrate some related phenomena observed in these cells.

  17. The Study on the Properties of CdTe Buffer Layer for MBE HgCdTe Epilayer%分子束外延HgCdTe薄膜的CdTe缓冲层特性研究

    Institute of Scientific and Technical Information of China (English)

    宋立媛; 唐利斌; 李艳辉; 孔令德; 陈雪梅

    2009-01-01

    CdTe是GaAs衬底上分子束外延(MBE)HgCdTe薄膜时的缓冲层,引入缓冲层的目的是减小失配位错,CdTe缓冲层的生长直接影响到后续HgCdTe薄膜的制备质量,然而目前现有文献鲜有报道CdTe缓冲层的最佳厚度.采用X射线双晶衍射、位错腐蚀坑密度(EPD)、FT-IR和椭圆偏振光谱的方法,从CdTe缓冲层厚度对位错密度的影响入手,分析并确定了理想的CdTe缓冲层厚度.%CdTe is the buffer layer of GaAs substrate for HgCdTe eoilayer grown by MBE,The purpose for introduction of buffer laver is to decrease the mismatched dislocation,the growth of CdTe buffer layer directly affects the quality of foilowing grown HgCdTe thin film.However,up to now only few papers have reported the optimum thickness for CdTe buffer layer.By using of X-ray double ervstal diffraction,EPD,FT-IR as well as soectroscopic ellipsometry the paper has studied the effects of the thickness on EPD for CdTe buffer layer,the optimum thickness of CdTe buffer layer has been obtained.

  18. Optical transmittance properties for CdS films in CdTe-HgCdTe tandem solar cells%CdTe-HgCdTe叠层太阳电池CdS窗口层透射光谱性能研究

    Institute of Scientific and Technical Information of China (English)

    郭珉; 朱秀荣; 李贺军

    2016-01-01

    Improving the spectral transmittance of CdS window layer used in CdTe-HgCdTe tandem solar cells has a significant impact on the effective utilization of sunlight and increases the device short-circuit current density(Jsc). Herein, the average transmittance(T) and Jsc losses of as-deposited and CdCl2 annealed CdS films prepared by chemical bath deposition ( CBD ) , near space sublimation ( CSS ) and magnetron sputtering(SPUT) are studied. The results show that: in the range of 520-820 nm, the as-deposited and annealed CdS films by CBD exhibit the highest T and the lowest Jsc losses of the CdTe top cell; in the range of 820-1 150 and 520-1 150 nm, the as-deposited and annealed CdS films by SPUT exhibit the highest T and the lowest Jsc losses of the HgCdTe bottom cell and the CdTe-HgCdTe tandem solar cells. In the range of 520-820, 820-1 150 and 520-1 150 nm, the CdCl2 annealing can greatly increase T of CdS films and decrease the Jsc losses of the CdTe top cell, the HgCdTe bottom cell and the CdTe-HgCdTe tandem solar cells.%CdS窗口层光谱透射率的提高对CdTe-HgCdTe叠层太阳电池有效利用入射太阳光并增大电池的短路电流密度有重要的影响。通过研究化学水浴法、近空间升华法和磁控溅射法制备的CdS薄膜在CdCl2退火前后的光谱平均透过率和短路电流密度损失表明:在光谱区520~820 nm,化学水浴法制备的CdS薄膜在退火前后具有最高的光谱平均透过率,对应的CdTe顶电池有最小的短路电流密度损失;在光谱区820~1150和520~1150 nm,磁控溅射法制备的CdS薄膜在退火前后均具有最高的光谱平均透过率,对应的HgCdTe底电池和CdTe-HgCdTe叠层太阳电池有最小的短路电流密度损失。在光谱区520~820、820~1150和520~1150 nm,CdCl2退火可以显著增大CdS薄膜的光谱平均透过率,降低对应CdTe顶电池、HgCdTe底电池和CdTe-HgCdTe叠层电池的短路电流密度损失。

  19. Photo-assisted electrodeposition of polypyrrole back contact to CdS/CdTe solar cell structures

    Energy Technology Data Exchange (ETDEWEB)

    Jarkov, A., E-mail: aleksjarkov@gmail.com [Tallinn University of Technology, Department of Materials Science, Ehitajate tee 5, 19086 Tallinn (Estonia); Bereznev, S.; Volobujeva, O. [Tallinn University of Technology, Department of Materials Science, Ehitajate tee 5, 19086 Tallinn (Estonia); Traksmaa, R. [Tallinn University of Technology, Materials Research Center, Ehitajate tee 5, 19086 Tallinn (Estonia); Tverjanovich, A. [Saint-Petersburg State University, 198503 Saint-Petersburg, Staryj Petergof, Ulyanovskaya 5 (Russian Federation); Öpik, A.; Mellikov, E. [Tallinn University of Technology, Department of Materials Science, Ehitajate tee 5, 19086 Tallinn (Estonia)

    2013-05-01

    Glass/indium tin oxide/CdS/CdTe photovoltaic structures were prepared using the high vacuum evaporation method, followed by a typical activation procedure, which involves annealing of the structures at 415–430 °C in the presence of CdCl{sub 2} in air. The main purpose of this work was to prepare and evaluate the performance of complete CdS/CdTe solar cell structures with polypyrrole (PPy) back contact and compare it to the structures with standard, copper containing back contact. Back contact layers of PPy doped with ß-naphthalene sulfonate were deposited onto activated CdTe layers by photo-assisted electrodeposition technique in a three-electrode electrochemical cell. It was found that intensive white light illumination from a xenon lamp facilitates PPy deposition at a lower applied potential range and improves quality of obtained polymer films. Applied technique gives the possibility to deposit the PPy layer strictly onto illuminated photoactive CdTe surface eliminating possible short-circuiting through pinholes and cracks in CdTe photoabsorber layer. Furthermore, relatively low deposition potential values give the possibility to reduce electrochemical degradation of CdS/CdTe photovoltaic structure in an electrochemical cell. - Highlights: ► Polypyrrole (PPy) conductive polymer back contact (BC) to CdTe semiconductor. ► Hybrid organic/inorganic photovoltaic structures. ► PPy layer to CdTe by photo-assisted electrodeposition technique ► Comparable efficiency of cells with PPy and conventional inorganic Cu{sub x}Te BC.

  20. Influence of Illumination on the Electrical Properties of p-(ZnMgTe/ZnTe:N)/CdTe/n-(CdTe:I)/GaAs Heterojunction Grown by Molecular Beam Epitaxy (MBE)

    Science.gov (United States)

    Jum'h, I.; Abd El-Sadek, M. S.; Al-Taani, H.; Yahia, I. S.; Karczewski, G.

    2017-02-01

    Heterostructure p-(ZnMgTe/ZnTe:N)/CdTe/n-(CdTe:I)/GaAs was evaporated using molecular beam epitaxy and investigated for photovoltaic energy conversion application. The electrical properties of the studied heterostructure were measured and characterized in order to understand the relevant electrical transport mechanisms. Electrical properties derived from the current-voltage ( I- V) characteristics of solar cells provide essential information necessary for the analysis of performance losses and device efficiency. I- V characteristics are investigated in dark conditions and under different light intensities. All the electrical and power parameters of the heterostructure were measured, calculated and explained.

  1. Influence of Illumination on the Electrical Properties of p-(ZnMgTe/ZnTe:N)/CdTe/n-(CdTe:I)/GaAs Heterojunction Grown by Molecular Beam Epitaxy (MBE)

    Science.gov (United States)

    Jum'h, I.; Abd El-Sadek, M. S.; Al-Taani, H.; Yahia, I. S.; Karczewski, G.

    2016-11-01

    Heterostructure p-(ZnMgTe/ZnTe:N)/CdTe/n-(CdTe:I)/GaAs was evaporated using molecular beam epitaxy and investigated for photovoltaic energy conversion application. The electrical properties of the studied heterostructure were measured and characterized in order to understand the relevant electrical transport mechanisms. Electrical properties derived from the current-voltage (I-V) characteristics of solar cells provide essential information necessary for the analysis of performance losses and device efficiency. I-V characteristics are investigated in dark conditions and under different light intensities. All the electrical and power parameters of the heterostructure were measured, calculated and explained.

  2. Specific Heat and Electrical Transport Properties of Sn0.8Ag0.2Te Superconductor

    Science.gov (United States)

    Mizuguchi, Yoshikazu; Yamada, Akira; Higashinaka, Ryuji; Matsuda, Tatsuma D.; Aoki, Yuji; Miura, Osuke; Nagao, Masanori

    2016-10-01

    Sn0.8Ag0.2Te is a new superconductor with Tc ˜ 2.4 K. The superconducting properties of Sn0.8Ag0.2Te have been investigated by specific heat measurements under magnetic fields. The bulk nature of superconductivity was confirmed from the amplitude of the specific heat jump at the superconducting transition, and the amplitude is consistent with fully gapped superconductivity. The upper critical field was estimated from specific heat and electrical resistivity measurements under magnetic fields. The Hall coefficient was positive, suggesting that Ag acts as a p-type dopant in Sn0.8Ag0.2Te.

  3. Growth of epitaxial CdTe/CdS heterostructures for single crystal thin film solar cell applications

    Energy Technology Data Exchange (ETDEWEB)

    Kessler, K.; Tiwari, A.N.; Blunier, S.; Zogg, H. [Swiss Federal Inst. of Tech., Zuerich (Switzerland). Arbeitsgemeinschaft fuer Industrielle Forschung

    1994-12-31

    Epitaxial CdTe/CdS heterostructures have been grown by molecular beam epitaxy onto BaF{sub 2} covered Si (111) substrates. An epitaxial BaF{sub 2} buffer is used for compatibility reasons, and because of easier dissolution during the lift-off processing. Epitaxy of cubic CdS (111) layers on BaF{sub 2}/Si (111) is achieved; electron channeling patterns exhibit a three-fold symmetry which is a characteristic for cubic crystal structures. The growth kinetics and structural properties of epitaxial CdS and CdTe/CdS have been studied with reflection high energy electron diffraction, Rutherford backscattering spectrometry and X-ray diffraction rocking curve measurements.the full width at half maximum of the (222) CdS and (333) CdTe X-ray peaks are {approximately} 1,150 arc sec for 2.7 and 3.4 {micro}m thick CdS and CdTe layers, respectively. To fabricate CdTe/CdS single crystal thin film solar cells, a lift-off process has been developed to remove the epitaxial layers from the Si substrates.

  4. Cu-doped CdS and its application in CdTe thin film solar cell

    Directory of Open Access Journals (Sweden)

    Yi Deng

    2016-01-01

    Full Text Available Cu is widely used in the back contact formation of CdTe thin film solar cells. However, Cu is easily to diffuse from the back contact into the CdTe absorber layer and even to the cell junction interface CdS/CdTe. This phenomenon is generally believed to be the main factor affecting the CdTe solar cell stability. In this study Cu was intentionally doped in CdS thin film to study its effect on the microstructural, optical and electrical properties of the CdS material. Upon Cu doping, the VCd− and the surface-state-related photoluminescence emissions were dramatically decreased/quenched. The presence of Cu atom hindered the recrystallization/coalescence of the nano-sized grains in the as-deposited CdS film during the air and the CdCl2 annealing. CdTe thin film solar cell fabricated with Cu-doped CdS window layers demonstrated much decreased fill factor, which was induced by the increased space-charge recombination near the p-n junction and the worsened junction crystalline quality. Temperature dependent current-voltage curve measurement indicated that the doped Cu in the CdS window layer was not stable at both room and higher temperatures.

  5. Cu-doped CdS and its application in CdTe thin film solar cell

    Science.gov (United States)

    Deng, Yi; Yang, Jun; Yang, Ruilong; Shen, Kai; Wang, Dezhao; Wang, Deliang

    2016-01-01

    Cu is widely used in the back contact formation of CdTe thin film solar cells. However, Cu is easily to diffuse from the back contact into the CdTe absorber layer and even to the cell junction interface CdS/CdTe. This phenomenon is generally believed to be the main factor affecting the CdTe solar cell stability. In this study Cu was intentionally doped in CdS thin film to study its effect on the microstructural, optical and electrical properties of the CdS material. Upon Cu doping, the VCd- and the surface-state-related photoluminescence emissions were dramatically decreased/quenched. The presence of Cu atom hindered the recrystallization/coalescence of the nano-sized grains in the as-deposited CdS film during the air and the CdCl2 annealing. CdTe thin film solar cell fabricated with Cu-doped CdS window layers demonstrated much decreased fill factor, which was induced by the increased space-charge recombination near the p-n junction and the worsened junction crystalline quality. Temperature dependent current-voltage curve measurement indicated that the doped Cu in the CdS window layer was not stable at both room and higher temperatures.

  6. Modelling of degradation/recovery phenomena in CdS/CdTe ultrathin film solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Gorji, Nima E. [University of Bologna, Department of Electrical, Electronic, and Information Engineering, Bologna (Italy)

    2015-04-01

    The degradation/recovery phenomena in ultrathin film solar cells based on CdS/CdTe are theoretically analysed using Sah-Noyce-Shockley theory for generation and recombination in the depletion region. This theory can explain the overlap of the depletion regions at both front and back contacts where the carrier generation and collection are as important as recombination mechanism. The value of physical parameters such as uncompensated defect density, carrier recombination lifetime and band bending at interface are critically important when reducing the thickness of CdTe layer down to sub-micron. The rollover, materials inter-/out-diffusion, complex defect formation and the role of mobile ions are taken into consideration to obtain an insight into the physics of degradation/recovery phenomena in ultrathin CdTe film solar cells. Both mechanisms are precisely analysed drawing the schematics of the energy band diagrams and mobile ions transport paths which in this case is the grain interior. This means that we neglect the metal diffusion through the grain boundaries which are assumed to be completely passivated. This assumption enabled us to study the role of the defects on the carrier transport in the interiors rather than through the boundaries. (orig.)

  7. Conductive Atomic Force Microscopy Applied to CdTe/CdS Solar Cells

    Energy Technology Data Exchange (ETDEWEB)

    Moutinho, H. R.; Dhere, R. G.; Jiang, C. -S.; Al-Jassim, M. M.; Kazmerski, L. L.

    2004-08-01

    In this work we describe for the first time the use of conductive atomic force microscopy (C-AFM) in the study of CdTe/CdS solar cells, before and after the etching processes used in device fabrication. C-AFM is a new technique that provides information on the electrical properties of the sample in conjunction with topographic images with high lateral resolution. At the same time, this technique allows for the generation of I-V curves at very well-defined locations. A potential is applied between the sample and a very sharp tip, which scans the sample in contact mode. The current images showed that different CdTe grains produce different contrast. Etching the CdTe with a bromine/methanol solution enhanced the current along grains boundaries when compared to the intragrain material. Etching with a solution of nitric and phosphoric acids did not show this effect. Instead, it increased the current through the whole sample surface.

  8. Facile synthesis and photoluminescence of near-infrared-emitting CdTe(x)Se(1-x) and CdTe(x)Se(1-x)/Cd(y)Zn(-1-y)S quantum dots.

    Science.gov (United States)

    Zhang, Ruili; Wang, Jianrong; Yang, Ping

    2014-03-01

    High-quality colloidal photoluminescent (PL) CdTe(x)Se(1-x) quantum dots (QDs) with gradient distribution of components, consisting of Te-rich inner cores and Se-rich outer shells, were synthesized via a facile organic method using stearic acid as a capping agent. The transmission electron microscopy observation and X-ray diffraction analysis indicated that the CdTe(x)Se(1-x) QDs revealed a "dot" shaped morphology and exhibited a zinc-blende structure which located between those of bulk CdTe and CdSe (with the lattice parameters between those of bulk CdTe and CdSe). The ternary CdTe(x)Se(1-x) QDs were emitting in the red to near-infrared (NIR) range. In order to enhance the PL properties and reduce the sensitivity to oxidation of CdTe-based QDs, the CdTe(x)Se(1-x) QDs were coated with Cd(y)Zn(1-y)S multishells by using different growth kinetics of CdS and ZnS. The coated QDs exhibited a controlled red shift of PL compared with the initial CdTe(x)Se(1-x) cores and revealed much improved PL intensity. Because of thier tunable emission from red to NIR, these composite QDs open new possibilities in band gap engineering and in developing NIR fluorescent probes for biological imaging and detection.

  9. Electronic spectrum of non-tetrahedral acceptors in CdTe:Cl and CdTe:Bi,Cl single crystals

    Energy Technology Data Exchange (ETDEWEB)

    Krivobok, V. S., E-mail: krivobok@lebedev.ru [P.N. Lebedev Physical Institute, Russian Academy of Sciences, Moscow (Russian Federation); Moscow Institute of Physics and Technology (State University), Dolgoprudny, Moscow Region (Russian Federation); Nikolaev, S. N.; Bagaev, V. S.; Pruchkina, A. A.; Onishchenko, E. E.; Kolosov, S. A.; Klevkov, Yu. V.; Skorikov, M. L. [P.N. Lebedev Physical Institute, Russian Academy of Sciences, Moscow (Russian Federation)

    2016-02-07

    The electronic spectra of complex acceptors in compensated CdTe:Cl, CdTe:Ag,Cl, and CdTe:Bi,Cl single crystals are studied using low-temperature photoluminescence (PL) measurements under both nonresonant and resonant excitation of distant donor–acceptor pairs (DAP). The wavelength modulation of the excitation source combined with the analysis of the differential PL signal is used to enhance narrow spectral features obscured because of inhomogeneous line broadening and/or excitation transfer for selectively excited DAPs. For the well-known tetrahedral (T{sub D}) Ag{sub Cd} acceptor, the energies of four excited states are measured, and the values obtained are shown to be in perfect agreement with the previous data. Moreover, splitting between the 2P{sub 3/2} (Γ{sub 8}) and 2S{sub 3/2} (Γ{sub 8}) states is clearly observed for Ag{sub Cd} centers located at a short distance (5–7 nm) from a hydrogen-like donor (Cl{sub Te}). This splitting results from the reduction of the T{sub D} symmetry taking place when the acceptor is a member of a donor–acceptor pair. For the Cl-related complex acceptor with an activation energy of ∼121 meV (A-center), the energies of eight excited states are measured. It is shown that this defect produces low-symmetry central-cell correction responsible for the strong splitting of S-like T{sub D} shells. The energy spectrum of the Bi-related shallow acceptor with an activation energy of ∼36 meV is measured as well. The spectrum obtained differs drastically from the hydrogen-like set of levels, which indicates the existence of repulsive low-symmetry perturbation of the hydrogen-like Coulomb potential. It is also shown that the spectra of selectively excited PL recorded for a macroscopic ensemble of distant donor–acceptor pairs allow one to detect the low symmetry of acceptors of a given type caused by their complex nature or by the Jahn–Teller distortion. This method does not require any additional (external) field and is

  10. High-Efficiency, Commercial Ready CdTe Solar Cells

    Energy Technology Data Exchange (ETDEWEB)

    Sites, James R. [Colorado State Univ., Fort Collins, CO (United States)

    2015-11-19

    Colorado State’s F-PACE project explored several ways to increase the efficiency of CdTe solar cells and to better understand the device physics of those cells under study. Increases in voltage, current, and fill factor resulted in efficiencies above 17%. The three project tasks and additional studies are described in detail in the final report. Most cells studied were fabricated at Colorado State using an industry-compatible single-vacuum closed-space-sublimation (CSS) chamber for deposition of the key semiconductor layers. Additionally, some cells were supplied by First Solar for comparison purposes, and a small number of modules were supplied by Abound Solar.

  11. Study of a new architecture of gamma cameras with Cd/ZnTe/CdTe semiconductors; Etude d'une nouvelle architecture de gamma camera a base de semi-conducteurs CdZnTe /CdTe

    Energy Technology Data Exchange (ETDEWEB)

    Guerin, L

    2007-11-15

    This thesis studies new semi conductors for gammas cameras in order to improve the quality of image in nuclear medicine. The chapter 1 reminds the general principle of the imaging gamma, by describing the radiotracers, the channel of detection and the types of Anger gamma cameras acquisition. The physiological, physical and technological limits of the camera are then highlighted, to better identify the needs of future gamma cameras. The chapter 2 is dedicated to a bibliographical study. At first, semi-conductors used in imaging gamma are presented, and more particularly semi-conductors CDTE and CdZnTe, by distinguishing planar detectors and monolithic pixelated detectors. Secondly, the classic collimators of the gamma cameras, used in clinical routine for the most part of between them, are described. Their geometry is presented, as well as their characteristics, their advantages and their inconveniences. The chapter 3 is dedicated to a state of art of the simulation codes dedicated to the medical imaging and the methods of reconstruction in imaging gamma. These states of art allow to introduce the software of simulation and the methods of reconstruction used within the framework of this thesis. The chapter 4 presents the new architecture of gamma camera proposed during this work of thesis. It is structured in three parts. The first part justifies the use of semiconducting detectors CdZnTe, in particular the monolithic pixelated detectors, by bringing to light their advantages with regard to the detection modules based on scintillator. The second part presents gamma cameras to base of detectors CdZnTe (prototypes or commercial products) and their associated collimators, as well as the interest of an association of detectors CdZnTe in the classic collimators. Finally, the third part presents in detail the HiSens architecture. The chapter 5 describes both software of simulation used within the framework of this thesis to estimate the performances of the Hi

  12. Characteristics of a prototype CdZnTe detector

    Institute of Scientific and Technical Information of China (English)

    XU Huichao; CHENG Cheng; ZHAO Cuilan; ZHANG Jinzhou; PU Shijie

    2007-01-01

    Cadmium zinc telluride(CZT)is a preferred material for X-ray and gamma-ray detector.Thanks to the relatively high atomic number,high density and wide band-gap.CZT detector possesses sharp energy resolution and high detection efficiency without cryogenic cooling.We have developed a CdZnTe detector with an energy resolution of 3.45%(FWHM)at 59.54 keV at room temperature.and it is used for X-ray fluorescence analysis.In this paper,leakage current,energy resolution and long term stability of the CZT detector are discussed.

  13. The strange diffusivity of Ag atoms in CdTe

    CERN Document Server

    Wolf, H; Ostheimer, V; Schachtrup, A R; Stolwijk, N A; Wichert, T

    2001-01-01

    The diffusion of Ag atoms in CdTe was investigated using the radiotracer $^{111}\\!$Ag, which was introduced by implantation with an energy of 60 or 80 keV. The measured diffusion profiles are explained by assuming the existence of a repulsive interaction between Ag and residual Cu atoms causing a drift of the Ag atoms towards the centre of the crystal, which supposes the diffusion in a concentration gradient. This effect vanishes if the Ag concentration is increased and becomes more pronounced if the crystals are simultaneously co- doped with Cu. (11 refs).

  14. Characterization of CdTe Films Deposited at Various Bath Temperatures and Concentrations Using Electrophoretic Deposition

    Directory of Open Access Journals (Sweden)

    Zulkarnain Zainal

    2012-05-01

    Full Text Available CdTe film was deposited using the electrophoretic deposition technique onto an ITO glass at various bath temperatures. Four batch film compositions were used by mixing 1 to 4 wt% concentration of CdTe powder with 10 mL of a solution of methanol and toluene. X-ray Diffraction analysis showed that the films exhibited polycrystalline nature of zinc-blende structure with the (111 orientation as the most prominent peak. From the Atomic Force Microscopy, the thickness and surface roughness of the CdTe film increased with the increase of CdTe concentration. The optical energy band gap of film decreased with the increase of CdTe concentration, and with the increase of isothermal bath temperature. The film thickness increased with respect to the increase of CdTe concentration and bath temperature, and following, the numerical expression for the film thickness with respect to these two variables has been established.

  15. Characterization of CdTe films deposited at various bath temperatures and concentrations using electrophoretic deposition.

    Science.gov (United States)

    Daud, Mohd Norizam Md; Zakaria, Azmi; Jafari, Atefeh; Ghazali, Mohd Sabri Mohd; Abdullah, Wan Rafizah Wan; Zainal, Zulkarnain

    2012-01-01

    CdTe film was deposited using the electrophoretic deposition technique onto an ITO glass at various bath temperatures. Four batch film compositions were used by mixing 1 to 4 wt% concentration of CdTe powder with 10 mL of a solution of methanol and toluene. X-ray Diffraction analysis showed that the films exhibited polycrystalline nature of zinc-blende structure with the (111) orientation as the most prominent peak. From the Atomic Force Microscopy, the thickness and surface roughness of the CdTe film increased with the increase of CdTe concentration. The optical energy band gap of film decreased with the increase of CdTe concentration, and with the increase of isothermal bath temperature. The film thickness increased with respect to the increase of CdTe concentration and bath temperature, and following, the numerical expression for the film thickness with respect to these two variables has been established.

  16. CdTe microwire-based ultraviolet photodetectors aligned by a non-uniform electric field

    Science.gov (United States)

    Park, Hyunik; Yang, Gwangseok; Chun, Seungju; Kim, Donghwan; Kim, Jihyun

    2013-07-01

    We report on ultraviolet (UV) photodetectors fabricated by positioning Cadmium Telluride (CdTe) microwires (μWs) precisely by dielectrophoretic (DEP) force, where CdTe μWs were grown using an Au-catalyst-assisted closed-space-sublimation (CSS) method. The optical properties of CSS-grown CdTe μWs were characterized by micro-photoluminescence and micro-Raman spectroscopies. Optoelectronic characteristics were obtained after CdTe μWs were aligned on a pre-patterned SiO2/Si substrate by a non-uniform electric field. Photocurrents were increased with increasing the light intensities. Fast and reliable photoresponse and recovery were observed when CdTe μWs were exposed to UV illuminations. We demonstrated that high quality CdTe μWs grown by the CSS method have significant potentials as optoelectronic devices.

  17. Influence of Deposition Conditions on Properties of All Sputtered CdS/CdTe Thin-Film Solar Cells.

    Science.gov (United States)

    Kim, Minha; Kim, Doyoung; Shim, Joong-Pyo; Kim, Donguk; Lee, Jaehyeong

    2016-05-01

    The effects of deposition conditions, such as substrate temperature and CdCl2 post treatments, on the structural and optical properties of CdTe films were investigated. In addition, CdS/CdTe thin-film solar cells were fabricated by an all-sputtering process, and their photovoltaic characteristics were studied. The CdTe films had a polycrystalline, cubic structure with a preferred orientation of the [1 1 1] direction parallel to the substrate surface, regardless of the substrate temperature. As the substrate temperature increased, the crystallinity of CdTe films improved. The grain size of the CdTe films increased after CdCl2 post treatment. In addition, the optical band gap increased with the substrate temperature. The conversion efficiency of the CdS/CdTe solar cell improved at higher substrate temperatures. The maximum efficiency, 9.23%, was obtained at a substrate temperature of 400 degrees C, with an open-circuit voltage (V(oc)) of 0.78 V, a short-circuit current density (J(sc)) of 20.4 mA/cm2, and a fill factor of 0.58.

  18. Enhanced Thermoelectric Properties of Sn0.8Pb0.2Te Alloy by Mn Substitution

    Science.gov (United States)

    Li, J. Q.; Lu, Z. W.; Wang, C. Y.; Li, Y.; Liu, F. S.; Ao, W. Q.

    2016-06-01

    A series of (Sn0.8Pb0.2)1- x Mn x Te alloys with x = 0, 0.03, 0.06, 0.09, 0.12 and 0.15 were prepared by melting, quenching and spark plasma sintering (SPS) techniques to investigate their phases and thermoelectric properties. Mn was used as doped element in Sn0.8Pb0.2Te solid solution to reduce the carrier concentration, enhance the Seebeck coefficient and reduce the thermal conductivity of the material. Experimental results show that the SnTe-based solid solution single phase was formed in the alloys with x = 0 and 0.03. The minor irregular-shaped MnTe2 phase presents in the alloys with x ≥ 0.06, while the minor needle-like MnTe phase appears in the alloys with x ≥ 0.12, together with the SnTe-based solid solution matrix. The lattice parameter a of SnTe-based solid solution decreases nearly linearly as Mn content x increases up to 0.12, but keeps constant as x further increases. All the samples show p-type conduction. Mn doping in Sn0.8Pb0.2Te decreases its carrier concentration and thus increases its Seebeck coefficient. The solute Mn and Pb atoms in the SnTe-based solid solution, and the minor phases MnTe2 and MnTe, enhance the phonon scattering and thus reduce the thermal conductivity. As a result, the figure-of-merit ZT of the (Sn0.8Pb0.2)1- x Mn x Te composites can be enhanced with proper Mn substitution. The maximum ZT of 0.65 was obtained in the sample (Sn0.8Pb0.2)0.88Mn0.12Te at 723 K, which is higher than the 0.29 of its parent alloy Sn0.8Pb0.2Te.

  19. Electrochemical synthesis of CdTe/SWNT hybrid nanostructures and their tunable electrical and optoelectrical properties.

    Science.gov (United States)

    Chang, Chong Hyun; Jung, Hyunsung; Rheem, Youngwoo; Lee, Kyu-Hwan; Lim, Dong-Chan; Jeong, Yongsoo; Lim, Jae-Hong; Myung, Nosang V

    2013-02-21

    A facile electrodeposition technique was utilized to deposit single-walled carbon nanotubes (SWNTs) with cadmium telluride (CdTe) with well-controlled size, density, surface morphology, and composition. By controlling the applied charge, the morphology of these hybrid nanostructures was altered from CdTe nanoparticles on SWNTs to SWNT/CdTe core/shell nanostructures and the composition of the CdTe nanoparticles was altered from Te-rich (29 at% Cd) to Cd-rich (79 at% Cd) CdTe by adjusting the deposition potential. The electrical and optoelectrical properties of these hybrid nanostructures showed that photo-induced current can be tuned by tailoring the conductivity type (n-type or p-type), morphology, and size of the CdTe nanostructures, with a maximum photosensitivity (ΔI/I(0)) of about 30% for SWNT/Cd-rich CdTe (n-type) core/shell nanostructures. This work demonstrates a novel approach for synthesizing metal chalcogenide/SWNT hybrid nanostructures for various electrical and optoelectrical applications.

  20. Comparative study of trap densities of states in CdTe /CdS solar cells

    Science.gov (United States)

    Proskuryakov, Y. Y.; Major, J. D.; Durose, K.; Barrioz, V.; Irvine, S. J. C.; Jones, E. W.; Lamb, D.

    2007-10-01

    Density of deep and shallow states has been investigated in three different kinds of CdTe /CdS samples, two of which were grown by metal-organic chemical vapor deposition (MOCVD) and one by close-space sublimation (CSS) methods. The MOCVD samples were p doped by As and grown either with or without a ZnO buffer layer between the transparent conductor and CdS layers. Capacitance-voltage, admittance spectroscopy, and quantum efficiency measurements show pronounced effects of As doping and ZnO incorporation. It is found that A centers and vacancies of Cd, usually observed in CSS devices, are absent in the defect spectra of MOCVD samples.

  1. Sputtered CdTe thin film solar cells with Cu{sub 2}Te/Au back contact

    Energy Technology Data Exchange (ETDEWEB)

    Park, Yongseob [Department of Photoelectronics Information, Chosun College of Science and Technology, Pilmudaero 309-1, Dong-gu, Gwangju 501-744 (Korea, Republic of); Lee, Suho; Yi, Junsin; Choi, Byung-Duck [School of Electronic and Electrical Engineering, Sungkyunkwan University, Cheoncheon-dong 300, Jangan-gu, Suwon 440-746 (Korea, Republic of); Kim, Doyoung [School of Electricity and Electronics, Ulsan College, Daehak-ro 57, Nam-gu, Ulsan 680-749 (Korea, Republic of); Lee, Jaehyeong, E-mail: jaehyeong@skku.edu [School of Electronic and Electrical Engineering, Sungkyunkwan University, Cheoncheon-dong 300, Jangan-gu, Suwon 440-746 (Korea, Republic of)

    2013-11-01

    In this work, Cu{sub 2}Te/Au back contact for CdTe thin film solar cells were prepared by vacuum evaporation. Influence of annealing temperature on the structure and electrical properties of Cu{sub 2}Te films were investigated by field emission scanning electron microscope, X-ray diffraction, and Hall effect measurement. Also, CdS/CdTe thin film solar cells were fabricated by magnetron sputtering process, which is favorable for large area deposition and mass production, and the photovoltaic characteristics were studied. As the annealing temperature was increased, the crystal structure transformed from Cu{sub 2}Te for as-deposited film to Cu{sub 2−x}Te hexagonal phase, and the grains in the film became bigger. The electrical resistivity was slightly higher by the annealing. The cell efficiency was significantly improved by the heat treatment, and showed a maximum value of 9.14% at 180 °C. From these results, Cu{sub 2}Te/Au contact acts as the proper pseudo-ohmic contact onto CdTe film. However, further increase of annealing temperature caused the deterioration of cell performance. - Highlights: • Annealing effects of the vacuum evaporated Cu{sub 2}Te films were investigated. • The transformation from Cu{sub 2}Te to Cu{sub 2−x}Te hexagonal phase occurred by annealing. • The performance of the solar cell was highly increased by annealing at 180 °C. • Cu{sub 2}Te/Au contact acts as the proper pseudo-ohmic contact onto CdTe film.

  2. High Efficiency Single Crystal CdTe Solar Cells: November 19, 2009 - January 31, 2011

    Energy Technology Data Exchange (ETDEWEB)

    Carmody, M.; Gilmore, A.

    2011-05-01

    The goal of the program was to develop single crystal CdTe-based top cells grown on Si solar cells as a platform for the subsequent manufacture of high efficiency tandem cells for CPV applications. The keys to both the single junction and the tandem junction cell architectures are the ability to grow high quality single-crystal CdTe and CdZnTe layers on p-type Si substrates, to dope the CdTe and CdZnTe controllably, both n and p-type, and to make low resistance ohmic front and back contacts. EPIR demonstrated the consistent MBE growth of CdTe/Si and CdZnTe/Si having high crystalline quality despite very large lattice mismatches; epitaxial CdTe/Si and CdZnTe/Si consistently showed state-of-the-art electron mobilities and good hole mobilities; bulk minority carrier recombination lifetimes of unintentionally p-doped CdTe and CdZnTe grown by MBE on Si were demonstrated to be consistently of order 100 ns or longer; desired n- and p-doping levels were achieved; solar cell series specific resistances <10 ?-cm2 were achieved; A single-junction solar cell having a state-of-the-art value of Voc and a unverified 16.4% efficiency was fabricated from CdZnTe having a 1.80 eV bandgap, ideal for the top junction in a tandem cell with a Si bottom junction.

  3. Characterization of Cr(V)-induced genotoxicity using CdTe nanocrystals as fluorescent probes.

    Science.gov (United States)

    Zhang, Wen-Hao; Sui, Chao-Xia; Wang, Xie; Yin, Gong-Ju; Liu, Ying-Fan; Zhang, Ding

    2014-12-21

    CdTe nanocrystals capped by cysteamine were synthesized to study Cr(V)-induced genotoxicity. On the surface of TiO2 thin films, the stepwise process of DNA breakage induced by Cr(V)-GSH complexes was vividly observed by using CdTe-DNA self-assembled fluorescent probes; in acetate buffer solution, an analytical method was developed to detect Cr(V)-induced genotoxicity with CdTe fluorescent probes.

  4. Luminescence effects of ion-beam bombardment of CdTe surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Olvera, J., E-mail: javier.olvera@uam.e [Laboratorio de Crecimiento de Cristales, Dpto. de Fisica de Materiales, Facultad de Ciencias, Universidad Autonoma de Madrid, Cantoblanco, 28049 Madrid (Spain); Martinez, O. [Optronlab Group, Dpto. Fisica Materia Condensada, Edificio I-D, Universidad de Valladolid, Paseo de Belen 1, 47011 Valladolid (Spain); Plaza, J.L.; Dieguez, E. [Laboratorio de Crecimiento de Cristales, Dpto. de Fisica de Materiales, Facultad de Ciencias, Universidad Autonoma de Madrid, Cantoblanco, 28049 Madrid (Spain)

    2009-09-15

    In the present work, we report the effect of low-energy ion bombardment on CdTe surfaces. The effect is revealed by FESEM images and photoluminescence (PL) measurements carried out before and after irradiation of CdTe polycrystals by means of an ion-beam sputtering (IBS) system. An important improvement in the luminescence of CdTe was observed in the irradiated areas, related to defect-free surfaces.

  5. Plasma kinetics and biodistribution of water-soluble CdTe quantum dots in mice: a comparison between Cd and Te

    Science.gov (United States)

    Han, Ying; Xie, Guangyun; Sun, Zhiwei; Mu, Ying; Han, Sihai; Xiao, Yang; Liu, Na; Wang, Hui; Guo, Caixia; Shi, Zhixiong; Li, Yanbo; Huang, Peili

    2011-10-01

    Water-soluble quantum dots (QDs) have shown potential as tumor diagnostic agents. However, little is known about their biological behaviors in vivo. Male ICR mice were intravenously given a single dose (2.5 μmol kg-1 body weight) of water-soluble cadmium-telluride (CdTe) QDs (the QDs are approximately 4 nm in diameter and have maximal emission at 630 nm). Inductively coupled plasma mass spectrometry (ICP-MS) was used for measuring the kinetic action of 111Cd and 125Te for 7 days. The plasma kinetics of Cd and Te followed a two-compartment model, in which Cd exhibited greater apparent volume of distribution, greater clearance, faster distribution half-life, and significantly slower elimination half-life compared to Te. Contrary to its relatively transient fate in the plasma, high levels of Cd persisted in the liver and kidneys. Te accumulated primarily in the spleen. The different plasma kinetics and distribution patterns of Cd and Te imply that CdTe QDs have been part of the degradation or aggregation in vivo.

  6. Ge2Sb2Te5/SnSe2 nanocomposite multilayer thin films for phase change memory application

    Science.gov (United States)

    Feng, Xiaoyi; Wen, Ting; Zhai, Jiwei; Lai, Tianshu; Wang, Changzhou; Song, Sannian; Song, Zhitang

    2014-10-01

    By nanocompositing Ge2Sb2Te5 and SnSe2, the electrical and thermal proprieties of Ge2Sb2Te5/SnSe2 multilayer films for phase change random access memory (PCRAM) are better than those of Ge2Sb2Te5 films. The crystallization temperature rises and can be controlled. The resistance gap can reach approximately five orders of magnitude to ensure high data reliability. The activity energy (Ea) is more than 2.60 eV and the temperature for 10 year data retention reach 110 °C. The analysis of both XRD patterns and TEM images confirmed the reversible phase change transition between amorphous and crystalline state in Ge2Sb2Te5/SnSe2 nanocomposite multilayer films. According to transient photoreflectance traces, the speed of crystallization process was about 33 ns. Among different Ge2Sb2Te5/SnSe2 multilayer films, the film constitute of [Ge2Sb2Te5 (4 nm)/SnSe2(10 nm)]7 showed better properties and was manufactured by CMOS technology to phase change memory (PCM) cells. This result revealed that the Ge2Sb2Te5/SnSe2 nanocomposite multilayer film is a promising phase change material.

  7. Recombination by grain-boundary type in CdTe

    Energy Technology Data Exchange (ETDEWEB)

    Moseley, John, E-mail: john.moseley@nrel.gov; Ahrenkiel, Richard K. [National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, Colorado 80401 (United States); Colorado School of Mines, 1500 Illinois Street, Golden, Colorado 80401 (United States); Metzger, Wyatt K.; Moutinho, Helio R.; Guthrey, Harvey L.; Al-Jassim, Mowafak M. [National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, Colorado 80401 (United States); Paudel, Naba; Yan, Yanfa [Department of Physics & Astronomy, University of Toledo, Toledo, Ohio 43606 (United States)

    2015-07-14

    We conducted cathodoluminescence (CL) spectrum imaging and electron backscatter diffraction on the same microscopic areas of CdTe thin films to correlate grain-boundary (GB) recombination by GB “type.” We examined misorientation-based GB types, including coincident site lattice (CSL) Σ = 3, other-CSL (Σ = 5–49), and general GBs (Σ > 49), which make up ∼47%–48%, ∼6%–8%, and ∼44%–47%, respectively, of the GB length at the film back surfaces. Statistically averaged CL total intensities were calculated for each GB type from sample sizes of ≥97 GBs per type and were compared to the average grain-interior CL intensity. We find that only ∼16%–18% of Σ = 3 GBs are active non-radiative recombination centers. In contrast, all other-CSL and general GBs are observed to be strong non-radiative centers and, interestingly, these GB types have about the same CL intensity. Both as-deposited and CdCl{sub 2}-treated films were studied. The CdCl{sub 2} treatment reduces non-radiative recombination at both other-CSL and general GBs, but GBs are still recombination centers after the CdCl{sub 2} treatment.

  8. 3D Lifetime Tomography Reveals How CdCl 2 Improves Recombination Throughout CdTe Solar Cells

    Energy Technology Data Exchange (ETDEWEB)

    Barnard, Edward S. [Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley CA 94720 USA; PLANT PV, Inc, Alameda CA 94501 USA; Ursprung, Benedikt [PLANT PV, Inc, Alameda CA 94501 USA; Colegrove, Eric [National Renewable Energy Laboratory, Golden CO 80401 USA; Moutinho, Helio R. [National Renewable Energy Laboratory, Golden CO 80401 USA; Borys, Nicholas J. [Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley CA 94720 USA; Hardin, Brian E. [PLANT PV, Inc, Alameda CA 94501 USA; Peters, Craig H. [PLANT PV, Inc, Alameda CA 94501 USA; Metzger, Wyatt K. [National Renewable Energy Laboratory, Golden CO 80401 USA; Schuck, P. James [Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley CA 94720 USA

    2016-11-15

    Using two-photon tomography, carrier lifetimes are mapped in polycrystalline CdTe photovoltaic devices. These 3D maps probe subsurface carrier dynamics that are inaccessible with traditional optical techniques. They reveal that CdCl2 treatment of CdTe solar cells suppresses nonradiative recombination and enhances carrier lifetimes throughout the film with substantial improvements particularly near subsurface grain boundaries and the critical buried p-n junction.

  9. Investigation of Junction Properties in CdS/CdTe Solar Cells and Their Correlation to Device Properties: Preprint

    Energy Technology Data Exchange (ETDEWEB)

    Dhere, R. G.; Zhang, Y.; Romero, M. J.; Asher, S. E.; Young, M.; To, B.; Noufi, R.; Gessert, T. A.

    2008-05-01

    Secondary-ion mass spectrometry analysis of the CdS/CdTe interface shows that S diffusion in CdTe increases with substrate temperature and CdCl2 heat treatment. There is also an accumulation of Cl at the interface for CdCl2-treated samples. Modulated photo-reflectance studies shows that devices with CdCl2 heat treatment and open-circuit voltage (Voc) of 835 mV have a distinct high electric-field region in the layer with bandgap of 1.45 eV. Electron-beam induced current measurements reveal a one-sided junction for high Voc devices. The nature of the junction changes with processing. For heterojunction devices, the depletion region includes the highly defective CdS/CdTe interface, which would increase the recombination current and consequently the dark current, leading to lower Voc. In the case of CdCl2-treated cells, the n+-p junction and its high electric-field results in the junction between structurally compatible CdTe and the Te-rich CdSTe alloy, and thus, in higher Voc.

  10. A photoluminescence study of polycrystalline thin-film CdTe/CdS solar cells

    Science.gov (United States)

    Halliday, D. P.; Eggleston, J. M.; Durose, K.

    1998-03-01

    The structures studied here are photovoltaic cells composed of indium tin oxide (ITO) coated glass, 500 nm of CdS and 5 μm of CdTe. The devices are grown by close-space sublimation (CSS). The as-grown cells have a photovoltaic efficiency of η=0.8%. Following deposition of CdCl 2 and annealing in air at 400°C, the efficiency increases to around 10%. A study of the cells is made by examining the variation in the photoluminescence from the surface of the CdTe layer with laser power and sample temperature for an as-grown cell, an air-annealed cell and a cell which has undergone CdCl 2 treatment. Three luminescence bands are observed at 1.590, 1.555 and 1.45 eV. These are attributed to shallow donor and acceptor bound excitons, a free to bound transition and a deep-level acceptor complex. The observed emissions are analysed and correlated to the changes in the cell characteristics.

  11. Hybrid morphology dependence of CdTe:CdSe bulk-heterojunction solar cells.

    Science.gov (United States)

    Tan, Furui; Qu, Shengchun; Zhang, Weifeng; Wang, Zhanguo

    2014-01-01

    A nanocrystal thin-film solar cell operating on an exciton splitting pattern requires a highly efficient separation of electron-hole pairs and transportation of separated charges. A hybrid bulk-heterojunction (HBH) nanostructure providing a large contact area and interpenetrated charge channels is favorable to an inorganic nanocrystal solar cell with high performance. For this freshly appeared structure, here in this work, we have firstly explored the influence of hybrid morphology on the photovoltaic performance of CdTe:CdSe bulk-heterojunction solar cells with variation in CdSe nanoparticle morphology. Quantum dot (QD) or nanotetrapod (NT)-shaped CdSe nanocrystals have been employed together with CdTe NTs to construct different hybrid structures. The solar cells with the two different hybrid active layers show obvious difference in photovoltaic performance. The hybrid structure with densely packed and continuously interpenetrated two phases generates superior morphological and electrical properties for more efficient inorganic bulk-heterojunction solar cells, which could be readily realized in the NTs:QDs hybrid. This proved strategy is applicable and promising in designing other highly efficient inorganic hybrid solar cells.

  12. Core-shell ITO/ZnO/CdS/CdTe nanowire solar cells

    Science.gov (United States)

    Williams, B. L.; Taylor, A. A.; Mendis, B. G.; Phillips, L.; Bowen, L.; Major, J. D.; Durose, K.

    2014-02-01

    Radial p-n junction nanowire (NW) solar cells with high densities of CdTe NWs coated with indium tin oxide (ITO)/ZnO/CdS triple shells were grown with excellent heterointerfaces. The optical reflectance of the devices was lower than for equivalent planar films by a factor of 100. The best efficiency for the NW solar cells was η = 2.49%, with current transport being dominated by recombination, and the conversion efficiencies being limited by a back contact barrier (ϕB = 0.52 eV) and low shunt resistances (RSH < 500 Ω.cm2).

  13. Role of Copper in the Performance of CdS/CdTe Solar Cells (Poster)

    Energy Technology Data Exchange (ETDEWEB)

    Demtsu, S.; Albin, D.; Sites, J.

    2006-05-01

    The performance of CdS/CdTe solar cells made with evaporated Cu as a primary back contact was studied through current-voltage (JV) at different intensities, quantum efficiency (QE) under light and voltage bias, capacitance-voltage (CV), and drive-level capacitance profiling (DLCP) measurements. The results show that while modest amounts of Cu enhance cell performance, excessive amounts degrade device quality and reduce performance. The analysis is supported with numerical simulations to reproduce and explain some of the experimental results.

  14. Role of Copper in the Performance of CdS/CdTe Solar Cells: Preprint

    Energy Technology Data Exchange (ETDEWEB)

    Demtsu, S.; Albin, D.; Sites, J.

    2006-05-01

    The performance of CdS/CdTe solar cells made with evaporated Cu as a primary back contact was studied through current-voltage (JV) at different intensities, quantum efficiency (QE) under light and voltage bias, capacitance-voltage (CV), and drive-level capacitance profiling (DLCP) measurements. The results show that while modest amounts of Cu enhance cell performance, excessive amounts degrade device quality and reduce performance. The analysis is supported with numerical simulations to reproduce and explain some of the experimental results.

  15. Photovoltaic characteristics of CdS/CdTe screen printed heterojunction

    Energy Technology Data Exchange (ETDEWEB)

    Tomar, M.S.; Garcia, F.J.

    1984-05-01

    The screen printing technique has been used to prepare solar cells in recent years. In the present work the authors have prepared a n-CdS/p-CdTe heterojunction solar cell of simple structure using screen printing. Open circuit voltage (Voc) = 520mV and short circuit current density (J /SUB sc/ >19mA/cm/sup 2/) have been obtained. A conversion efficiency of more than 4.5% has been obtained for a cell area of 1.05cm/sup 2/.

  16. Highly fluorescent CdTe quantum dots with reduced cytotoxicity-A Robust biomarker

    Directory of Open Access Journals (Sweden)

    Jandi Kim

    2015-03-01

    Full Text Available l-Cysteine (Cys capped CdTe quantum dots (CdTe@Cys QDs were successfully synthesized in an aqueous medium. The synthesized CdTe@Cys samples were analyzed using Fourier transform infrared (FT-IR spectroscopy, fluorescence (FL spectroscopy, transmission electron microscopy (TEM, confocal microscopy and subsequently subjected to the antibacterial test. Systematic investigations were carried out for the determination of optimal conditions namely the ratios of Cd:Te, CdTe:Cys, pH value and the chemical stability of CdTe@Cys. Moreover, the reactivation of FL intensity in the CdTe@Cys sample was done easily by the addendum of Cys. The introduction of additional cysteine to the CdTe@Cys QDs sample showed an enhancement in terms of the FL intensity and stability along with the reduced antibacterial activity. This was further confirmed through Thiazolyl blue tetrazolium bromide (MTT assays. Both the result of the bio-stability tests namely the antibacterial test and MTT assay displayed similarities between the externally added Cys and cytotoxicity of the bacteria and human HeLa cancer cell lines. Confocal microscopic images were captured for the CdTe@Cys conjugated Escherichia coli.

  17. HgCdTe detector technology at Kunming Institute of Physics

    Science.gov (United States)

    Su, Junhong; Zeng, Gehong

    1996-09-01

    HgCdTe detector and thermal image system laboratories at Kunming Institute of Physics have been carrying the research and development of HgCdTe detectors and thermal imaging systems for a wide range applications for over 20 years. During this period, significant progress has been made in many areas such as HgCdTe material, detector, miniature dewar and cooler to meet the requirements of civil and military operations. This paper describes these activities and present status of HgCdTe technology at Kunming Institute of Physics, and some of the problems we faced and how they were solved.

  18. Folic acid-CdTe quantum dot conjugates and their applications for cancer cell targeting

    Energy Technology Data Exchange (ETDEWEB)

    Suriamoorthy, Preethi; Zhang, Xing; Hao, Guiyang; Joly, Alan G.; Singh, S.; Hossu, Marius; Sun, Xiankai; Chen, Wei

    2010-12-01

    In this study, we report the preparation,luminescence, and targeting properties of folic acid- CdTe quantum dot conjugates. Water-soluble CdTe quantum dots were synthesized and conjugated with folic acid using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide-N-hydroxysuccinimide chemistry. The in-fluence of folic acid on the luminescence properties of CdTe quantum dots was investigated, and no energy transfer between them was observed. To investigate the efficiency of folic acid-CdTe nanoconjugates for tumor targeting, pure CdTe quantum dots and folic acid-coated CdTe quantum dots were incubated with human naso- pharyngeal epidermal carcinoma cell line with positive expressing folic acid receptors (KB cells) and lung cancer cells without expression of folic acid receptors (A549 cells). For the cancer cells with positive folate receptors (KB cells), the uptake for CdTe quantum dots is very low, but for folic acid-CdTe nanoconjugates, the uptake is very high. For the lung cancer cells without folate receptors (A549 cells), the uptake for folic acid- CdTe nanoconjugates is also very low. The results indicate that folic acid is an effective targeting molecule for tumor cells with overexpressed folate receptors.

  19. Photoluminescence and Electroluminescence Properties of CdTe Nanoparticles in Conjugated Polymer Hosts

    Institute of Scientific and Technical Information of China (English)

    GUO, Fengqi; XIE, Puhui

    2009-01-01

    The photoinduced energy transfer process from conjugated polymer (PPE4+) to CdTe nanocrystals was found both in solutions and in thin films by a fluorescence spectroscopic technique. Films of PPE4+ blended with CdTe-2 nanocrystals were formed by an electrostatic layer-by-layer assembly technique. Light emitting diodes were fabricated using CdTe-2 as an emitter in PPE4+ host. PPE4+ works as a molecular wire in the energy transfer process from the polymer to the CdTe-2 nanocrystals.

  20. Review of Photovoltaic Energy Production Using CdTe Thin-Film Modules: Extended Abstract Preprint

    Energy Technology Data Exchange (ETDEWEB)

    Gessert, T. A.

    2008-09-01

    CdTe has near-optimum bandgap, excellent deposition traits, and leads other technologies in commercial PV module production volume. Better understanding materials properties will accelerate deployment.

  1. Preparation and characterization of ZnTe as an interlayer for CdS/CdTe substrate thin film solar cells on flexible substrates

    Energy Technology Data Exchange (ETDEWEB)

    Feng, Xianjin, E-mail: xianjinfeng@gmail.com; Singh, Kartikay; Bhavanam, Sushma; Palekis, Vasilios; Morel, Don L.; Ferekides, Chris

    2013-05-01

    ZnTe thin films have been prepared on Mo-coated stainless steel substrates by the close spaced sublimation (CSS) technique. Cu-doped ZnTe (ZnTe:Cu) films are prepared by immersing the as-deposited samples in a CuCl–H{sub 2}O solution. The structural and morphological properties of the ZnTe films as a function of substrate temperature are investigated using X-ray diffraction and scanning electron microscopy. CdS/CdTe solar cells with and without the ZnTe and ZnTe:Cu interlayers are prepared and characterized with current–voltage (J–V), spectral response, and capacitance–voltage measurements. The structural and morphological properties of the ZnTe films prepared by CSS are found to be strongly influenced by the substrate temperature. The ‘roll-over’ behavior in the J–V characteristics of the CdS/CdTe solar cells due to a Schottky barrier at the back contact can be eliminated using ZnTe as the interlayer. Preliminary results on the application of ZnTe:Cu films suggest that the open circuit voltage and fill factor can be further improved, depending on processing conditions. - Highlights: ► Thin film CdTe solar cells on flexible stainless steel substrates are prepared. ► Using ZnTe can eliminate the ‘roll-over’ behavior in the current–voltage curve. ► Incorporating Cu can further improve the open circuit voltage and fill factor.

  2. Electrical characterization of annealed chemical-bath-deposited CdS films and their application in superstrate configuration CdTe/CdS solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Graf, A., E-mail: aleksandr.graf@gmail.com [Department of Physics, Tallinn University of Technology, 5 Ehitajate tee, 19086 Tallinn (Estonia); Department of Materials Science, Tallinn University of Technology, 5 Ehitajate tee, 19086 Tallinn (Estonia); Maticiuc, N.; Spalatu, N.; Mikli, V. [Department of Materials Science, Tallinn University of Technology, 5 Ehitajate tee, 19086 Tallinn (Estonia); Mere, A. [Department of Physics, Tallinn University of Technology, 5 Ehitajate tee, 19086 Tallinn (Estonia); Department of Materials Science, Tallinn University of Technology, 5 Ehitajate tee, 19086 Tallinn (Estonia); Gavrilov, A. [Department of Physics, Tallinn University of Technology, 5 Ehitajate tee, 19086 Tallinn (Estonia); Hiie, J. [Department of Materials Science, Tallinn University of Technology, 5 Ehitajate tee, 19086 Tallinn (Estonia)

    2015-05-01

    Application of chemical-bath-deposited CdS in the superstrate configuration of CdTe/CdS solar cells involving CdCl{sub 2}:O{sub 2} heat treatment of CdTe/CdS structures at about 400 °C is problematic. Namely, the vertical capillary surfaces (grain boundaries) between the columnar CdS grains perform as fast diffusion channels leading to the emergence of short circuits between the absorber and front contact. It was assumed that the grain boundaries contain residual hydroxy-oxide type compounds and form electrical barriers between columnar grains in the lateral direction of the CdS layer and that the electrical methods should be indicative of the behavior of grain boundaries in the annealing process. All samples were characterized by temperature dependence of DC conductivity in a temperature range of 50-300 K, X-ray diffraction, and scanning electron microscope. It has been found that the deeper layers of H{sub 2} and N{sub 2} annealed CdS preserve residual hydroxide, which released the gas phase in the recrystallization process of the chloride processing and created porosity on the CdTe/CdS interface. - Highlights: • We examine interface of CdS/CdTe structures after chloride heat treatment. • The mechanism of the formation of porosity in the CdS/CdTe interface is suggested. • Chloride heat treatment causes also recrystallization of CdS. • The gap between CdS and CdTe is minimal due to CdO on the grain boundaries of CdS.

  3. The correlation of electrical conductivity with the microstructure of Ge2Sb2Te5 thin films alloyed with Sn

    Science.gov (United States)

    Yin, Qixun; Chen, Leng

    2017-01-01

    In this research, the effects of Sn alloying on structure transformation and electrical characteristics of Ge2Sb2Te5 (GST) thin films were studied. It was discovered that the SnTe phase formed in GST thin films when Sn content exceeded 26 at%, and the addition of Sn atoms expanded the lattice parameter, as a result of atomic radii difference between Ge and Sn atoms. Furthermore, temperature dependent sheet resistance measurements on the GST:Sn thin films were performed for the electrical characteristics to be studied. Sn substitution fraction of 16 at% was discovered to maximize the crystallization temperature of GST thin films. Compared to the GST thin films, crystallization temperature difference and lower amorphous resistance of the GST:Sn thin films were mainly due to lower bonding energy of Sn–Te. Moreover, the amorphous conductivity activation energies (E σ) corresponding to different grain sizes were calculated with the Arrhenius equation. The E σ value of GST:Sn thin films decreased significantly as the Sn content increased due to grain size effects, which appears to improve the temperature stability of conductivity of phase change memory.

  4. Synthesis and Characterization of Folate Targeting CdTe/CdS Quantum Dots Fluorescent Probe%叶酸受体靶向的CdTe/CdS量子点荧光探针的制备和表征

    Institute of Scientific and Technical Information of China (English)

    江珊珊; 谢民强; 符小艺

    2013-01-01

    [Objective] To develop a CdTe/CdS quantum dots fluorescent probe (FA-PEG-CdTe/CdS) modified with folate receptor and to detect its targeting.[Methods] CdTe/CdS QD were synthesized in aqueous phase by using mercaptosuccinic acid (MSA) as stabilizer and linker.The spectral properties were investigated via fluorescence spectrophotometer and UV spectrophotometry.Crystal composition was determined via X-radial diffractometer.Morphology of the prepared QD was determined on a transmission electron microscopy (TEM).The folate receptor targeting quantum dots fluorescent probe FA-PEG-CdTe/CdS was made by coupling CdTe/CdS QD with FA-PEG-NH2.The Coupling effect was evaluated by agarose gel electrophoresis and spectral analysis.The cellular uptake in FR-positive human nasopharyngeal carcinoma cells (HNE-1cells) and FR-negative human nasopharyngeal carcinoma cells (CNE-2 cell) for FA-PEG-CdTe/CdS was found by means of inverted fluorescence microscopy.We can test the targeting property and specificity by observing the mark situation of different cells which cultured in different medium.[Result] In the condition of pH =10,n(Te2+):n(Cd2-):n(MSA) =1:10:10.5,with reaction time prolonging,the diameters of MSA-stabilized CdTe is increasing and the adsorption spectra and emission spectrum is constantly red shifting but the fluorescence quantum yield of CdTe QD is decreasing.The quantum yield of CdTe QD had reached 72.5% in the reaction of ten minutes.The XRD patterns of MSA-stabilized CdTe had proved the corresponding (111),(220),(311) lattice faces of cubic crystal CdTe.The picture of TEM show the CdTe particle size distribution is uniform and the average particle diameter is 3 nm (10 min).The agarose gel electrophoresis and spectral analysis proved that CdTe/CdS-PEG-FA is Stable.From the result of inverted fluorescence microscopy,FR-positive HNE-1,Hep-2 can be specific marked by FA-PEG-CdTe/CdS.[Conclusion] CdTe quantum dots can be used as a new fluorescent marking material.FAPEG-CdTe/Cd

  5. 近空间升华沉积CdTe多晶薄膜过程的研究%Study on close-space sublimating and depositing process of CdTe Polycrystalline films' Preparation

    Institute of Scientific and Technical Information of China (English)

    郑华靖; 张静全; 冯良桓; 郑家贵; 谢二庆

    2005-01-01

    研究了近空间升华(CSS)沉积CdTe多晶薄膜的物理机制,测量了近空间沉积装置内的温度分布,分析了升温过程、气压与薄膜的初期成核的关系,优化了升温过程,在此基础上制备出了转换效率优良的结构为SnO2:F/CdS/CdTe/Au的串联集成太阳电池.同时结果表明:近空间升华制备CdTe多晶薄膜的物理过程主要是,CdTe升华前升温,CdTe源升华分解为Cd、Te2,Cd、Te2在衬底上化合沉积以及衬底上的CdTe反升华等过程.在正常的近空间升华过程中,CdTe的蒸汽压远小于保护气体的气压.后者对对成核的晶粒方向几乎没有影响,但它通过改变分子平均自由程来影响Cd、Te2分子的扩散,从而影响薄膜的生长速率.

  6. Patterning thick diffused junctions on CdTe

    CERN Document Server

    Kalliopuska, Juha; Sipilä, Heikki; Andersson, Hans; Vähänen, Sami; Eränen, Simo; Tlustos, Lukas

    2009-01-01

    Dividing the detector crystal into discrete pixels enables making an imaging detector, in which the charge collected by each pixel can be read separately. Even if the detector is not meant for imaging, patterns on the crystal surface may be used as guard structures that control and limit the flow of charges in the crystal. This has been exceedingly hard for the detector crystals having thick diffused layers. The paper reports a patterning method of the thick diffused junctions on CdTe. The patterning method of In-diffused pn-junction on CdTe chip is demonstrated by using a diamond blade. The patterning is done by removing material from the pn-junction side of the chip, so that the trenches penetrate the diffused layer. As the trenches extend deeper into the bulk than the junction, the regions separated by the trench are electrically isolated. Electrical characterization results are reported for the strips separated by trenches with various depths. The strip isolation is clearly seen in both measured leakage c...

  7. Advanced CdTe Photovoltaic Technology: September 2007 - March 2009

    Energy Technology Data Exchange (ETDEWEB)

    Barth, K.

    2011-05-01

    During the last eighteen months, Abound Solar (formerly AVA Solar) has enjoyed significant success under the SAI program. During this time, a fully automated manufacturing line has been developed, fabricated and commissioned in Longmont, Colorado. The facility is fully integrated, converting glass and semiconductor materials into complete modules beneath its roof. At capacity, a glass panel will enter the factory every 10 seconds and emerge as a completed module two hours later. This facility is currently undergoing trials in preparation for large volume production of 120 x 60 cm thin film CdTe modules. Preceding the development of the large volume manufacturing capability, Abound Solar demonstrated long duration processing with excellent materials utilization for the manufacture of high efficiency 42 cm square modules. Abound Solar prototype modules have been measured with over 9% aperture area efficiency by NREL. Abound Solar demonstrated the ability to produce modules at industry leading low costs to NREL representatives. Costing models show manufacturing costs below $1/Watt and capital equipment costs below $1.50 per watt of annual manufacturing capacity. Under this SAI program, Abound Solar supported a significant research and development program at Colorado State University. The CSU team continues to make progress on device and materials analysis. Modeling for increased device performance and the effects of processing conditions on properties of CdTe PV were investigated.

  8. ADVANCED READOUT ELECTRONICS FOR MULTIELEMENT CdZnTe SENSORS.

    Energy Technology Data Exchange (ETDEWEB)

    DE GERONIMO,G.; O CONNOR,P.; KANDASAMY,A.; GROSHOLZ,J.

    2002-07-08

    A generation of high performance front-end and read-out ASICs customized for highly segmented CdZnTe sensors is presented. The ASICs, developed in a multi-year effort at Brookhaven National Laboratory, are targeted to a wide range of applications including medical, safeguards/security, industrial, research, and spectroscopy. The front-end multichannel ASICs provide high accuracy low noise preamplification and filtering of signals, with versions for small and large area CdZnTe elements. They implement a high order unipolar or bipolar shaper, an innovative low noise continuous reset system with self-adapting capability to the wide range of detector leakage currents, a new system for stabilizing the output baseline and high output driving capability. The general-purpose versions include programmable gain and peaking time. The read-out multichannel ASICs provide fully data driven high accuracy amplitude and time measurements, multiplexing and time domain derandomization of the shaped pulses. They implement a fast arbitration scheme and an array of innovative two-phase offset-free rail-to-rail analog peak detectors for buffering and absorption of input rate fluctuations, thus greatly relaxing the rate requirement on the external ADC. Pulse amplitude, hit timing, pulse risetime, and channel address per processed pulse are available at the output in correspondence of an external readout request. Prototype chips have been fabricated in 0.5 and 0.35 {micro}m CMOS and tested. Design concepts and experimental results are discussed.

  9. ISGRI: a CdTe array imager for INTEGRAL

    Science.gov (United States)

    Lebrun, Francois; Blondel, Claire; Fondeur, Irene; Goldwurm, Andrea; Laurent, Phillipe; Leray, Jean P.

    1996-10-01

    The INTEGRAL soft gamma-ray imager (ISGRI) is a large and thin CdTe array. Operating at room temperature, this gamma camera covers the lower part (below 200 keV) of the energy domain (20 keV - 10 MeV) of the imager on board the INTEGRAL Satellite (IBIS). The ASIC's front-end electronics features particularly a low noise preamplifier, allowing a threshold below 20 keV and a pulse rise-time measurement which permits a charge loss correction. The charge loss correction and its performances are presented as well as the results of various studies on CdTe thermal behavior and radiation hardness. At higher energy (above 200 keV) ISGRI will operate in conjunction with PICsIT, the IBIS CsI gamma camera. A selection among the events in coincidence performed on the basis of the Compton scattering properties reduces strongly the background. This allows an improvement of the sensitivity and permits short term imaging and spectral studies (high energy pulsars) which otherwise would not have fit within the IBIS telemetry allocation.

  10. Native Defect Control of CdTe Thin Film Solar Cells by Close-Spaced Sublimation

    Science.gov (United States)

    Okamoto, Tamotsu; Kitamoto, Shinji; Yamada, Akira; Konagai, Makoto

    2001-05-01

    The control of native defects in the CdTe thin film solar cells was investigated using a novel source for close-spaced sublimation (CSS) process which was prepared by vacuum evaporation with elemental Cd and Te (evaporated source). The evaporated sources were prepared on glass substrates at room temperature, and the Cd/Te ratio was controlled by varying the Cd and Te beam equivalent pressures. In the cells using the Te-rich source, the conversion efficiency was less than 0.2% because of the extremely low shunt resistance. On the other hand, a conversion efficiency above 15% was obtained by using the Cd-rich source. Capacitance-voltage (C-V) characteristics revealed that the acceptor concentration in the CdTe layer increased with increasing Cd/Te ratio of the evaporated source. Furthermore, photoluminescence spectra implied that the formation of the Cd vacancies in the CdTe layer was suppressed using the Cd-rich source.

  11. Electrical properties of liquid Cd-Te alloys

    Science.gov (United States)

    Moussa, A. Ben; Giordanengo, B.; Humbert, J. C.; Chaaba, H.; Bestandji, M.; Gasser, J. G.

    2000-12-01

    The electrical resistivity and the thermopower of liquid Cdx-Te1-x have been investigated experimentally as a function of temperature over the whole composition range. Due to the high melting point of Cd0.5Te0.5(1098 °C) and the low boiling points of cadmium (765 °C) and tellurium (990 °C), the measurements were difficult. Nevertheless, with a different experimental setup we were able to measure the resistivity and the thermopower from the liquidus up to 1200 °C. The resistivity shows a maximum at x=0.54 reaching a value of 13 000 μΩ cm at 1100 °C. A marked feature of liquid Cdx-Te1-x is that the thermopower varies rapidly from a positive value in the tellurium rich region to a negative value in the cadmium rich one around the equiatomic composition. The electronic properties, near this composition, were analyzed by using equations derived from the Kubo-Greenwood formula.

  12. Microwave-assisted synthesis of water-dispersed CdTe/CdSe core/shell type II quantum dots

    OpenAIRE

    Sai Li-Man; Kong Xiang Yang

    2011-01-01

    Abstract A facile synthesis of mercaptanacid-capped CdTe/CdSe (core/shell) type II quantum dots in aqueous solution by means of a microwave-assisted approach is reported. The results of X-ray diffraction and high-resolution transmission electron microscopy revealed that the as-prepared CdTe/CdSe quantum dots had a core/shell structure with high crystallinity. The core/shell quantum dots exhibit tunable fluorescence emissions by controlling the thickness of the CdSe shell. The photoluminescent...

  13. Development of monocrystalline CdTe solar cells for terrestrial applications, especially for optical concentrators

    Energy Technology Data Exchange (ETDEWEB)

    Jaeger, H.; Fuessl, B.; Seipp, E.; Thiel, R.

    1981-01-01

    During the first phase of the contract most of the work was done in order to optimise the most important structural elements of the solar cells, which were produced on the base of crystalline CdTe. Two approaches in development of such cells were made: n-CdTe crystals were covered with a p-type heterolayer as a window for sunlight; ZnTe was evaporated as a p-type layer. p-CdTe crystals were covered with a n-type heterolayer as a window. Here, CdS evaporation layers and indium-tin-oxide (ITO) sputtered layers were applied. Within the first approach the realisation of ZnTe-layers simultaneously highly conductive and transparent was tried by using numerous dopants. Within the second approach, the development of p-CdTe/n-CdS solar cells, the resistances of the ohmic contacts on the back of the p-CdTe wafers were a major problem. We found some ways of preparing ohmic contacts of acceptable contact resistance, but an ideal problem solution is lacking still. We found a dependence of the contact resistance on the p-CdTe doping concentration. Solar cells made from p-CdTe crystals covered with n/sup +/-CdS attained an open circuit voltage of 655 mV and a short circuit current density of 13.8 mA/cm/sup 2/ in a 100 mW/cm/sup 2/ light. Assuming a sufficiently low series resistance we expect an efficiency of about 6 percent. Besides the n/sup +/-CdS layers n/sup +/-ITO-layers (indium-tin-oxide) were deposited on p-CdTe by sputtering. These cells exhibit a short circuit density a little higher but a lower open circuit voltage than the heterosolarcells with n/sup +/-CdS.

  14. Effects of Sn Substitution on Thermoelectric Properties of Ge4SbTe5

    Science.gov (United States)

    Williams, Jared B.; Mather, Spencer; Morelli, Donald T.

    2016-02-01

    Phase-change materials are identified by their ability to rapidly alternate between amorphous and crystalline phases upon heating, exhibiting large contrast in the optical/electrical properties of the respective phases. Such materials are primarily used in memory storage applications, but recently they have also been identified as potential thermoelectric materials. Many of the phase-change materials studied today can be found on the pseudobinary (GeTe)1- x (Sb2Te3) x tie-line. Ge4SbTe5, a single-phase compound just off of the (GeTe)1- x (Sb2Te3) x tie-line, forms in a metastable rocksalt crystal structure at room temperature. It has been found that stoichiometric and undoped Ge4SbTe5 exhibits thermal conductivity of ~1.2 W/m-K at high temperature and a dramatic decrease in electrical resistivity at 623 K due to a structural phase transition, which leads to a large enhancement in both thermoelectric power factor and thermoelectric figure of merit at 823 K. Introducing point defects via isoelectronic substitutions can be an effective means of reducing thermal conductivity and enhancing thermoelectric performance. We present a study of the effects of Sn substitution for Ge on the electrical and thermal transport properties of Ge4SbTe5.

  15. Interface chemistry of CdZnTe films studied by a peel-off approach

    Science.gov (United States)

    Tao, Jun; Xu, Haitao; Zhang, Yuelu; Ji, Huanhuan; Xu, Run; Huang, Jian; Zhang, Jijun; Liang, Xiaoyan; Tang, Ke; Wang, Linjun

    2016-12-01

    CdZnTe films with thickness above 50 μm were deposited at temperatures of 200-500 °C by Close Space Sublimation method. A peel-off approach has been adopted to study the interface chemistry of CdZnTe thick films. For all the CdZnTe films, the scanning electron microscopy images show the small and round-like grains formed at interface in contrast to the large ordered grains at surface. For CdZnTe films grown at a low substrate temperature of 200 °C, the interface layer between CdZnTe and substrate is mixed with Te and CdTe, as evidenced by X-ray diffraction, Raman and X-ray photoelectron spectroscopy results. The thickness of the interface layer can be estimated to be 84 nm by depth profile using X-ray photoelectron spectroscopy. In contrast, a thin interface layer less than 14 nm is found at a high substrate temperature of 500 °C. The limited reaction of Te2 and Cd (Zn) to CdZnTe at a low growth temperature is responsible for the formation of the thick interface layer and a slow deposition rate at the nucleation stage.

  16. Effects of high-temperature annealing on ultra-thin CdTe solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Xia Wei; Lin Hao; Wu, Hsiang N.; Tang, Ching W., E-mail: chtang@che.rochester.edu

    2011-10-31

    High-temperature annealing (HTA), a process step prior to vapor cadmium chloride (VCC) treatment, has been found to be useful for improving the crystallinity of CdTe films and the efficiency of ultra-thin CdTe solar cells. Scanning electron microscopy, optical absorption, photoluminescence measurements and analyses on photoluminescence results using spectral deconvolution reveal that the additional HTA step produces substantial grain growth and reduces grain boundary defects. It also reduces excessive sulfur diffusion across the junction that can occur during the VCC treatment. The HTA step helps to produce pinhole-free CdTe films and reduce electrical shorts in ultra-thin CdTe solar cells. An efficiency of about 11.6% has been demonstrated for ultra-thin CdS/CdTe solar cells processed with HTA step.

  17. 太阳电池中CdTe多晶薄膜沉积制备及其性能%The Preparation and Properties of CdTe Polycrystalline Films for Solar Cells

    Institute of Scientific and Technical Information of China (English)

    郑华靖; 张静全; 冯良桓; 蔡伟; 郑家贵; 谢二庆

    2005-01-01

    在氩氧混合气氛下近空间升华技术(CSS)制备CdTe多晶薄膜中,薄膜的结构、性质决定于整个沉积过程.深入研究沉积过程中的热交换、物质输运,有助于制备薄而致密的具有进行良好光电性质CdTe薄膜.通过分析近空间沉积的物理机制,测量近空间沉积装置内温度分布,对升温过程、气压与薄膜初期成核的关系进行讨论.研究结果表明,不同气压下制备的样品,均有立方相CdTe,此外,还有CdS和SnO2:F衍射峰,CdTe晶粒随气压增加有减小趋势;随气压的增加,透过率呈下降趋势,相应的CdTe吸收边向短波方向移动.在此基础上制备出转换效率优良的结构为SnO2:F/CdS/CdTe/Au的串联集成电池.

  18. Optimization of High-Efficiency CdS/CdTe Thin Film Solar Cell Using Step Doping Grading and Thickness of the Absorption Layer

    OpenAIRE

    Masoud Sabaghi; Abbas Majdabadi; Saeid Marjani; Saeed Khosroabadi

    2015-01-01

    In this paper, the influence of stepped doping of the absorber layer on performance of Cadmium Sulfide/Cadmium Telluride (CdS/CdTe) solar cell has been investigated. At first, the electrical characteristics of conventional CdS/CdTe solar cell is validated with fabricated CdS/CdTe solar cell. To improve the maximum efficiency of CdS/CdTe solar cell, the doping and thickness of the absorption layer are optimized. By step doping concentration within the absorber layer using buffer layer back con...

  19. Defect energetics and magnetic properties of 3 d-transition-metal-doped topological crystalline insulator SnTe

    Science.gov (United States)

    Wang, Na; Wang, JianFeng; Si, Chen; Gu, Bing-Lin; Duan, WenHui

    2016-08-01

    The introduction of magnetism in SnTe-class topological crystalline insulators is a challenging subject with great importance in the quantum device applications. Based on the first-principles calculations, we have studied the defect energetics and magnetic properties of 3 d transition-metal (TM)-doped SnTe. We find that the doped TM atoms prefer to stay in the neutral states and have comparatively high formation energies, suggesting that the uniform TMdoping in SnTe with a higher concentration will be difficult unless clustering. In the dilute doping regime, all the magnetic TMatoms are in the high-spin states, indicating that the spin splitting energy of 3 d TM is stronger than the crystal splitting energy of the SnTe ligand. Importantly, Mn-doped SnTe has relatively low defect formation energy, largest local magnetic moment, and no defect levels in the bulk gap, suggesting that Mn is a promising magnetic dopant to realize the magnetic order for the theoretically-proposed large-Chern-number quantum anomalous Hall effect (QAHE) in SnTe.

  20. Size and temperature effects on electric properties of CdTe/ZnTe quantum rings

    Institute of Scientific and Technical Information of China (English)

    Woo-Pyo Hong; Seoung-Hwan Park

    2011-01-01

    The electronic properties of CdTe/ZnTe quantum rings (QRs) are investigated as functions of size and temperature using an eight-band strain-dependent k-p Hamiltonian. The size effects of diameter and height on the strain distributions around the QRs are studied. We find that the interband transition energy,defined as the energy difference between the ground electronic and the ground heavy-hole subbands,increases with the increasing QR inner diameter regardless of the temperature,while the interband energy decreases with the increasing QR height. This is attributed to the reduction of subband energies in both the conduction and the valence bands due to the strain effects. Our model,in the framework of the finite element method and the theory of elasticity of solids,shows a good agreement with the temperature-dependent photoluminescence measurement of the interband transition energies.

  1. Single-Crystal CdTe Homojunction Structures for Solar Cell Applications

    Science.gov (United States)

    Su, Peng-Yu; Dahal, Rajendra; Wang, Gwo-Ching; Zhang, Shengbai; Lu, Toh-Ming; Bhat, Ishwara B.

    2015-09-01

    We report two different CdTe homojunction solar cell structures. Single-crystal CdTe homojunction solar cells were grown on GaAs single-crystal substrates by metalorganic chemical vapor deposition. Arsenic and iodine were used as dopants for p-type and n-type CdTe, respectively. Another homojunction solar cell structure was fabricated by growing n-type CdTe directly on bulk p-type CdTe single-crystal substrates. The electrical properties of the different layers were characterized by Hall measurements. When arsine was used as arsenic source, the highest hole concentration was ~6 × 1016 cm-3 and the activation efficiency was ~3%. Very abrupt arsenic doping profiles were observed by secondary ion mass spectrometry. For n-type CdTe with a growth temperature of 250°C and a high Cd/Te ratio the electron concentration was ~4.5 × 1016 cm-3. Because of the 300 nm thick n-type CdTe layer, the short circuit current of the solar cell grown on the bulk CdTe substrate was less than 10 mA/cm2. The open circuit voltage of the device was 0.86 V. According to a prediction based on measurement of short circuit current density ( J sc) as a function of open circuit voltage ( V oc), an open circuit voltage of 0.92 V could be achieved by growing CdTe solar cells on bulk CdTe substrates.

  2. Donor states in a semimagnetic Cd1 -xinMnxin Te /Cd1 -xoutMnxout Te Double Quantum Well

    Science.gov (United States)

    Kalpana, Panneer Selvam; Nithiananthi, Perumal; Jayakumar, Kalyanasundaram

    2017-02-01

    The theoretical investigation has been carried out on the binding energy of donor associated with the electrons confined in a Cd1 -xinMnxin Te /Cd1 -xoutMnxout Te Double Quantum Well (DQW) as a function of central barrier width for various well dimensions and impurity locations in the barrier and the well. The magnetic field can act as a tool to continuously change the interwell coupling inside this DQW systems and its effect on donor binding has also been studied. Moreover, the polaronic corrections, which is due to the strong exchange interaction between the magnetic moment of Mn2+ ion and the spin of the confined carrier, to the binding energy of the hydrogenic donor impurity has also been estimated with and without the application of magnetic field. The binding energy of the donor impurity is determined by solving the Schrodinger equation variationally in the effective mass approximation and the effect due to Bound Magnetic Polaron (BMP) is included using mean field theory with the modified Brillouin function. The results are reported and discussed.

  3. Cd-Te-In oxide thin films as possible transparent buffer layer in CdTe based solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Castro-Rodriguez, R; Camacho, J M; Pena, J L [Applied Physics Department, CINVESTAV-IPN Merida, C.P. 97310, Merida, Yucatan (Mexico); Martel, A; Mendez-Gamboa, J, E-mail: romano@mda.cinvestav.m [Facultad de Ingenieria, Universidad Autonoma de Yucatan. AP 150 Cordemex, 97310 Merida, Yucatan (Mexico)

    2009-05-01

    Cd-Te-In-oxide thin films were grown by Pulsed Laser Deposition (PLD) technique using CdTe powder embedded in a matrix of indium metallic as target. The films were deposited at different oxygen pressures (P{sub o2}) from 15 to 50 mTorr at substrate temperature of 420{sup 0}C. Sheet resistance (R{sub sheet}) and transmission spectrum were measured as a function of P{sub o2}. From measurements of optical transmission, the Photonic Flux Density (PFD) spectrum were obtained and the integral of these PFD for each film were evaluated between energy range of 1.5 eV and 2.4 eV for obtain the amount of photons that can be transferred across the film in this range of solar energy spectrum. These values were evaluated over the R{sub sheet} to be used as a figure of merit. The best choice in our conditions was the films with P{sub o2} =28.5 mTorr, where the figure of merit reaches the maximum value.

  4. Long-Term Stable Surface Treatments on CdTe and CdZnTe Radiation Detectors

    Science.gov (United States)

    Pekarek, Jakub; Belas, Eduard; Zazvorka, Jakub

    2017-04-01

    The spectral resolution and charge collection efficiency (CCE) of cadmium telluride (CdTe) and cadmium zinc telluride (CZT) room-temperature x-ray and gamma-ray detectors are often limited by high surface leakage current due to conducting surface species created during detector fabrication. Surface treatments play a major role in reduction of this surface leakage current. The effect of various types of surface etching and passivation on the leakage current and thereby the spectral energy resolution, CCE, and internal electric field profile of CdTe/CZT detectors has been studied. The main aim of this work is preparation of long-term stable detectors with strongly reduced leakage current. The time stability of the current-voltage characteristic and spectral resolution was investigated during 21 days and 1 year, respectively, after performing surface treatments. Our results suggest that the optimal detector preparation method is chemomechanical polishing in bromine-ethylene glycol solution followed by chemical etching in bromine-methanol solution then surface passivation in potassium hydroxide or ammonium fluoride (NH4F/H2O2). Detectors prepared using this optimal treatment exhibited low leakage current, high spectral resolution, and long-term stability compared with those subjected to other surface preparation methods.

  5. Long-Term Stable Surface Treatments on CdTe and CdZnTe Radiation Detectors

    Science.gov (United States)

    Pekarek, Jakub; Belas, Eduard; Zazvorka, Jakub

    2016-12-01

    The spectral resolution and charge collection efficiency (CCE) of cadmium telluride (CdTe) and cadmium zinc telluride (CZT) room-temperature x-ray and gamma-ray detectors are often limited by high surface leakage current due to conducting surface species created during detector fabrication. Surface treatments play a major role in reduction of this surface leakage current. The effect of various types of surface etching and passivation on the leakage current and thereby the spectral energy resolution, CCE, and internal electric field profile of CdTe/CZT detectors has been studied. The main aim of this work is preparation of long-term stable detectors with strongly reduced leakage current. The time stability of the current-voltage characteristic and spectral resolution was investigated during 21 days and 1 year, respectively, after performing surface treatments. Our results suggest that the optimal detector preparation method is chemomechanical polishing in bromine-ethylene glycol solution followed by chemical etching in bromine-methanol solution then surface passivation in potassium hydroxide or ammonium fluoride (NH4F/H2O2). Detectors prepared using this optimal treatment exhibited low leakage current, high spectral resolution, and long-term stability compared with those subjected to other surface preparation methods.

  6. Preparation and characterization of pulsed laser deposited a novel CdS/CdSe composite window layer for CdTe thin film solar cell

    Science.gov (United States)

    Yang, Xiaoyan; Liu, Bo; Li, Bing; Zhang, Jingquan; Li, Wei; Wu, Lili; Feng, Lianghuan

    2016-03-01

    A novel CdS/CdSe composite window structure was designed and then the corresponding films were prepared by pulsed laser deposition as an improved window layer for CdTe-based solar cells. Two types of this composite window structure with 5 cycles and 10 cycles CdS/CdSe respectively both combined with CdS layers were prepared at 200 °C compared with pure CdS window layer and finally were applied into CdTe thin film solar cells. The cross section and surface morphology of the two composite window layers were monitored by using scanning electron microscopy and the result shows that the pulsed laser deposited composite window layers with good crystallinity are stacking together as the design. The devices based on CdS/CdSe composite window layers have demonstrated the enhanced photocurrent collection from both short and long wavelength regions compared to CdS/CdTe solar cell. The efficiency of the best reference CdS/CdTe solar cell was 10.72%. And the device with 5 cycles CdS/CdSe composite window showed efficiency of 12.61% with VOC of 772.92 mV, JSC of 25.11 mA/cm2 and FF of 64.95%. In addition, there are some differences which exist within the optical transmittance spectra and QE curves between the two CdS/CdSe composite window samples, indicating that the volume proportion of CdSe may influence the performance of CdTe thin film solar cell.

  7. Growth of p-CdTe thin films on n-GaN/sapphire

    Science.gov (United States)

    Jung, Younghun; Chun, Seunju; Kim, Donghwan; Kim, Jihyun

    2011-07-01

    CdTe thin film was successfully grown on GaN/Sapphire substrate using a close spaced sublimation (CSS) system for the applications in solar cells. CdTe thin film was characterized by SEM, micro-Raman spectroscopy, and X-ray diffraction. The growth rate was 1 μm/min. In addition, we confirmed that CdCl 2 treatment beneficially influenced the structure and composition of the CdTe thin films. CdCl 2 treatment which has been known that it improved the efficiency of the CdS/CdTe solar cells, produced similar positive effects such as increasing the CdTe grain size and reducing the number of pin-holes. The growth of the CdTe thin film by CSS method produced nominal effects on biaxial strain and carrier concentrations in the GaN/Sapphire substrate. The CdTe thin film grown on the GaN/Sapphire substrate holds great promise for use in solar cell applications due to its several advantages.

  8. Spectrum-per-Pixel Cathodoluminescence Imaging of CdTe Thin-Film Bevels

    Energy Technology Data Exchange (ETDEWEB)

    Moseley, John; Al-Jassim, Mowafak M.; Burst, James; Guthrey, Harvey L.; Metzger, Wyatt K.

    2016-11-21

    We conduct T=6 K cathodoluminescence (CL) spectrum imaging with a nano-scale electron beam on beveled surfaces of CdTe thin-films at different critical stages of standard CdTe device fabrication. The through-thickness total CL intensity profiles are consistent with a reduction in grain boundary recombination due to the CdCl2 treatment. Color-coded maps of the low-temperature luminescence transition energies reveal that CdTe thin films have remarkably non-uniform opto-electronic properties, which depend strongly on sample processing history. The grain-to-grain S content in the interdiffused CdTe/CdS region is estimated from a sample size of thirty-five grains, and the S content in adjacent grains varies significantly in CdCl2-treated samples. A low-temperature luminescence model is developed to interpret spectral behavior at grain boundaries and grain interiors.

  9. Electronic properties of an exciton in CdTe/CdSe/CdTe/CdSe type-II nano-heterostructure

    Science.gov (United States)

    Suseel Rahul, K.; Salini, K.; Mathew, Vincent

    2016-11-01

    In this study, we have carried out a detailed theoretical investigation on the binding energy of an exciton in type-II CdTe/CdSe core/shell/well/shell (CSWS) nanocrystal quantum dot (NCQD) in the strong confinement region. The calculations are based on the effective mass approximation, and the coulombic interaction between electron and hole is introduced using Hartree approximation. With these theoretical basis, the coupled Poisson-Schrodinger equations are solved in a self consistent iterative manner. In strong confinement regime, the binding energy variation with core radius in type-II NCQD shows a peak. And this peak widens for larger well width and inner shell thickness. Our study suggests that, this anomalous behavior of exciton binding energy is due to an effect called ‘positional flip of exciton’, caused by the faster tunneling of hole to the inner layer in comparison with electron. Our results can be applied in laser and optoelectronic engineering for designing more efficient optoelectronic devices.

  10. Spectroscopic study on the doping of polycrystalline CdTe layers for solar cells; Spektroskopische Untersuchungen zur Dotierung von polykristallinen CdTe-Schichten fuer Solarzellen

    Energy Technology Data Exchange (ETDEWEB)

    Kraft, Christian

    2011-11-29

    First in the present thesis the fundamental properties of CdTe are described. In the following it is discussed, how a CdTe solar cell is generally constructed, which specialities are to be regarded, and how an improvement of the actually reachable data of such a solar cell in view of the efficiency can be reached fundamentally and in then practical realization. In the third chapter the physical foundations of the most important methods are discussed, which are applied in the framework of this thesis for the analysis of the CdTe layers. The fourth chapter describes the details of the experiments of this thesis. The fifth chapter deals with the analysis of the photoluminescence of CdTe layers. Special attention is put on the analysis of the excitonic luminescence. The sixth chapter treats the implantation of CdTe layers with phosphor. The influence of phosphorus as dopant on the PL spectra of CdTe and the correponding characteristics of implanted solar cells are presented. Also the influence of radiation damages as consequence of the ion implantation is studied in this chapter by means of the analysis of differently thick absorber layers. In the seventh chapter finally a new procedure for the fabrication of solar cells on the base of CdTe as absorber material is introduced, which shall make possible to change the stoichiometry of cadmium mand tellurium specifically and to present additionally a suited material, in order to form the doping of CdTE a solar-cell material variably. The fundamental properties of the new facility are experimentally determined, and first solar cells are fabricated with this facility and analyzed. Also an in-situ doping with phosphorus is thereby performed and the result studied.

  11. Computational discovery of ferromagnetic semiconducting single-layer CrSnTe3

    Science.gov (United States)

    Zhuang, Houlong L.; Xie, Yu; Kent, P. R. C.; Ganesh, P.

    2015-07-01

    Despite many single-layer materials being reported in the past decade, few of them exhibit magnetism. Here we perform first-principles calculations using accurate hybrid density functional methods (HSE06) to predict that single-layer CrSnTe3 (CST) is a ferromagnetic semiconductor, with band gaps of 0.9 and 1.2 eV for the majority and minority spin channels, respectively. We determine the Curie temperature as 170 K, significantly higher than that of single-layer CrSiTe3 (90 K) and CrGeTe3 (130 K). This is due to the enhanced ionicity of the Sn-Te bond, which in turn increases the superexchange coupling between the magnetic Cr atoms. We further explore the mechanical and dynamical stability and strain response of this single-layer material for possible epitaxial growth. Our study provides an intuitive approach to understand and design single-layer magnetic semiconductors for a wide range of spintronics and energy applications.

  12. Aqueous synthesis of type-II CdTe/CdSe core-shell quantum dots for fluorescent probe labeling tumor cells.

    Science.gov (United States)

    Zeng, Ruosheng; Zhang, Tingting; Liu, Jincheng; Hu, Song; Wan, Qiang; Liu, Xuanming; Peng, Zhiwei; Zou, Bingsuo

    2009-03-04

    In this paper, we report a two-step aqueous synthesis of highly luminescent CdTe/CdSe core/shell quantum dots (QDs) via a simple method. The emission range of the CdTe/CdSe QDs can be tuned from 510 to 640 nm by controlling the thickness of the CdSe shell. Accordingly, the photoluminescence quantum yield (PL QY) of CdTe/CdSe QDs with an optimized thickness of the CdSe shell can reach up to 40%. The structures and compositions of the core/shell QDs were characterized by transmission electron microscopy, x-ray diffraction, and x-ray photoelectron spectroscopy experiments, and their formation mechanism is discussed. Furthermore, folate conjugated CdTe/CdSe QDs in Hela cells were assessed with a fluorescence microscope. The results show that folate conjugated CdTe/CdSe QDs could enter tumor cells efficiently.

  13. Temperature-dependent photoluminescence of highly luminescent water-soluble CdTe quantum dots

    Institute of Scientific and Technical Information of China (English)

    Ji Wei Liu; Yu Zhang; Cun Wang Ge; Yong Long Jin; Sun Ling Hu; Ning Gu

    2009-01-01

    Highly luminescent water-soluble CdTe quantum dots (QDs) have been synthesized with an electrogenerated precursor. The obtained CdTe QDs can possess good crystallizability, high quantum yield (QY) and favorable stability. Furthermore, a detection system is designed firstly for the investigation of the temperature-dependent PL of the QDs.

  14. Phosphorus Diffusion Mechanisms and Deep Incorporation in Polycrystalline and Single-Crystalline CdTe

    Energy Technology Data Exchange (ETDEWEB)

    Colegrove, Eric; Harvey, Steven P.; Yang, Ji-Hui; Burst, James M.; Albin, David S.; Wei, Su-Huai; Metzger, Wyatt K.

    2016-05-01

    A key challenge in cadmium telluride (CdTe) semiconductors is obtaining stable and high hole density. Group I elements substituting Cd can form ideal acceptors but easily self-compensate and diffuse quickly. For example, CdTe photovoltaics have relied on copper as a dopant, but copper creates stability problems and hole density that has not exceeded 1015 cm-3. If hole density can be increased beyond 10^16 cm-3, CdTe solar technology can exceed multicrystalline silicon and provide levelized costs of electricity below conventional energy sources. Group V elements substituting Te offer a solution, but are very difficult to incorporate. Using time-of-flight secondary-ion mass spectrometry, we examine bulk and grain boundary (GB) diffusion of phosphorous (P) in CdTe in Cd-rich conditions. We find that in addition to slow bulk diffusion and fast GB diffusion, there is a fast bulk diffusion component that enables deep P incorporation in CdTe. Detailed first-principles calculations indicate the slow bulk diffusion component is caused by substitutional P diffusion through the Te sublattice, whereas the fast bulk diffusion component is caused by P diffusing through interstitial lattice sites following the combination of a kick-out step and two rotation steps. The latter is limited in magnitude by high formation energy, but is sufficient to manipulate P incorporation. In addition to an increased physical understanding, this result opens up new experimental possibilities for Group V doping in CdTe materials.

  15. Fractal features of CdTe thin films grown by RF magnetron sputtering

    Science.gov (United States)

    Hosseinpanahi, Fayegh; Raoufi, Davood; Ranjbarghanei, Khadijeh; Karimi, Bayan; Babaei, Reza; Hasani, Ebrahim

    2015-12-01

    Cadmium telluride (CdTe) thin films were prepared by RF magnetron sputtering on glass substrates at room temperature (RT). The film deposition was performed for 5, 10, and 15 min at power of 30 W with a frequency of 13.56 MHz. The crystal structure of the prepared CdTe thin films was studied by X-ray diffraction (XRD) technique. XRD analyses indicate that the CdTe films are polycrystalline, having zinc blende structure of CdTe irrespective of their deposition time. All CdTe films showed a preferred orientation along (1 1 1) crystalline plane. The surface morphology characterization of the films was studied using atomic force microscopy (AFM). The quantitative AFM characterization shows that the RMS surface roughness of the prepared CdTe thin films increases with increasing the deposition time. The detrended fluctuation analysis (DFA) and also multifractal detrended fluctuation analysis (MFDFA) methods showed that prepared CdTe thin films have multifractal nature. The complexity, roughness of the CdTe thin films and strength of the multifractality increase as deposition time increases.

  16. Performance updating of CdZnTe strip-drift detectors

    DEFF Research Database (Denmark)

    Shorohov, M.; Tsirkunova, I.; Loupilov, A.;

    2007-01-01

    59.6 and 662 keV correspondingly. Recently, significant progress was done in CdZnTe crystals growth technology. In the present paper we present preliminary result of performance updating of CdZnTe strip-drift detectors based on crystal of 10 x 10 x 6 mm 3 produced by Yinnel Tech company. Results...

  17. Neutron scattering studies of Cd1−xMnxTe

    DEFF Research Database (Denmark)

    Giebultowicz, T.; Lebech, Bente; Buras, B;

    1984-01-01

    The diluted magnetic (‘‘semimagnetic’’) semiconductor Cd1–xMnxTe reveals intriguing spin glass properties. In this paper, the results of neutron scattering studies of Cd1–xMnxTe are presented. The low‐temperature spin correlations have been studied for several single crystal samples...

  18. Progress in MOCVD growth of HgCdTe epilayers for HOT infrared detectors

    Science.gov (United States)

    Kebłowski, A.; Gawron, W.; Martyniuk, P.; Stepień, D.; Kolwas, K.; Piotrowski, J.; Madejczyk, P.; Kopytko, M.; Piotrowski, A.; Rogalski, A.

    2016-05-01

    In this paper we present progress in MOCVD growth of (100) HgCdTe epilayers achieved recently at the Institute of Applied Physics, Military University of Technology and Vigo System S.A. It is shown that MOCVD technology is an excellent tool in fabrication of different HgCdTe detector structures with a wide range of composition, donor/acceptor doping and without post grown annealing. Particular progress has been achieved in the growth of (100) HgCdTe epilayers for long wavelength infrared photoconductors operated in HOT conditions. The (100) HgCdTe photoconductor optimized for 13-μm attain detectivity equal to 6.5x109 Jones and therefore outperform its (111) counterpart. The paper also presents technological progress in fabrication of MOCVD-grown (111) HgCdTe barrier detectors. The barrier device performance is comparable with state-of-the-art of HgCdTe photodiodes. The detectivity of HgCdTe detectors is close to the value marked HgCdTe photodiodes. Dark current densities are close to the values given by "Rule 07".

  19. Electrical properties anisotype heterojunctions n-TiO2:Mn/p-CdTe

    Directory of Open Access Journals (Sweden)

    Mostovyi A. I.

    2013-02-01

    Full Text Available The authors have investigated electronic properties of n-TiO2:Mn/p-CdTe anisotype heterojunctions, produced by the method of electron-beam evaporation of TiO2:Mn film on single-crystal CdTe substrates in vacuum. The dominant mechanism of charge transport in the forward and reverse bias has been established.

  20. Fabrication of the structures with autocatalytic CdTe nanowires using magnetron sputtering deposition

    Science.gov (United States)

    Soshnikov, I. P.; Semenov, A. A.; Belyavskii, P. Yu.; Shtrom, I. V.; Kotlyar, K. P.; Lysak, V. V.; Kudryashov, D. A.; Pavlov, S. I.; Nashchekin, A. V.; Cirlin, G. E.

    2016-12-01

    We report the possibility of autocatalytic synthesis of highly crystalline perfect CdTe nanowires by magnetron presputtering deposition through the windows in ultrathin layers of SiO2. The photoluminescence spectra of obtained CdTe nanowires exhibit an emission band in the 1.4-1.7 eV region, indicating crystalline perfection of the nanowires.

  1. Solution-processing of ultra-thin CdTe/ZnO nanocrystal solar cells

    Energy Technology Data Exchange (ETDEWEB)

    MacDonald, Brandon I. [CSIRO, Materials Science and Engineering, Bayview Ave, Clayton, Victoria, 3168 (Australia); School of Chemistry and Bio21 Institute, The University of Melbourne, Parkville, Victoria, 3010 (Australia); Gengenbach, Thomas R.; Watkins, Scott E. [CSIRO, Materials Science and Engineering, Bayview Ave, Clayton, Victoria, 3168 (Australia); Mulvaney, Paul [School of Chemistry and Bio21 Institute, The University of Melbourne, Parkville, Victoria, 3010 (Australia); Jasieniak, Jacek J., E-mail: Jacek.Jasieniak@csiro.au [CSIRO, Materials Science and Engineering, Bayview Ave, Clayton, Victoria, 3168 (Australia)

    2014-05-02

    We have carried out a detailed study into how modifications of the physical, chemical and optical properties of solution-processed, nanocrystalline CdTe layers influence the photovoltaic performance of sintered CdTe/ZnO nanocrystal solar cells. Such solar cells are fabricated through layer-by-layer assembly, which is enabled through an inter layer chemical and thermal treatment cycle. In this manner we are able to fabricate working solar cells with sintered CdTe layers as low as 90 nm, provided that grain size is precisely controlled. We show that the extent of grain growth achieved during the CdTe sintering process is strongly dependent on nanocrystal surface chemistry and chemical environment, with the removal of the organic capping ligands and the introduction of CdCl{sub 2} prior to annealing leading to greatly enhanced growth. Due to the air processing involved and the nanocrystalline nature of the CdTe, the overall performance of these solar cells is shown to be strongly dependent on both annealing temperature and time, with optimal results requiring a balance between crystal growth and degradation due to oxidation. Using this simple bi-layer device structure, optimized treatment conditions result in power conversion efficiencies of up to 7.7% and peak internal quantum efficiencies in excess of 95%. - Highlights: • We study the growth of nanocrystalline CdTe thin films from colloidal nanocrystals. • We examine the CdTe growth profiles as a function of surface chemistry. • We show that nanocrystalline CdTe is susceptible to oxidation under air annealing. • We show how this oxidation influences performance in CdTe/ZnO solar cells. • We demonstrate CdTe/ZnO solar cells with an efficiency of 7.7% fabricated in air.

  2. Evolution of oxygenated cadmium sulfide (CdS:O) during high-temperature CdTe solar cell fabrication

    Energy Technology Data Exchange (ETDEWEB)

    Meysing, Daniel M.; Reese, Matthew O.; Warren, Charles W.; Abbas, Ali; Burst, James M.; Mahabaduge, Hasitha P.; Metzger, Wyatt K.; Walls, John M.; Lonergan, Mark C.; Barnes, Teresa M.; Wolden, Colin A.

    2016-12-01

    Oxygenated cadmium sulfide (CdS:O) produced by reactive sputtering has emerged as a promising alternative to conventional CdS for use as the n-type window layer in CdTe solar cells. Here, complementary techniques are used to expose the window layer (CdS or CdS:O) in completed superstrate devices and combined with a suite of materials characterization to elucidate its evolution during high temperature device processing. During device fabrication amorphous CdS:O undergoes significant interdiffusion with CdTe and recrystallization, forming CdS1-yTey nanocrystals whose Te fraction approaches solubility limits. Significant oxygen remains after processing, concentrated in sulfate clusters dispersed among the CdS1-yTey alloy phase, accounting for ~30% of the post-processed window layer based on cross-sectional microscopy. Interdiffusion and recrystallization are observed in devices with un-oxygenated CdS, but to a much lesser extent. Etching experiments suggest that the CdS thickness is minimally changed during processing, but the CdS:O window layer is reduced from 100 nm to 60-80 nm, which is confirmed by microscopy. Alloying reduces the band gap of the CdS:O window layer to 2.15 eV, but reductions in thickness and areal density improve its transmission spectrum, which is well matched to device quantum efficiency. The changes to the window layer in the reactive environments of device fabrication are profoundly different than what occurs by thermal annealing in an inert environment, which produced films with a band gap of 2.4 eV for both CdS and CdS:O. These results illustrate for the first time the significant changes that occur to the window layer during processing that are critical to the performance of CdTe solar cells.

  3. Electronic structure and properties of Cd4As2Br3 and Cd4Sb2I3, analogues of CdSe and CdTe

    Science.gov (United States)

    Roy, Anand; Suchitra; Manjunath, K.; Ahmad, Tokeer; Waghmare, Umesh V.; Rao, C. N. R.

    2017-04-01

    Substitution of aliovalent anions in metal oxides and chalcogenides significantly affects the electronic structure and properties of the materials. Thus, substitution of P3- and Cl- in CdS decreases the band gap and favorably influences the photocatalytic activity. Complete substitution of a trivalent (A3-) and a monovalent (B-) anions in a cadmium chalcogenides, CdX, should give rise to a material of the composition Cd A0.5B0.5 or Cd2AB, but a compound with the composition Cd4P2Cl3 (or Cd2PCl1.5) is obtained in the case of CdS. We have investigated the analogous compounds, Cd4As2Br3 and Cd4Sb2I3, wherein the anions in CdSe and CdTe are substituted by As, Br and Sb, I respectively. These compounds are direct band gap semiconductors with a band gap of 1.8-1.9 eV and a photoluminescence band in the visible region. First-principles calculations show both Cd4As2Br3 and Cd4Sb2I3 to be direct band gap semiconductors. The arsenic bromide is predicted to be photochemically more active for HER than the antimony iodide.

  4. In-beam studies of {sup 98}Cd and {sup 102}Sn

    Energy Technology Data Exchange (ETDEWEB)

    Lipoglavsek, M. [Uppsala Univ. (Sweden)]|[J. Stefan Institute, Ljubljana (Slovenia); Gorska, M.; Schubart, R. [GSI, Darmstadt (Germany)] [and others

    1996-12-31

    For the first time excited states of the neutron deficient nuclei {sup 98}Cd and {sup 102}Sn were identified using in-beam spectroscopy following fusion evaporation reactions. Half lives of long lived isomeric states in both nuclei were also measured. Due to very low cross sections for producing {sup 98}Cd and {sup 102}Sn with stable beams and targets, a special detector setup utilizing NORDBALL ancillary detectors and a recoil catcher device was used. High {gamma}-ray detection efficiency was achieved with two EUROBALL Ge cluster detectors.

  5. Modification of electron states in CdTe absorber due to a buffer layer in CdTe/CdS solar cells

    Science.gov (United States)

    Fedorenko, Y. G.; Major, J. D.; Pressman, A.; Phillips, L. J.; Durose, K.

    2015-10-01

    By application of the ac admittance spectroscopy method, the defect state energy distributions were determined in CdTe incorporated in thin film solar cell structures concluded on ZnO, ZnSe, and ZnS buffer layers. Together with the Mott-Schottky analysis, the results revealed a strong modification of the defect density of states and the concentration of the uncompensated acceptors as influenced by the choice of the buffer layer. In the solar cells formed on ZnSe and ZnS, the Fermi level and the energy position of the dominant deep trap levels were observed to shift closer to the midgap of CdTe, suggesting the mid-gap states may act as recombination centers and impact the open-circuit voltage and the fill factor of the solar cells. For the deeper states, the broadening parameter was observed to increase, indicating fluctuations of the charge on a microscopic scale. Such changes can be attributed to the grain-boundary strain and the modification of the charge trapped at the grain-boundary interface states in polycrystalline CdTe.

  6. Modification of electron states in CdTe absorber due to a buffer layer in CdTe/CdS solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Fedorenko, Y. G., E-mail: y.fedorenko@liverpool.ac.uk; Major, J. D.; Pressman, A.; Phillips, L. J.; Durose, K. [Stephenson Institute for Renewable Energy and Department of Physics, School of Physical Sciences, Chadwick Building, University of Liverpool, Liverpool L69 7ZF (United Kingdom)

    2015-10-28

    By application of the ac admittance spectroscopy method, the defect state energy distributions were determined in CdTe incorporated in thin film solar cell structures concluded on ZnO, ZnSe, and ZnS buffer layers. Together with the Mott-Schottky analysis, the results revealed a strong modification of the defect density of states and the concentration of the uncompensated acceptors as influenced by the choice of the buffer layer. In the solar cells formed on ZnSe and ZnS, the Fermi level and the energy position of the dominant deep trap levels were observed to shift closer to the midgap of CdTe, suggesting the mid-gap states may act as recombination centers and impact the open-circuit voltage and the fill factor of the solar cells. For the deeper states, the broadening parameter was observed to increase, indicating fluctuations of the charge on a microscopic scale. Such changes can be attributed to the grain-boundary strain and the modification of the charge trapped at the grain-boundary interface states in polycrystalline CdTe.

  7. Annealing effects on the chemical deposited CdS films and the electrical properties of CdS/CdTe solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Han, Junfeng [State Key Laboratory of Nuclear Physics and Technology, School of Physics, Peking University, Beijing 100871 (China); Institute of Materials Science, Darmstadt University of Technology, Petersenstr. 23, 64287 Darmstadt (Germany); Liao, Cheng, E-mail: Cliao@pku.edu.cn [State Key Laboratory of Nuclear Physics and Technology, School of Physics, Peking University, Beijing 100871 (China); Jiang, Tao [State Key Laboratory of Nuclear Physics and Technology, School of Physics, Peking University, Beijing 100871 (China); Fu, Ganhua; Krishnakumar, V.; Spanheimer, C.; Haindl, G. [Institute of Materials Science, Darmstadt University of Technology, Petersenstr. 23, 64287 Darmstadt (Germany); Zhao, Kui [State Key Laboratory of Nuclear Physics and Technology, School of Physics, Peking University, Beijing 100871 (China); Klein, A.; Jaegermann, W. [Institute of Materials Science, Darmstadt University of Technology, Petersenstr. 23, 64287 Darmstadt (Germany)

    2011-02-15

    Graphical abstract: From XPS core level spectras, compared with as-depositing CdS (sample A), the Fermi level is shifting closer to the conduction band after annealing treatment in the oxygen (sample B) while it is shifting closer to the valence band after annealing treatment in the argon-hydrogen (sample C). That might be the main reason of the different performance of the final devices. The open circuit voltage of the CdS/CdTe solar cell increases when the CBD CdS is annealed with oxygen, while the performance of the solar cell decreases when the CBD CdS is annealed with argon-hydrogen. Research highlights: {yields} Two different methods (oxidation and reduction) were used to anneal CdS films for CdTe solar cells. {yields} Electrical properties were analyzed by XPS (Fermi levels of CdS films). {yields} Annealing treatment in oxidation atmosphere could shift Fermi level of CdS film to higher position and consequently improve the CdS/CdTe junction and performance of solar cells. -- Abstract: CdS layers grown by chemical bath deposition (CBD) are annealed in the oxygen and argon-hydrogen atmosphere respectively. It has been found that the open circuit voltage of the CdS/CdTe solar cell increases when the CBD CdS is annealed with oxygen before the deposition of CdTe by close spaced sublimation (CSS), while the performance of the solar cell decreases when the CBD CdS is annealed with argon-hydrogen. Electronic properties of the CdS films are investigated using X-ray photo-electron spectroscopy (XPS), which indicates that the Fermi level is shifting closer to the conduction band after annealing in the oxygen and consequently a higher open circuit voltage of the solar cell can be obtained.

  8. Single CdTe microwire photodetectors grown by close-spaced sublimation method.

    Science.gov (United States)

    Yang, Gwangseok; Kim, Byung-Jae; Kim, Donghwan; Kim, Jihyun

    2014-08-11

    We demonstrate single CdTe microwire field-effect transistors (FETs) that are highly sensitive to ultraviolet (UV) light. Dense CdTe microwires were catalytically grown using a close-spaced sublimation system. Structural, morphological and transport properties in conjunction with the optoelectronic properties were systemically investigated. CdTe microwire FETs exhibited p-type behaviors with field-effect mobilities up to 1.1 × 10(-3) cm2 V(-1) s(-1). Optoelectronic properties of our CdTe microwire FETs were studied under dark and UV-illumination conditions, where photoresponse was highly dependent on the back-gate bias conditions. Our CdTe microwire FET-based photodetectors are promising for high-performance micro-optoelectronic applications.

  9. A novel intermediate layer for Au/CdZnTe/FTO photoconductive structure

    Science.gov (United States)

    Zhang, Yuelu; Wang, Linjun; Xu, Run; Huang, Jian; Tao, Jun; Meng, Hua; Zhang, Jijun; Min, Jiahua

    2016-12-01

    In this work, graphene is tried to use to improve the performance of polycrystalline CdZnTe high-energy radiation and photon detectors. A graphene intermediate layer is prepared by spin-coating process on the surface of polycrystalline CdZnTe film, which forms a photoconductive Au/graphene/CdZnTe/FTO structure. XRD, Raman, photoelectric response and other characterisation methods are adopted to investigate the effect of graphene layer on the electrical characteristics and UV photo-response performance of CdZnTe photoconductive structure. It is demonstrated that graphene layer can significantly improve the contact property of Au/CdZnTe structure, and obviously enhance its UV photo-response and the UV sensitivity increased with one order of magnitude.

  10. NREL Collaboration Breaks 1-Volt Barrier in CdTe Solar Technology

    Energy Technology Data Exchange (ETDEWEB)

    2016-05-01

    NREL scientists have worked with Washington State University and the University of Tennessee to improve the maximum voltage available from CdTe solar cells. Changes in dopants, stoichiometry, interface design, and defect chemistry improved the CdTe conductivity and carrier lifetime by orders of magnitude, thus enabling CdTe solar cells with open-circuit voltages exceeding 1 volt for the first time. Values of current density and fill factor for CdTe solar cells are already at high levels, but sub-par voltages has been a barrier to improved efficiencies. With voltages pushed beyond 1 volt, CdTe cells have a path to produce electricity at costs less than fossil fuels.

  11. In situ compositional control of advanced HgCdTe-based IR detectors

    Science.gov (United States)

    Almeida, L. A.; Dinan, J. H.

    1999-05-01

    The application of a feedback control system for maintaining a desired compositional profile during Hg 1- xCd xTe epitaxy is reported. A spectroscopic ellipsometer monitored the optical properties of Hg 1- xCd xTe films during deposition by molecular beam epitaxy. A library of optical constants was established from in situ measurements of multiple layers of varying composition. The compositions were subsequently determined ex situ using Fourier transform infrared spectroscopy. This work represents an extension of the compositional range of this control system to measure the x-values of Hg 1- xCd xTe sensitive to long-, mid-, and short-wavelength infrared (LWIR, MWIR, and SWIR) radiation (0.16CdTe effusion cell. The application of this control system is demonstrated by measuring the compositional profile of a three layer Hg 1- xCd xTe structure suitable for use as an MWIR/SWIR detector.

  12. Large-Scale Surfactant-Free Synthesis of p-Type SnTe Nanoparticles for Thermoelectric Applications

    Directory of Open Access Journals (Sweden)

    Guang Han

    2017-02-01

    Full Text Available A facile one-pot aqueous solution method has been developed for the fast and straightforward synthesis of SnTe nanoparticles in more than ten gram quantities per batch. The synthesis involves boiling an alkaline Na2SnO2 solution and a NaHTe solution for short time scales, in which the NaOH concentration and reaction duration play vital roles in controlling the phase purity and particle size, respectively. Spark plasma sintering of the SnTe nanoparticles produces nanostructured compacts that have a comparable thermoelectric performance to bulk counterparts synthesised by more time- and energy-intensive methods. This approach, combining an energy-efficient, surfactant-free solution synthesis with spark plasma sintering, provides a simple, rapid, and inexpensive route to p-type SnTe nanostructured materials.

  13. Dependence of efficiency of thin-film CdS/CdTe solar cell on optical and recombination losses

    Science.gov (United States)

    Mohamed, H. A.

    2013-03-01

    Thin-film CdS/CdTe solar cells fabricated on glass substrates have been considered as one of the most promising candidates for large-scale applications in the field of photovoltaic energy conversion. The recorded experimental efficiency of these cells is about 16%-17% and the corresponding theoretical values are more than 28%. The main causes of efficiency loss are due to optical and recombination losses. Most of the theoretical literatures either study the effect of recombination or optical losses on the CdS/CdTe solar cell efficiency. The present work studies the effect of both the optical and recombination losses on the current density and hence the solar cell efficiency. Calculations of optical losses have been carried out based on the optical constants (refractive index and extinction coefficient) of materials used and the thickness of ITO and CdS layers. Calculation of recombination losses has been based on the values of width of space-charge region and the absorption coefficient for CdTe. It has been found that the reflection losses of the interfaces air-glass, glass-ITO, ITO-CdS, and CdS-CdTe decrease the short-circuit current (JSC) from 31.24 to 28.2 mA/cm2 (9%). The absorption losses in ITO and CdS layers decrease JSC to 22.2 (20%). The recombination losses decrease JSC to 19.7 mA/cm2 (8%). The optical and recombination losses yield efficiency of CdS/CdTe solar cells in the range of 12%-16% at thickness 100 nm of each layer of ITO and CdS. According to these results, there is a good agreement between experimental and theoretical studies and this is the real start to develop the solar cells efficiency in the future studies.

  14. Physical basis for the design of CdS/CdTe thin film solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Morales-Acevedo, Arturo [Centro de Investigacion y de Estudios Avanzados del IPN, Electrical Engineering Department, Avenida IPN No. 2508, 07360 Mexico, D.F. (Mexico)

    2006-04-14

    Solar cells based on polycrystalline semiconductor thin films have great potential for decreasing the cost of photovoltaic energy. However, this kind of solar cells has characteristics very different from those fabricated on crystalline silicon for which the carrier-transport and behavior is clearly known. Instead, for hetero-junction solar cells made on less known polycrystalline materials the design is almost empirical. In this work, several physical aspects related to the behavior of polycrystalline thin film solar cells will be discussed, and some considerations for an adequate design of this kind of solar cells will be made. For example, the recombination at the grain boundaries and its influence on the short circuit current as a function of the crystallite sizes on the active material is considered. Based on this, the appropriate thickness of each layer and their resistivity will be discussed. As an example, these considerations will be applied to CdS/CdTe heterojunction solar cells, taking into account typical properties of CdTe thin films used for solar cells. (author)

  15. Fabrication, Electrical Characterization and Simulation of Thin Film Solar Cells: CdTe and CIGS Materials

    OpenAIRE

    Es'haghi Gorji, Nima

    2014-01-01

    CdTe and Cu(In,Ga)Se2 (CIGS) thin film solar cells are fabricated, electrically characterized and modelled in this thesis. We start from the fabrication of CdTe thin film devices where the R.F. magnetron sputtering system is used to deposit the CdS/CdTe based solar cells. The chlorine post-growth treatment is modified in order to uniformly cover the cell surface and reduce the probability of pinholes and shunting pathways creation which, in turn, reduces the series resistance. The deionized wat...

  16. Improvement to thin film CdTe solar cells with controlled back surface oxidation

    OpenAIRE

    Rugen-Hankey, S.L.; Clayton, Andrew J; Barrioz, Vincent; Kartopu, Giray; Irvine, Stuart J; McGettrick, J.D.; Hammond, D.

    2015-01-01

    Thin film CdTe solar cells were produced by MOCVD, at atmospheric pressure, under a hydrogen atmosphere (i.e. oxygen-free). Window layer alloying with zinc (forming Cd1−xZnxS) and extrinsic p-type doping with arsenic (giving CdTe:As) have been used to improve photovoltaic solar cell performances, but as-grown MOCVD-CdTe PV cells are still typically characterised by low Voc (~620–690 mV). Post-deposition annealing in air for 30 min at low temperature (170 °C) prior to evaporation of the back c...

  17. Spectroscopy of low energy solar neutrinos using CdTe detectors

    Science.gov (United States)

    Zuber, K.

    2003-10-01

    The usage of a large amount of CdTe(CdZnTe) semiconductor detectors for solar neutrino spectroscopy in the low energy region is investigated. Several different coincidence signals can be formed on five different isotopes to measure the 7Be neutrino line at 862 keV in real-time. The most promising one is the usage of 116Cd resulting in 227 SNU. The presence of 125Te permits even the real-time detection of pp-neutrinos. A possible antineutrino flux above 713 keV might be detected by capture on 106Cd.

  18. Semiconductor quantum dots enhanced graphene/CdTe heterostructure solar cells by photo-induced doping

    CERN Document Server

    Li, Xiaoqiang; Wang, Peng; Xu, Zhijuan; Zhong, Huikai; Wu, Zhiqian; Lin, Shisheng

    2015-01-01

    Photo-induced doping is employed into graphene based solar cell through designing of a novel type of solar cell based on graphene/CdTe Schottky heterostructure. By coating a layer of ultrathin CdSe quantum dots onto graphene/CdTe heterostructure, the performance of the graphene/CdTe solar cell is improved by about 50%. Photo-induced doping is mainly accounted for this enhancement, as evidenced by resistance, photoluminescence and quantum efficiency measurements. This work demonstrates a general and feasible way of designing novel type of solar cells based on two dimensional materials/semiconductor heterostructures.

  19. Effect of Sn doping on nonlinear optical properties of quaternary Se-Sn-(Bi,Te) chalcogenide thin films

    Science.gov (United States)

    Yadav, Preeti; Sharma, Ambika

    2015-08-01

    The aim of this work is to report the effect of Sn doping on the third order nonlinear optical properties of chalcogenide Se84-xTe15Bi1.0Snx thin films. Melt quenching technique has been used for the preparation of bulk chalcogenide glasses. Thin films of the studied composition are deposited on cleaned glass substrate by thermal evaporation technique. Optical band gap (Eg) is calculated by using Tauc extrapolation method and is found to increase from 1.27 eV to 1.64 eV with the incorporation of Sn content. Stryland approach is utilized for the calculation of two photon absorption coefficient (β2). The nonlinear refractive index (n2) and third order susceptibility (χ(3) are calculated using Tichy and Ticha approach. The result shows that nonlinear refractive index (n2) follows the same trend as that of linear refractive index (n). The values of n2 of studied composition as compared to pure silica are 1000-5000 times higher.

  20. Real-time observation of nanoscale topological transitions in epitaxial PbTe/CdTe heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Groiss, H., E-mail: heiko.groiss@jku.at, E-mail: istvan.daruka@jku.at; Daruka, I., E-mail: heiko.groiss@jku.at, E-mail: istvan.daruka@jku.at; Springholz, G.; Schäffler, F. [Institute of Semiconductor and Solid State Physics, Johannes Kepler University, Linz 4040 (Austria); Koike, K.; Yano, M. [Nanomaterials Microdevices Research Center, Osaka Institute of Technology, Asahi-ku Ohmiya, Osaka 535-8585 (Japan); Hesser, G. [Center for Surface- and Nanoanalytics (ZONA), Johannes Kepler University, Linz 4040 (Austria); Zakharov, N.; Werner, P. [Max Planck Institute of Microstructure Physics, Halle 06120 (Germany)

    2014-01-01

    The almost completely immiscible PbTe/CdTe heterostructure has recently become a prototype system for self-organized quantum dot formation based on solid-state phase separation. Here, we study by real-time transmission electron microscopy the topological transformations of two-dimensional PbTe-epilayers into, first, a quasi-one-dimensional percolation network and subsequently into zero-dimensional quantum dots. Finally, the dot size distribution coarsens by Ostwald ripening. The whole transformation sequence occurs during all stages in the fully coherent solid state by bulk diffusion. A model based on the numerical solution of the Cahn-Hilliard equation reproduces all relevant morphological and dynamic aspects of the experiments, demonstrating that this standard continuum approach applies to coherent solids down to nanometer dimensions. As the Cahn-Hilliard equation does not depend on atomistic details, the observed morphological transformations are general features of the model. To confirm the topological nature of the observed shape transitions, we developed a parameter-free geometric model. This, together with the Cahn-Hilliard approach, is in qualitative agreement with the experiments.

  1. Real-time observation of nanoscale topological transitions in epitaxial PbTe/CdTe heterostructures

    Directory of Open Access Journals (Sweden)

    H. Groiss

    2014-01-01

    Full Text Available The almost completely immiscible PbTe/CdTe heterostructure has recently become a prototype system for self-organized quantum dot formation based on solid-state phase separation. Here, we study by real-time transmission electron microscopy the topological transformations of two-dimensional PbTe-epilayers into, first, a quasi-one-dimensional percolation network and subsequently into zero-dimensional quantum dots. Finally, the dot size distribution coarsens by Ostwald ripening. The whole transformation sequence occurs during all stages in the fully coherent solid state by bulk diffusion. A model based on the numerical solution of the Cahn-Hilliard equation reproduces all relevant morphological and dynamic aspects of the experiments, demonstrating that this standard continuum approach applies to coherent solids down to nanometer dimensions. As the Cahn-Hilliard equation does not depend on atomistic details, the observed morphological transformations are general features of the model. To confirm the topological nature of the observed shape transitions, we developed a parameter-free geometric model. This, together with the Cahn-Hilliard approach, is in qualitative agreement with the experiments.

  2. CdS and CdTeS quantum dot decorated TiO{sub 2} nanowires. Synthesis and photoefficiency

    Energy Technology Data Exchange (ETDEWEB)

    Medina-Gonzalez, Yaocihuatl; Xu, William Z; Chen Bo; Farhanghi, Nasrin; Charpentier, Paul A, E-mail: ymedina@uwo.ca, E-mail: pcharpentier@eng.uwo.ca [Department of Chemical and Biochemical Engineering, Faculty of Engineering, University of Western Ontario, London, ON, N6A 5B9 (Canada)

    2011-02-11

    An easy process was developed to synthesize TiO{sub 2} nanowires sensitized with CdS and CdTeS quantum dots (QDs) requiring no pretreatment of the TiO{sub 2} nanowires prior to nanoparticle generation. CdS and CdTeS nanoparticles were firstly grown by an in situ colloidal method directly onto the TiO{sub 2} surface, hence not requiring subsequent functionalization of the QDs. The resulting nanostructure assembly and composition was confirmed by transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Successful decoration of the TiO{sub 2} nanowires by the QDs was observed by TEM, while XPS spectra provided clear evidence for the coexistence of CdS and CdTeS QDs and TiO{sub 2} nanowires. The electronic structure of the TiO{sub 2} nanowires was preserved as indicated by Raman spectroscopy. Preliminary photocurrent measurements showed that inclusion of Te in CdS QDs improved the photocurrent efficiency. Compared to bare TiO{sub 2} nanowires, CdS/TiO{sub 2} nanoassemblies showed an enhancement in photocurrent efficiency of 300% while CdTeS/TiO{sub 2} presented an improvement of 350%. This study indicates that the generation of strongly anchored CdS and CdTeS QDs on a TiO{sub 2} nanowire surface is achievable without introduction of a linker molecule, whose presence is known to decrease the electron injection efficiency.

  3. Using a CdTe detector for 125Te Mössbauer Spectroscopy: Application to the f-factor in Mg3TeO6

    Science.gov (United States)

    Bargholtz, Chr; Blomquist, J.; Fumero, E.; Mårtensson, L.; Einarsson, L.; Wäppling, R.

    2000-09-01

    An apparatus for Mössbauer spectroscopy has been developed with a cadmium telluride (CdTe) γ-ray detector. Complete data regarding γ-ray energy, source velocity, temperature and real time are stored for off-line analysis. The apparatus has been used to study the spectrum of 125Te in Mg 3TeO 6 at room temperature. The 35.5 keV transition of 125Te in Mg 3TeO 6 was found to have a recoil-free fraction f=0.392(5) corresponding to a Debye temperature θ=352(3) K.

  4. MBE Growth and Transfer of HgCdTe Epitaxial Films from InSb Substrates

    Science.gov (United States)

    de Lyon, T. J.; Rajavel, R. D.; Nosho, B. Z.; Terterian, S.; Beliciu, M. L.; Patterson, P. R.; Chang, D. T.; Boag-O'Brien, M. F.; Holden, B. T.; Jacobs, R. N.; Benson, J. D.

    2010-07-01

    An investigation of the heteroepitaxial growth of HgCdTe films onto InSb(211)B substrates is reported. High-quality HgCdTe(211)B single-crystal films have been successfully deposited onto InSb(211)B substrates and have been characterized with x-ray diffraction rocking curve analysis, etch pit density analysis, and surface void defect mapping. X-ray rocking curve (422) reflection full-width at half-maximum of 60 arcsec has been obtained for 7- μm-thick x = 0.22 HgCdTe epitaxial films, and etch pit densities of 3 × 106 cm-2 to 3 × 107 cm-2 have been observed. A significant reduction in HgCdTe void defect densities to 100 cm-2 to 200 cm-2 has been observed on InSb, including a complete absence of large “void cluster” defects that are often observed for growth on CdZnTe. Wafer bow induced by the growth of HgCdTe on InSb is less than 1 μm for 2-inch-diameter substrates. Significant diffusion of In into HgCdTe is observed for HgCdTe/InSb wafers that are subjected to Hg anneals at 250°C to 300°C. A preliminary investigation of the transfer of HgCdTe films from InSb onto Si substrates has also been undertaken, using an adhesive wafer bonding approach evaluated with scanning acoustic microscopy. The infrared transmission characteristics of the bonding adhesive have been investigated with respect to postgrowth annealing procedures to establish the compatibility of the bonding approach with HgCdTe device processing and detector operation.

  5. Translocation and neurotoxicity of CdTe quantum dots in RMEs motor neurons in nematode Caenorhabditis elegans

    Energy Technology Data Exchange (ETDEWEB)

    Zhao, Yunli; Wang, Xiong; Wu, Qiuli; Li, Yiping; Wang, Dayong, E-mail: dayongw@seu.edu.cn

    2015-02-11

    Graphical abstract: - Highlights: • We investigated in vivo neurotoxicity of CdTe QDs on RMEs motor neurons in C. elegans. • CdTe QDs in the range of μg/L caused neurotoxicity on RMEs motor neurons. • Bioavailability of CdTe QDs may be the primary inducer for CdTe QDs neurotoxicity. • Both oxidative stress and cell identity regulate the CdTe QDs neurotoxicity. • CdTe QDs were translocated and deposited into RMEs motor neurons. - Abstract: We employed Caenorhabditis elegans assay system to investigate in vivo neurotoxicity of CdTe quantum dots (QDs) on RMEs motor neurons, which are involved in controlling foraging behavior, and the underlying mechanism of such neurotoxicity. After prolonged exposure to 0.1–1 μg/L of CdTe QDs, abnormal foraging behavior and deficits in development of RMEs motor neurons were observed. The observed neurotoxicity from CdTe QDs on RMEs motor neurons might be not due to released Cd{sup 2+}. Overexpression of genes encoding Mn-SODs or unc-30 gene controlling cell identity of RMEs neurons prevented neurotoxic effects of CdTe QDs on RMEs motor neurons, suggesting the crucial roles of oxidative stress and cell identity in regulating CdTe QDs neurotoxicity. In nematodes, CdTe QDs could be translocated through intestinal barrier and be deposited in RMEs motor neurons. In contrast, CdTe@ZnS QDs could not be translocated into RMEs motor neurons and therefore, could only moderately accumulated in intestinal cells, suggesting that ZnS coating might reduce neurotoxicity of CdTe QDs on RMEs motor neurons. Therefore, the combinational effects of oxidative stress, cell identity, and bioavailability may contribute greatly to the mechanism of CdTe QDs neurotoxicity on RMEs motor neurons. Our results provide insights into understanding the potential risks of CdTe QDs on the development and function of nervous systems in animals.

  6. Electro-Plating and Characterisation of CdTe Thin Films Using CdCl2 as the Cadmium Source

    OpenAIRE

    Nor A. Abdul-Manaf; Hussein I. Salim; Mohammad L. Madugu; Olajide I. Olusola; Imyhamy M. Dharmadasa

    2015-01-01

    Cadmium telluride (CdTe) thin films have been successfully prepared from an aqueous electrolyte bath containing cadmium chloride (CdCl2)·H2O and tellurium dioxide (TeO2) using an electrodeposition technique. The structural, electrical, morphological and optical properties of these thin films have been characterised using X-ray diffraction (XRD), Raman spectroscopy, optical profilometry, DC current-voltage (I-V) measurements, photoelectrochemical (PEC) cell measurement, scanning electron micr...

  7. Stepwise cooling technique as a method of growing high-perfection Cl-compensated CdTe

    Science.gov (United States)

    Pavlyuk, M. D.; Subbotin, I. A.; Kanevsky, V. M.; Artemov, V. V.

    2017-01-01

    High-perfection crystals of Cl-compensated CdTe have been grown by the Obreimov-Shubnikov technique using a schedule of stepwise crystal cooling developed with due regard for the correct CdTe phase diagram.

  8. Micro through nanostructure investigations of polycrystalline CdTe: Correlations with processing and electronic structures

    Energy Technology Data Exchange (ETDEWEB)

    Levi, D.H.; Moutinho, H.R.; Hasoon, F.A.; Keyes, B.M.; Ahrenkiel, R.K.; Al-Jassim, M.; Kazmerski, L.L. [National Renewable Energy Lab., Golden, CO (United States); Birkmire, R.W. [Univ. of Delaware, Newark, DE (United States). Inst. of Energy Conversion

    1994-12-31

    This paper provides first-time correlations of the nanoscale physical structure with the macroscale electronic and optical properties of CdTe/CdS thin films for several standard deposition techniques. Atomic force microscopy (AFM) was used to determine the micro and nanostructures of polycrystalline CdTe thin films used in photovoltaic (PV) cell fabrication. Photoluminescence (PL) was used to determine band gap, relative defect density, and photoexcited carrier lifetime. Nanostructural features (nanograins), beyond the spatial resolution of conventional scanning electron microscopy (SEM), were observed and characterized in as-deposited CdTe. The correlations of the proximal probe measurements of the physical structure with the optically determined electronic properties were used to show the effects of the chemical and heat processing, directly and conclusively. A particularly striking effect with important implications for PV applications is the diffusion of sulfur across the CdTe/CdS interface during heat treatment.

  9. Carrier density and lifetime for different dopants in single-crystal and polycrystalline CdTe

    Science.gov (United States)

    Burst, James M.; Farrell, Stuart B.; Albin, David S.; Colegrove, Eric; Reese, Matthew O.; Duenow, Joel N.; Kuciauskas, Darius; Metzger, Wyatt K.

    2016-11-01

    CdTe defect chemistry is adjusted by annealing samples with excess Cd or Te vapor with and without extrinsic dopants. We observe that Group I (Cu and Na) elements can increase hole density above 1016 cm-3, but compromise lifetime and stability. By post-deposition incorporation of a Group V dopant (P) in a Cd-rich ambient, lifetimes of 30 ns with 1016 cm-3 hole density are achieved in single-crystal and polycrystalline CdTe without CdCl2 or Cu. Furthermore, phosphorus doping appears to be thermally stable. This combination of long lifetime, high carrier concentration, and improved stability can help overcome historic barriers for CdTe solar cell development.

  10. Carrier density and lifetime for different dopants in single-crystal and polycrystalline CdTe

    Directory of Open Access Journals (Sweden)

    James M. Burst

    2016-11-01

    Full Text Available CdTe defect chemistry is adjusted by annealing samples with excess Cd or Te vapor with and without extrinsic dopants. We observe that Group I (Cu and Na elements can increase hole density above 1016 cm−3, but compromise lifetime and stability. By post-deposition incorporation of a Group V dopant (P in a Cd-rich ambient, lifetimes of 30 ns with 1016 cm−3 hole density are achieved in single-crystal and polycrystalline CdTe without CdCl2 or Cu. Furthermore, phosphorus doping appears to be thermally stable. This combination of long lifetime, high carrier concentration, and improved stability can help overcome historic barriers for CdTe solar cell development.

  11. Highly luminescent hybrid SiO2-coated CdTe quantum dots: synthesis and properties.

    Science.gov (United States)

    Liu, Ning; Yang, Ping

    2013-01-01

    Novel hybrid SiO2-coated CdTe quantum dots (QDs) were created using CdTe QDs coated with a hybrid SiO2 shell containing Cd(2+) ions and a sulfur source via a sol-gel process in aqueous solution. Aqueous CdTe QDs with tunable emitting color created through a reaction between cadmium chloride and sodium hydrogen telluride was used as cores for the preparation of hybrid SiO2-coated CdTe QDs. In our experiments we found that the surface state of the cores and preparation conditions that affect the formation of the hybrid SiO2 shell also greatly affect photoluminescence of the hybrid SiO2-coated CdTe QDs. The generation of CdS-like clusters in the vicinity of the CdTe QDs, caused the quantum size effect of the QDs to be greatly reduced, which changes photoluminescence properties of the hybrid QDs fundamentally. Namely, the novel hybrid SiO2 shell played an important role in generating a series of specific optical properties. In addition, the novel hybrid SiO2 shell can be created if no CdTe QD is added. In order to gain an insight into the inter structure of the hybrid shell, we characterized the hybrid SiO2-coated CdTe QDs using X-ray diffraction analysis and discuss the formation mechanism of such a hybrid structure. This work is significant because the novel hybrid SiO2-coated CdTe QDs with its excellent properties can be used in many applications, such as biolabeling and optoelectronic devices.

  12. Synthesis, Structural and Optical Characterization of CdTeSe/ZnSe and CdTeSe/ZnTe Core/Shell Ternary Quantum Dots for Potential Application in Solar Cells

    OpenAIRE

    Hung, Le Xuan; Thang, Pham Nam; Van Nong, Hoang; Yen, Nguyen Hai; Chinh, Vu Đuc; Van Vu, Le; Hien, Nguyen Thi Thuc; Marcillac, Willy Daney,; Hong, Phan Ngoc; Loan, Nguyen Thu; Schwob, Catherine; Maître, Agnès; Liem, Nguyen Quang; Bénalloul, Paul; Coolen, Laurent

    2016-01-01

    International audience; This work presents the results on the fabrication, structural and optical properties of CdTeSe/ZnTe and CdTeSe/ZnSe n monolayers (ML) (with n = 0,1,2,4 and 6 being the nominal shell monolayer thickness) ternary alloyed core/shell quantum dots (QDs). Transmission electron microscopy has been used to observe the shape and size of the QDs. These QDs crystallize at the zinc-blende phase. Raman scattering has been used to characterize the CdTeSe QDs’ alloy composition in th...

  13. SCAPS Modeling for Degradation of Ultrathin CdTe Films: Materials Interdiffusion

    Science.gov (United States)

    Houshmand, Mohammad; Zandi, M. Hossein; Gorji, Nima E.

    2015-09-01

    Ultrathin film solar cells based on CdS/CdTe ( d CdTe ≤ 1 µm) suffer from two main issues: incomplete photo absorption and high degradation rate. The former is cured by light-trapping techniques, whereas the latter is a matter of fabrication details. Interdiffusion of the material components and formation of subsequent interlayers at the front/back region can change the optical/electrical properties and performance/stability of the device. We model the degradation of the ultrathin CdTe film devices considering the material interdiffusion and interlayers formation: CdTeS, CdZnTe, Cu x Te (i.e., Te/Cu bilayer), and oxide interlayers (i.e., CdTeO3). The diffusion rate of the materials is considered separately and the reactions that change the interlayer's properties are studied. Additionally, a back contact of single-walled carbon nanotube showed a higher stability than the metallic contacts. A new time-dependent approach is applied to simulate the degradation rate due to formation of any interlayer. It is shown that the materials interdiffusion causes a defect increment under thermal stress and illumination. The metallic back contact accelerates the degradation, whereas single-walled carbon nanotubes show the highest stability. A SCAPS simulator was used because of its ability in defining the properties of the back contact and metastabilities at the interface layers. The properties of the layers were taken from the experimental data reported in the literature.

  14. Minority carrier lifetimes in different doped LWIR HgCdTe grown by LPE

    Science.gov (United States)

    Qiu, GuangYin; Wei, YanFeng; Sun, QuanZhi; Yang, JianRong

    2012-10-01

    The carrier lifetimes of different types of p-type doped HgCdTe(x~0.23) long wavelength infrared (LWIR) epilayers were measured which were Hg-vacancy, Au and arsenic doped ones prepared by Te-rich Liquid-phase epitaxy (LPE). By comparing the lifetimes of Hg-vacancy and extrinsic doped HgCdTe, we focus on three primary mechanisms limiting the lifetimes in these different p-type HgCdTe samples: radiative recombination, Auger recombination and Schokley-Read- Hall (SRH) Recombination. The recombination mechanism in p-type HgCdTe is the SRH recombination at low temperatures and Auger and radiative recombination at high temperature. It is found that the lifetime of As-doped and Au-doped HgCdTe is far longer than that of Hg-vacancy-doped sample which is caused by the deep energy level of the Hg-vacancy acceptor that is considered as a recombination center in HgCdTe. Also we found lifetime in those p-type doped HgCdTe LWIR epilayers is limited by SRH by comparing the experimental lifetimes with the calculated data. Impurity doping was found to have a main effect on minority carrier lifetime.

  15. Yb-doped SnTe semimetal thin films deposited by thermal evaporation: Structural, electrical, and thermoelectric properties

    Science.gov (United States)

    Hmood, A.; Kadhim, A.; Hassam, H. A.

    2014-12-01

    Sn monochalcogenide and Yb-doped Sn1-xYbxTe (0.0 ⩾ x ⩽ 0.1) semimetals, which are known for their usefulness as efficient thermoelectric (TE) materials, were prepared by solid-state microwave technique. Polycrystalline thin films of Sn1-xYbxTe were deposited onto clean glass substrates by using vacuum evaporation technique at 10-6 bar. The structures of the polycrystalline thin films were examined by X-ray diffraction patterns. A rock salt structure was observed. Grain size increased with increasing Yb content but not according to a sequence. The morphology of the nanosheet structures for these thin films was determined by field emission scanning electron microscopy. TE properties were measured at a temperature range of 298-523 K. The carrier concentrations of the films were determined by Hall effect measurements at 300 K.

  16. Surface structure of CdS layer at the interface of CdS-SnO2 junction and the diagram of surface states

    Science.gov (United States)

    Caraman, I.; Lazar, I.; Caraman, M.; Rusu, D.

    2009-01-01

    The SnO2-CdS type structures with SnO2 film deposited by thermal pirolize in SnCl4-etanol solution were obtained. The CdS film with submicron thickness was obtained in cvasiclosed volume. The transversal section of the SnO2-CdS junction as well as the outer surface of the CdS film was analyzed using the electronic microscope. The density of the crystallization germs in the CdS film was about 1013cm-2. The luminescence spectrum of CdS has been examined. The existence of exciton line (n=1) in reflection and emission spectrum serves as a criteria of crystalline perfection of surface film.

  17. Improved Performance of CdS/CdTe Quantum Dot-Sensitized Solar Cells Incorporating Single-Walled Carbon Nanotubes

    Energy Technology Data Exchange (ETDEWEB)

    Shin, Ho Kyeong; Park, Tae Hee; Lee, Jun Young; Yang, Jong Hee; Han, Jin Wook; Yi, Whi Kun [Hanyang University, Seoul (Korea, Republic of)

    2014-09-15

    We fabricated quantum dot-sensitized solar cells (QDSSCs) using cadmium sulfide (CdS) and cadmium telluride (CdTe) quantum dots (QDs) as sensitizers. A spin coated TiO{sub 2} nanoparticle (NP) film on tin-doped indium oxide glass and sputtered Au on fluorine-doped tin oxide glass were used as photo-anode and counter electrode, respectively. CdS QDs were deposited onto the mesoporous TiO{sub 2} layer by a successive ionic layer adsorption and reaction method. Pre-synthesized CdTe QDs were deposited onto a layer of CdS QDs using a direct adsorption technique. CdS/CdTe QDSSCs had high light harvesting ability compared with CdS or CdTe QDSSCs. QDSSCs incorporating single-walled carbon nanotubes (SWNTs), sprayed onto the substrate before deposition of the next layer or mixed with TiO{sub 2} NPs, mostly exhibited enhanced photo cell efficiency compared with the pristine cell. In particular, a maximum rate increase of 24% was obtained with the solar cell containing a TiO{sub 2} layer mixed with SWNTs.

  18. CdTe-JA 偶合物的制备和应用%Coupling Reaction and Application of Jasmonic Acid and CdTe Quantum Dots

    Institute of Scientific and Technical Information of China (English)

    高艳红; 王玉洁; 何桂; 俞英

    2014-01-01

    As a good luminescent material , quantum dots can be a probe for targets in complicated system through the surface modification with recognition function molecule .CdTe quantum dots ( QDs) were synthesized in aque-ous solution using mercaptoethylamine ( MA) as stabilizer .The optimal conditions for synthesis were studied by flu-orescence spectroscopy .The purification of CdTe QDs with different solvents and pH values of buffer solution was investigated systematically .The results showed that the purification with twice volume isopropanol was the best . The fluorescence of QDs basically unchanged in pH 7.4 buffer solution .The jasmonic acid-CdTe conjugates was obtained by coupling CdTe QDs with jasmonic acid ( JA) using the N-hydroxysuccinimide ( NHS) as a coupling a-gent.The optimal conditions for coupling reaction are pH 7.4 and stiring for 30 min at 37 ℃.After the JA mole-cule linked with CdTe QDs , the maximum absorption peak of jasmonic acid-CdTe conjugates was blue-shifted by 10 nm.The photostability of jasmonic acid-CdTe conjugates was also studied by fluorescence microscope .The jasmon-ic acid-CdTe conjugates was applied preliminarily in the labeling of root sections of mung bean seedlings .%以巯基乙胺( MA)作为修饰剂,在水相条件下合成了稳定的CdTe量子点,优化了合成反应条件;其中用异丙醇做沉淀剂效果好,量子点重新分散到pH值为7.4的Tris-HCl缓冲溶液中,荧光基本保持不变;用N-羟基琥珀酰亚胺(NHS)作偶联剂,量子点与茉莉酸(JA)在pH值为7.4,37℃反应30 min合成了具有识别茉莉酸结合位点的探针. CdTe-JA最大吸收峰与CdTe相比蓝移了约10 nm,抗光漂白性好,并初步对绿豆幼苗根部进行了荧光标记.

  19. Correlation of stability to varied CdCl2 treatment and related defects in CdS/CdTe PV devices as measured by thermal admittance spectroscopy

    Science.gov (United States)

    Enzenroth, R. Albert; Barth, K. L.; Sampath, W. S.

    2005-11-01

    A correlation between the CdCl2 treatment and the change in conversion efficiency with light and heat stress indoors (stability) has been shown previously by our group for CdS/CdTe:Cu PV devices. In the present work CdTe devices were fabricated with various CdCl2 treatments and with and without a Cu containing back contact. The electrical characteristics of the defects acting as traps in these devices were studied using thermal admittance spectroscopy (TAS). The activation energy Et-EV, the apparent capture cross section and the densities of state functions (using Walter's method) of the traps in the devices were estimated.

  20. CdTe介质膜与HgCdTe晶片间界面特性的研究%STUDY OF THE INTERFACE OF THE SPUTTERING CdTe DIELECTRIC FILM AND HgCdTe CRYSTAL

    Institute of Scientific and Technical Information of China (English)

    周咏东; 赵军; 李言谨; 方家熊

    2000-01-01

    利用Ar+束溅射沉积技术在HgCdTe表面低温生长了CdTe介质薄膜.分别用CdTe介质膜和HgCdTe自身阳极氧化膜对HgCdTe表面钝化.利用光电导衰退信号波形的拟合,得到了不同表面钝化的HgCdTe非平衡载流子表面复合速度.结果表明,CdTe/HgCdTe界面质量已超过自身阳极氧化膜/HgCdTe界面质量.

  1. [Preparation and spectral characterization of CdS(y)Te(1-y) thin films].

    Science.gov (United States)

    Li, Wei; Feng, Liang-Huan; Wu, Li-Li; Zhang, Jing-Quan; Li, Bing; Lei, Zhi; Cai, Ya-Ping; Zheng, Jia-Gui; Cai, Wei; Zhang, Dong-Min

    2008-03-01

    CdS(y)Te(1-y) (0 thin films were prepared on glass substrates by co-evaporation of powders of CdTe and CdS. For the characterization of the structure and composition of the CdS(y)Te(1-y) thin films the X-ray diffraction (XRD) and energy-dispersive spectroscopy (EDS) were used. The results indicate that the values of sulfur content y detected and controlled by the quartz wafer detector show good agreement with the EDS results. The films were found to be cubic for x or = 0.3. The 20-50 nm of grain sizes for CdS(y)Te(1-y) thin films were calculated using a method of XRD analysis. Finally, the optical properties of CdS(y)Te(1-y) thin films were characterized by UV-Vis-NIR spectroscopy alone. According to a method from Swanepoel, together with the first-order Sellmeier model, the thickness, of d-535 nm, energy gap of E(g)-1.41 eV, absorption coefficient, alpha(lambda) and refractive index, n(lambda) of CdS(0.22) Te(0.78) thin films were determined from the transmittance at normal incidence of light in the wavelength range 300-2 500 nm. The results also indicate that the CdS(y)Te(1-y) thin films with any composition (0 thin films can be implemented for other semiconductor thin films.

  2. Study of Cu-related Defect States in Single-crystal CdTe

    Science.gov (United States)

    Corwine, Caroline; Sites, James; Gessert, Timothy; Metzger, Wyatt; Dippo, Pat; Duda, Anna

    2003-10-01

    We have studied single-crystal CdTe using low-temperature photoluminescence (PL) in an effort to understand the effects of copper on the deep levels, as well as the effect of a bromine methanol (BrMe) etch on subsequent copper diffusion into CdTe. In present polycrystalline CdS/CdTe solar cell technology, the use of a back contact that contains Cu is necessary to produce high-efficiency cells. However, it is not generally understood why Cu is necessary for these devices to function well. In order to obtain further advances in the efficiencies of these solar cells, it is important to know how the back contact process may affect the defect states in CdTe. PL is one tool used to study defect states. However, before PL can be used effectively for polycrystalline CdTe solar cells, relevant spectral features first must be interpreted for single-crystal CdTe. All PL in this study was taken at 4.5 K. We report on PL peaks at 1.40 and 1.45 eV, which are seen only after Cu is diffused into single-crystal CdTe.

  3. Spectroscopic and electrochemical monitoring of band structure changes during the alloying of CdTe QDs by Hg2+ ions

    Science.gov (United States)

    Tynkevych, Olena O.; Ranoszek-Soliwoda, Katarzyna; Grobelny, Jaroslaw; Selyshchev, Oleksandr V.; Khalavka, Yuriy B.

    2016-10-01

    The series of ultrasmall thioglycolic acid-stabilized colloidal Cd1-x Hg x Te QDs (with d ≈ 2.3 nm) with different % Hg2+ content were synthesized by an ion-exchange reaction in water solution. The resulting Cd1-x Hg x Te QDs were characterized using UV-vis absorption and photoluminescent optical spectroscopic studies, cyclic voltammetry and scanning transmission electron microscopy. By comparison of the results from different methods we conclude that Hg-alloying occurs in three stages—with the formation of three different types of QDs structures, namely core/shell CdTe/Cd1-x Hg x Te QDs, core/shell/shell CdTe/Cd1-x Hg x Te/CdHg QDs and core/shell Cd1-x Hg x Te/CdHg QDs.

  4. Zinc segregation in CdZnTe grown under Cd/Zn partial pressure control

    Science.gov (United States)

    Azoulay, M.; Rotter, S.; Gafni, G.; Tenne, R.; Roth, M.

    1992-02-01

    CdZnTe crystals have been grown by the modified vertical gradient freeze (VGF) method. Growth atmosphere control has been introduced to compensate for the Zn depletion in the melt during solidification. The axial Zn concentration in the grown crystals is found to be uniform within ±3%, as evaluated by X-ray diffraction and electron microprobe analysis. The radial segregation of Zn is minimal and does not exceed the experimental error due to the nearly planar interface achieved. Zinc microsegregation has been studied as well and is discussed in terms of the temporal variations of the solute concentration at the growth interface.

  5. Formation of nanoscale spatially indirect excitons: Evolution of the type-II optical character of CdTe/CdSe heteronanocrystals

    NARCIS (Netherlands)

    de Mello Donega, C.

    2010-01-01

    In this work, the evolution of the optical properties of nanoscale spatially indirect excitons as a function of the size, shape, and composition of the heteronanostructure is investigated, using colloidal CdTe/CdSe heteronanocrystals (2.6 nm diameter CdTe core and increasing CdSe volume fraction) as

  6. CdTe-CdS solar cells - Production in a new baseline and investigation of material properties

    Energy Technology Data Exchange (ETDEWEB)

    Haedrich, M. [Institut fuer Festkoerperphysik, Friedrich-Schiller-Universitaet Jena, Max-Wien-Platz 1, 07743 Jena (Germany)]. E-mail: mathias.haedrich@uni-jena.de; Lorenz, N. [Institut fuer Festkoerperphysik, Friedrich-Schiller-Universitaet Jena, Max-Wien-Platz 1, 07743 Jena (Germany); Metzner, H. [Institut fuer Festkoerperphysik, Friedrich-Schiller-Universitaet Jena, Max-Wien-Platz 1, 07743 Jena (Germany); Reisloehner, U. [Institut fuer Festkoerperphysik, Friedrich-Schiller-Universitaet Jena, Max-Wien-Platz 1, 07743 Jena (Germany); Mack, S. [Institut fuer Festkoerperphysik, Friedrich-Schiller-Universitaet Jena, Max-Wien-Platz 1, 07743 Jena (Germany); Gossla, M. [Institut fuer Festkoerperphysik, Friedrich-Schiller-Universitaet Jena, Max-Wien-Platz 1, 07743 Jena (Germany); Witthuhn, W. [Institut fuer Festkoerperphysik, Friedrich-Schiller-Universitaet Jena, Max-Wien-Platz 1, 07743 Jena (Germany)

    2007-05-31

    In this paper, we describe our new baseline for CSS-CdTe-CdS solar cells on 10 x 10 cm{sup 2} substrates. The deposition of the p-n junction and all the following steps were performed at the Institut fuer Festkoerperphysik (IFK) in Jena. Using the new baseline, we are already able to produce solar cells with similar properties as commercial ones. In the batch type process, all manufacturing steps can be investigated separately. We employ Rutherford backscattering spectrometry (RBS), X-ray diffraction (XRD) and external quantum efficiency (EQE) measurements to characterise the structure of the bulk materials and interfaces. It is demonstrated that by RBS the front contact becomes accessible for thinned CdTe films. At the back contact, RBS spectra show a tellurium accumulation which is due to etching. This tellurium rich layer is confirmed by XRD with Rietveld refinement. The intermixing at the CdS-CdTe interface caused by the activation step is quantified by a bandgap determination based on EQE measurements. From the bandgap energy of the CdTe{sub 1-x}S{sub x} compound, we calculated the sulphur fraction x at the interface. XRD measurements imply that the activation step induces a (111) texture in CdTe. With regard to an improved manufacturing process, our cells are compared to industrial cells produced by Antec Solar Energy.

  7. CdTe and CdSe Quantum Dots Cytotoxicity: A Comparative Study on Microorganisms

    Science.gov (United States)

    Gomes, Suzete A.O.; Vieira, Cecilia Stahl; Almeida, Diogo B.; Santos-Mallet, Jacenir R.; Menna-Barreto, Rubem F. S.; Cesar, Carlos L.; Feder, Denise

    2011-01-01

    Quantum dots (QDs) are colloidal semiconductor nanocrystals of a few nanometers in diameter, being their size and shape controlled during the synthesis. They are synthesized from atoms of group II–VI or III–V of the periodic table, such as cadmium telluride (CdTe) or cadmium selenium (CdSe) forming nanoparticles with fluorescent characteristics superior to current fluorophores. The excellent optical characteristics of quantum dots make them applied widely in the field of life sciences. Cellular uptake of QDs, location and translocation as well as any biological consequence, such as cytotoxicity, stimulated a lot of scientific research in this area. Several studies pointed to the cytotoxic effect against micoorganisms. In this mini-review, we overviewed the synthesis and optical properties of QDs, and its advantages and bioapplications in the studies about microorganisms such as protozoa, bacteria, fungi and virus. PMID:22247686

  8. Core-shell ITO/ZnO/CdS/CdTe nanowire solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Williams, B. L.; Phillips, L.; Major, J. D.; Durose, K. [Stephenson Institute for Renewable Energy, University of Liverpool, Chadwick Building, Peach St., Liverpool L69 7ZF (United Kingdom); Taylor, A. A.; Mendis, B. G.; Bowen, L. [G. J. Russell Microscopy Facility, University of Durham, South Road, Durham DH1 3LE (United Kingdom)

    2014-02-03

    Radial p-n junction nanowire (NW) solar cells with high densities of CdTe NWs coated with indium tin oxide (ITO)/ZnO/CdS triple shells were grown with excellent heterointerfaces. The optical reflectance of the devices was lower than for equivalent planar films by a factor of 100. The best efficiency for the NW solar cells was η = 2.49%, with current transport being dominated by recombination, and the conversion efficiencies being limited by a back contact barrier (ϕ{sub B} = 0.52 eV) and low shunt resistances (R{sub SH} < 500 Ω·cm{sup 2})

  9. CdTe and CdSe Quantum Dots Cytotoxicity: A Comparative Study on Microorganisms

    Directory of Open Access Journals (Sweden)

    Denise Feder

    2011-12-01

    Full Text Available Quantum dots (QDs are colloidal semiconductor nanocrystals of a few nanometers in diameter, being their size and shape controlled during the synthesis. They are synthesized from atoms of group II–VI or III–V of the periodic table, such as cadmium telluride (CdTe or cadmium selenium (CdSe forming nanoparticles with fluorescent characteristics superior to current fluorophores. The excellent optical characteristics of quantum dots make them applied widely in the field of life sciences. Cellular uptake of QDs, location and translocation as well as any biological consequence, such as cytotoxicity, stimulated a lot of scientific research in this area. Several studies pointed to the cytotoxic effect against micoorganisms. In this mini-review, we overviewed the synthesis and optical properties of QDs, and its advantages and bioapplications in the studies about microorganisms such as protozoa, bacteria, fungi and virus.

  10. A Comprehensive Study on Mo/CdTe Metal-Semiconductor Interface Deposited by Radio Frequency Magnetron Sputtering.

    Science.gov (United States)

    Dhar, N; Khan, N A; Chelvanathan, P; Akhtaruzzaman, M; Alam, M M; Alothman, Z A; Sopian, K; Amin, N

    2015-11-01

    Metal-semiconductor (MS) junction between Mo and CdTe, which is one of the fundamental issues for CdTe based solar cell, has been investigated for films deposited on different substrates. XRD pattern of Mo/CdTe films on the polyimide (PI) substrate shows a strong preferential orientation of MoTe2 in (100) at 2θ = 29.44 degrees, which becomes less apparent as deposition time of CdTe increases. However, on soda lime glass (SLG) no such XRD reflection pattern is observed. Moreover, from EDX measurement, Mo-Te compound also identifies MoTe2 at Mo/CdTe interface on PI substrate, which is not present on SLG. Bulk carrier concentration of Mo/CdTe films on PI substrate for lower deposition time of CdTe is found 1.42 x 10(18) cm(-3), which is almost equal to MoTe2. Thereafter, it decreases as CdTe growth time increases. The type of unintentionally formed MoTe2 on PI substrate is found to be n-type in nature. Lattice constants of a = 6.5 Å for CdTe and a = 3.52 Å for MoTe2 are found from nanostructure study by TEM.

  11. Cu{sub 2}S as ohmic back contact for CdTe solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Türck, Johannes; Siol, Sebastian; Mayer, Thomas; Klein, Andreas; Jaegermann, Wolfram, E-mail: jaegermann@surface.tu-darmstadt.de

    2015-05-01

    We prepared a back contact for CdTe solar cells with Cu{sub 2}S as primary contact. Cu{sub 2}S was evaporated on CdCl{sub 2} treated CdTe solar cells in superstrate configuration. The CdTe and CdS layers were deposited by Closed Space Sublimation. Direct interface studies with X-ray photoelectron spectroscopy have revealed a strongly reactive interface between CdTe and Cu{sub 2}S. A valence band offset of 0.4-0.6 eV has been determined. The performance of solar cells with Cu{sub 2}S back contacts was studied in comparison to cells with an Au contact that deposited onto a CdCl{sub 2}-treated CdTe surface that was chemically etched using a nitric-phosphoric etch. The solar cells were analyzed by current-voltage curves and external quantum efficiency measurements. After several post deposition annealing steps, 13% efficiency was reached with the Cu{sub 2}S back contact, which was significantly higher than the ones obtained for the NP-etched back contacts. - Highlights: • A new back contact for CdTe solar out of Cu{sub 2}S has been tested. • With a direct interface experiment the valence band offset was determined. • Post deposition heat treatment has been carried out for the solar cells. • 13% efficiency has been reached with the Cu{sub 2}S back contact.

  12. Structural and optical properties of alloyed quaternary CdSeTeS core and CdSeTeS/ZnS core–shell quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Adegoke, Oluwasesan, E-mail: adegoke.sesan@mailbox.co.za [Department of Chemistry, Faculty of Natural and Agricultural Sciences, University of Pretoria, Lynnwood Road, Pretoria 0002 (South Africa); Nyokong, Tebello, E-mail: t.nyokong@ru.ac.za [Department of Chemistry, Rhodes University, Grahamstown 6140 (South Africa); Forbes, Patricia B.C., E-mail: patricia.forbes@up.ac.za [Department of Chemistry, Faculty of Natural and Agricultural Sciences, University of Pretoria, Lynnwood Road, Pretoria 0002 (South Africa)

    2015-10-05

    Highlights: • Alloyed quaternary CdSeTeS core quantum dots (QDs) were synthesized. • Passivation was carried out using a ZnS shell. • Quaternary CdSeTeS core exhibited unique optical properties over CdSeTe/ZnS. • CdSeTeS can be employed as a useful alternative to core/shell QDs. - Abstract: Synthesis of fluorescent alloyed quantum dots (QDs) with unique optical properties suitable for a wide array of chemical, physical and biological applications is of research interest. In this work, highly luminescent and photostable alloyed quaternary CdSeTeS core QDs of two different sizes were fabricated via the organometallic hot-injection synthetic route. Characterization of the nanocrystals were performed using TEM, XRD, UV/vis and fluorescence spectrophotometric techniques. We have demonstrated in this work that the well fabricated alloyed quaternary CdSeTeS core QDs possess unique optical properties that are advantageous over conventional core/shell systems. Formation of the CdSeTeS/ZnS core/shell with the desired optical properties comes with a number of challenges, hence the advantages of the quaternary alloyed core over the core/shell QDs are (i) avoidance of the challenging process of determining the proper shell thickness which can provide the desired optical properties in the core/shell system and (ii) avoidance of the lattice-induced mismatch between the core and the shell material which can either lead to incomplete exciton confinement or dislocation at the core/shell interface.

  13. Charge separation and transfer in hybrid type II tunneling structures of CdTe and CdSe nanocrystals

    Energy Technology Data Exchange (ETDEWEB)

    Gross, Dieter Konrad Michael

    2013-11-08

    Closely packed nanocrystal systems have been investigated in this thesis with respect to charge separation by charge carrier tunneling. Clustered and layered samples have been analyzed using PL-measurements and SPV-methods. The most important findings are reviewed in the following. A short outlook is also provided for potential further aspects and application of the presented results. The main purpose of this thesis was to find and quantify electronic tunneling transfer in closely packed self-assembled nanocrystal structures presenting quantum mechanical barriers of about 1 nm width. We successfully used hybrid assemblies of CdTe and CdSe nanocrystals where the expected type II alignment between CdTe and CdSe typically leads to a concentration of electrons in CdSe and holes in CdTe nanocrystals. We were able to prove the charge selectivity of the CdTe-CdSe nanocrystal interface which induces charge separation. We mainly investigated the effects related to the electron transfer from CdTe to CdSe nanocrystals. Closely packing was achieved by two independent methods: the disordered colloidal clustering in solution and the layered assembly on dry glass substrates. Both methods lead to an inter-particle distance of about 1 nm of mainly organic material which acts as a tunneling barrier. PL-spectroscopy was applied. The PL-quenching of the CdTe nanocrystals in hybrid assemblies indicates charge separation by electron transfer from CdTe to CdSe nanocrystals. A maximum quenching rate of up to 1/100 ps was measured leading to a significant global PL-quenching of up to about 70 % for the CdTe nanocrystals. It was shown that charge separation dynamics compete with energy transfer dynamics and that charge separation typically dominates. The quantum confinement effect was used to tune the energetic offset between the CdTe and CdSe nanocrystals. We thus observe a correlation of PL-quenching and offset of the energy states for the electron transfer. The investigated PL

  14. Charge separation and transfer in hybrid type II tunneling structures of CdTe and CdSe nanocrystals

    Energy Technology Data Exchange (ETDEWEB)

    Gross, Dieter Konrad Michael

    2013-11-08

    Closely packed nanocrystal systems have been investigated in this thesis with respect to charge separation by charge carrier tunneling. Clustered and layered samples have been analyzed using PL-measurements and SPV-methods. The most important findings are reviewed in the following. A short outlook is also provided for potential further aspects and application of the presented results. The main purpose of this thesis was to find and quantify electronic tunneling transfer in closely packed self-assembled nanocrystal structures presenting quantum mechanical barriers of about 1 nm width. We successfully used hybrid assemblies of CdTe and CdSe nanocrystals where the expected type II alignment between CdTe and CdSe typically leads to a concentration of electrons in CdSe and holes in CdTe nanocrystals. We were able to prove the charge selectivity of the CdTe-CdSe nanocrystal interface which induces charge separation. We mainly investigated the effects related to the electron transfer from CdTe to CdSe nanocrystals. Closely packing was achieved by two independent methods: the disordered colloidal clustering in solution and the layered assembly on dry glass substrates. Both methods lead to an inter-particle distance of about 1 nm of mainly organic material which acts as a tunneling barrier. PL-spectroscopy was applied. The PL-quenching of the CdTe nanocrystals in hybrid assemblies indicates charge separation by electron transfer from CdTe to CdSe nanocrystals. A maximum quenching rate of up to 1/100 ps was measured leading to a significant global PL-quenching of up to about 70 % for the CdTe nanocrystals. It was shown that charge separation dynamics compete with energy transfer dynamics and that charge separation typically dominates. The quantum confinement effect was used to tune the energetic offset between the CdTe and CdSe nanocrystals. We thus observe a correlation of PL-quenching and offset of the energy states for the electron transfer. The investigated PL

  15. Changes in CdS/CdTe Solar Cells Subjected to Elevated Temperature, Voltage and Illumination

    Science.gov (United States)

    Demtsu, Samuel; Nagle, Tim

    2003-10-01

    CdTe/CdS solar cells have been known to exhibit degradation in performance after being subjected to elevated temperature, voltage and illumination. These conditions are collectively referred to as "stress". We have studied and presented CdTe/CdS cell degradation under different stress conditions of devices from First Solar Inc., the University of South Florida and the University of Toledo. All cells were stressed in the light (close to 100 mW/cm2) for 56 days at elevated temperature of 900C at two different biases, short circuit (SC) and open circuit (OC). The stress condition surpasses the operation conditions expected in the field. To characterize the cells, we have measured current density as function of the applied voltage (JV), capacitance vs bias voltage (CV) and quantum efficiency (QE) measurements before and after exposure to stress. To investigate the spatial non-uniformity of photocurrent collection induced by stress we have done Light Beam-Induced Current (LBIC) measurement. The effect of the stress on the photovoltaic parameters short-circuit current (Jsc), open-circuit voltage (Voc), Fill-Factor (FF), and efficiency is presented and discussed. Carrier density as a function of the distance from the semiconductor junction is extracted from the C-V measurements. We have seen some variations between cells and degradation was not monotonic with stress time. The highly probable explanation for the degradation of the cells after the stress is that mobile copper ions diffuse out of the back contact towards the primary junction leaving a depletion of Cu in the back contact, which increases the contact barrier.

  16. Conductive Atomic Free Microscopy of CdTe/CdS Solar Cells

    Energy Technology Data Exchange (ETDEWEB)

    Moutinho, H. R.; Dhere, R. G.; Jiang, C. S.; Al-Jassim, M. M.; Kazmerski, L. L.

    2005-01-01

    Conductive atomic force microscopy (C-AFM) is a recently developed technique that applies an electric voltage between a very sharp tip and the sample, permitting the study of the electrical properties of the sample with very high spatial resolution. It also provides current-voltage measurements at well-defined spots. C-AFM is applied simultaneously with atomic force microscopy, providing topographic and current images of the same region. In this work, we analyze CdTe/CdS samples, before and after CdCl2 treatment, and after bromine/methanol and nitric/phosphoric etches. The as-deposited samples show grains with different contrasts, indicating that the material is not electrically uniform. The CdCl2 treatment resulted in less conductive grain boundaries, suggesting a relative decrease in the conductivity at these locations. After the bromine/methanol etch, the conductivity at grains boundaries was higher than inside the grains, whereas for the nitric/phosphoric etch the conductivity increased over the entire surface.

  17. Electrical properties of CdTe/CdS solar cells investigated with conductive atomic force microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Moutinho, H.R. [National Renewable Energy Laboratory, 1617 Cole Blvd., Golden, CO 80401 (United States)]. E-mail: helio_moutinho@nrel.gov; Dhere, R.G. [National Renewable Energy Laboratory, 1617 Cole Blvd., Golden, CO 80401 (United States); Jiang, C.-S. [National Renewable Energy Laboratory, 1617 Cole Blvd., Golden, CO 80401 (United States); Al-Jassim, M.M. [National Renewable Energy Laboratory, 1617 Cole Blvd., Golden, CO 80401 (United States); Kazmerski, L.L. [National Renewable Energy Laboratory, 1617 Cole Blvd., Golden, CO 80401 (United States)

    2006-08-30

    We report on the application of conductive atomic force microscopy (C-AFM) for studying the electrical properties of CdTe/CdS solar cells, and discuss the advantages and limitations of this technique. C-AFM is a new technique that uses the tip of an AFM to apply a potential between the tip and the sample, resulting in high spatial-resolution current images, as well as current versus voltage curves. The analyses were made before and after the standard vapor CdCl{sub 2} treatment, as well as two etching processes, using solutions of bromine/methanol and nitric-phosphoric acids. The current images from the untreated and CdCl{sub 2}-treated samples showed grains with different contrasts, due to differences in electrical conductivity or a nonuniform surface. The bromine/methanol etch resulted in more conductive grain boundaries as compared to intragrain material, while the nitric/phosphoric etch increased the conductivity of the whole film close to the surface and resulted in films with significant photocurrent.

  18. Size distribution effects of cadmium tellurium quantum dots (CdS/CdTe) immunotoxicity on aquatic organisms.

    Science.gov (United States)

    Bruneau, A; Fortier, M; Gagne, F; Gagnon, C; Turcotte, P; Tayabali, A; Davis, T L; Auffret, M; Fournier, M

    2013-03-01

    The increasing use of products derived from nanotechnology has raised concern about their potential toxicity to aquatic life. This study sought to examine the comparative immunotoxicity of capped cadmium sulphide/cadmium telluride (CdS/CdTe) quantum dots (QDs) and possible impact of particle/aggregate size on two bivalves (Mytilus edulis and Elliptio complanata) and a fish (Oncorhynchus mykiss). The QDs were dispersed in sterile water and fractionated using a series of micro/ultrafiltration membranes of decreasing pore size: 450 nm, 100 nm, 50 nm, 25 nm, 100 kDa (6.8 nm), 30 kDa (4.6 nm), 10 kDa (3.2 nm) and 1 kDa (1.5 nm). The total concentrations of cadmium and tellurium were determined for the filtered material and for that retained on the filters (retentate). The immunotoxicity was determined by measuring cell viability and phagocytosis. Results revealed that nanoparticles retained on the ultrafilters had a higher Cd/Te ratio compared to the permeate fraction (ratio of 5 and 2 respectively) which could indicate that the CdS core was not associated with the permeable fraction of Cd. Our results demonstrate that the toxicity of CdS/CdTe QDs was concentration and size dependent. Large CdS/CdTe QD aggregates (25 nm < size < 100 nm) reduced phagocytosis more than did smaller nanoparticles (<25 nm). Moreover, our results revealed that the different species responded differently to these fractions. Mytilus edulis hemocytes were less sensitive to CdS/CdTe QDs than the Oncorhynchus mykiss macrophage and Elliptio complanata hemocytes.

  19. CdTe solar cell degradation studies with the use of CdS as the window material

    Energy Technology Data Exchange (ETDEWEB)

    Mendoza-Perez, R. [Universidad Autonoma de la Ciudad de Mexico, Av. Prolongacion San Isidro Num. 151, Col. San Lorenzo Tezonco, C.P. 09790 Mexico, D.F. (Mexico); Escuela Superior de Fisica y Matematicas del IPN., Edificio 9, U.P.A.L.M., Col. Lindavista, C.P. 07738 Mexico, D.F. (Mexico); Sastre-Hernandez, J.; Contreras-Puente, G.; Vigil-Galan, O. [Escuela Superior de Fisica y Matematicas del IPN., Edificio 9, U.P.A.L.M., Col. Lindavista, C.P. 07738 Mexico, D.F. (Mexico)

    2009-01-15

    We present in this work the degradation effects with time in thin film CdTe/CdS solar cells, where the CdS and CdTe layers are deposited by chemical bath deposition (CBD) and close space vapor transport (CSVT), respectively. The CdS thin films were grown from different baths by varying the S/Cd ratio. The variation of the S/Cd ratio allowed us to control the morphology and the density of defects, thus giving rise to better quality CBD CdS films. Depending on the S/Cd ratio an improvement of the morphology and capacitance signal was observed, these factors have also an influence on the open-circuit voltage, short-circuit current density, fill factor and conversion efficiency of the solar cell. The variation with time of these parameters in our devices was tracked during a period of 3 years measured directly on the exposed back contact regions (CdTe/Cu/Au). A discussion on the deterioration of the photovoltaic (PV) performance of the solar cells is presented in correlation with the local environmental conditions. This particular environment has contamination, and represents another type of stress for standard PV operations. These conditions reduce the mean life time of solar cells beyond short periods; this can be of interest for PV community. (author)

  20. Controllable photoluminescence enhancement of CdTe/CdS quantum dots thin films incorporation with Au nanoparticles.

    Science.gov (United States)

    Wang, Hongyu; Xu, Ling; Zhang, Renqi; Ge, Zhaoyun; Zhang, Wenping; Xu, Jun; Ma, Zhongyuan; Chen, Kunji

    2015-01-01

    Au nanoparticles (Au NPs)/CdTe/CdS QDs nanocomposite films were fabricated by deposition of Au NPs and layer-by-layer self-assembly of colloidal CdTe/CdS QDs. Photoluminescence (PL) spectra showed that Au NPs incorporation resulted in an increase of PL intensity about 16-fold compared with that of the samples without Au NPs. PL enhancement of Au NPs/CdTe/CdS QDs nanocomposite films can be controlled by tuning the thickness of spacer layer between the metal nanoparticles (MNPs) and QDs. Optical absorption spectra exhibited the incorporation of Au NPs boosted the absorption of Au NPs/CdTe/CdS QDs nanocomposite films. The results of finite-difference time-domain (FDTD) simulation indicated that the increased sizes of Au NPs resulted in stronger localization of electric field, which boosted the PL intensity of QDs in the vicinity of Au NPs. We thought that these were mainly attributed to localized SP enhancement effects of the Au NPs. Our experiment results demonstrated that Au NPs/QDs nanocomposite films would be a promising candidate for optoelectronic devices application. PACS 78.55.-m; 82.33.Ln; 68.65.Hb.