WorldWideScience

Sample records for narrow bandgap solar

  1. The importance of surface recombination and energy-bandgap narrowing in p-n-junction silicon solar cells

    Science.gov (United States)

    Fossum, J. G.; Lindholm, F. A.; Shibib, M. A.

    1979-01-01

    Experimental data demonstrating the sensitivity of open-circuit voltage to front-surface conditions are presented for a variety of p-n-junction silicon solar cells. Analytical models accounting for the data are defined and supported by additional experiments. The models and the data imply that a) surface recombination significantly limits the open-circuit voltage (and the short-circuit current) of typical silicon cells, and b) energy-bandgap narrowing is important in the manifestation of these limitations. The models suggest modifications in both the structural design and the fabrication processing of the cells that would result in substantial improvements in cell performance. The benefits of one such modification - the addition of a thin thermal silicon-dioxide layer on the front surface - are indicated experimentally.

  2. Bandgap narrowing in moderately to heavily doped silicon

    Science.gov (United States)

    Lanyon, H. P. D.; Tuft, R. A.

    1979-01-01

    A theoretical model of bandgap narrowing in silicon at high doping levels has been developed. The model takes into account the electrostatic energy of interaction between a minority carrier and the majority carriers surrounding it, which reduces the thermal energy necessary for creation of an electron-hole pair. A pair energy similar to the excitonic binding energy of bound electron-hole pairs in insulators is obtained. Theoretical results are in excellent agreement with experimental results in the doping range from 3 times 10 to the 17th to 1.5 times 10 to the 20th/cu cm at room temperature. These results indicate that at high injection levels such as a transistor biased into the conductivity-modulation regime or a solar cell whose surface is established by ion implantation into an oxide layer, the bandgap narrowing is determined by the injected carrier concentration rather than by the doping level.

  3. Elucidating double aggregation mechanisms in the morphology optimization of diketopyrrolopyrrole-based narrow bandgap polymer solar cells.

    Science.gov (United States)

    Gao, Jing; Chen, Wei; Dou, Letian; Chen, Chun-Chao; Chang, Wei-Hsuan; Liu, Yongsheng; Li, Gang; Yang, Yang

    2014-05-21

    The power conversion efficiency (PCE) of a DPP-based polymer solar cell is significantly improved by using DIO or DCB as processing additives. The discovery that DCB outperforms DIO with a significantly wider solvent mixture operation window suggests different optimization mechanisms. Although both solvent mixture systems involve double aggregation processes, including a similar solution-to-film aggregation, however, two distinct solution-stage aggregations are observed: relatively amorphous polymer aggregates form in the CF-DIO solution, while more crystalline polymer aggregates form in CF-DCB solution.

  4. New Coefficients of the Minority Carrier Lifetime and Bandgap Narrowing Models in the Transparent Emitter of Thin Film Silicon Solar Cells

    OpenAIRE

    2001-01-01

    In this study we have determined new coefficients for the physical model describing the band-gap narrowing and the minority carriers lifetime. This was accomplished according to the doping level of the thin emitter. This model allows us to take into account both the effects of the heavy doping and the majority carrier degeneration for the very high level of doping. The results we obtain by the corrected model are in good agreement with those reported in the literature and in di...

  5. Graded bandgap perovskite solar cells

    Science.gov (United States)

    Ergen, Onur; Gilbert, S. Matt; Pham, Thang; Turner, Sally J.; Tan, Mark Tian Zhi; Worsley, Marcus A.; Zettl, Alex

    2017-05-01

    Organic-inorganic halide perovskite materials have emerged as attractive alternatives to conventional solar cell building blocks. Their high light absorption coefficients and long diffusion lengths suggest high power conversion efficiencies, and indeed perovskite-based single bandgap and tandem solar cell designs have yielded impressive performances. One approach to further enhance solar spectrum utilization is the graded bandgap, but this has not been previously achieved for perovskites. In this study, we demonstrate graded bandgap perovskite solar cells with steady-state conversion efficiencies averaging 18.4%, with a best of 21.7%, all without reflective coatings. An analysis of the experimental data yields high fill factors of ~75% and high short-circuit current densities up to 42.1 mA cm-2. The cells are based on an architecture of two perovskite layers (CH3NH3SnI3 and CH3NH3PbI3-xBrx), incorporating GaN, monolayer hexagonal boron nitride, and graphene aerogel.

  6. New Coefficients of the Minority Carrier Lifetime and Bandgap Narrowing Models in the Transparent Emitter of Thin Film Silicon Solar Cells

    OpenAIRE

    2003-01-01

    In this study we have determined new coefficients for the physical model describing the band-gap narrowing and the minority carriers lifetime. This was accomplished according to the doping level of the thin emitter. This model allows us to take into account both the effects of the heavy doping and the majority carrier degeneration for the very high level of doping. The results we obtain by the corrected model are in good agreement with those reported in the literature and in different expe...

  7. High-Performance Photothermal Conversion of Narrow-Bandgap Ti2 O3 Nanoparticles.

    Science.gov (United States)

    Wang, Juan; Li, Yangyang; Deng, Lin; Wei, Nini; Weng, Yakui; Dong, Shuai; Qi, Dianpeng; Qiu, Jun; Chen, Xiaodong; Wu, Tom

    2017-01-01

    Ti2 O3 nanoparticles with high performance of photothermal conversion are demonstrated for the first time. Benefiting from the nanosize and narrow-bandgap features, the Ti2 O3 nanoparticles possess strong light absorption and nearly 100% internal solar-thermal conversion efficiency. Furthermore, Ti2 O3 -nanoparticle-based thin film shows potential use in seawater desalination and purification.

  8. Novel Narrow Bandgap Photovoltaic Materials in Polymer Solar Cells%新型窄带隙聚合物太阳能电池光伏材料

    Institute of Scientific and Technical Information of China (English)

    辛铁军; 张秋禹; 陈少杰; 李伟; 刘梦娇; 周伦伟

    2012-01-01

    聚合物太阳能电池中给体材料的能级水平、带隙、光吸收系数、溶解性、成膜性及载流子迁移率是决定器件性能的关键因素.阐述了聚合物太阳能电池中给体材料的最新研究进展,着重介绍了含有苯并双噻吩的窄带隙D-A类型的共聚物,并对一些给体材料的能级水平优化结果做了简单的总结.最后指出了未来聚合物太阳能电池给体材料今后的发展方向.%The performance of devices is depend on the energy levels,bandgap, light absorption coeffcient, solubility, film forming ability and carrier mobility of the donor materials in polymer solar cells. The recent progress of the donor materials in polymer solar cells is reviewed, and the containing benzo bisthien of D-A copolymers is introduced. The energy levels optimization results of the donor materials are summarized. Furthermore, the future prospects of the domor materials in polymer solar cells are pointed out.

  9. Photonic bandgap narrowing in conical hollow core Bragg fibers

    Energy Technology Data Exchange (ETDEWEB)

    Ozturk, Fahri Emre; Yildirim, Adem; Kanik, Mehmet [UNAM-National Nanotechnology Research Center, Bilkent University, 06800 Ankara (Turkey); Institute of Materials Science and Nanotechnology, Bilkent University, 06800 Ankara (Turkey); Bayindir, Mehmet, E-mail: bayindir@nano.org.tr [UNAM-National Nanotechnology Research Center, Bilkent University, 06800 Ankara (Turkey); Institute of Materials Science and Nanotechnology, Bilkent University, 06800 Ankara (Turkey); Department of Physics, Bilkent University, 06800 Ankara (Turkey)

    2014-08-18

    We report the photonic bandgap engineering of Bragg fibers by controlling the thickness profile of the fiber during the thermal drawing. Conical hollow core Bragg fibers were produced by thermal drawing under a rapidly alternating load, which was applied by introducing steep changes to the fiber drawing speed. In conventional cylindrical Bragg fibers, light is guided by omnidirectional reflections from interior dielectric mirrors with a single quarter wave stack period. In conical fibers, the diameter reduction introduced a gradient of the quarter wave stack period along the length of the fiber. Therefore, the light guided within the fiber encountered slightly smaller dielectric layer thicknesses at each reflection, resulting in a progressive blueshift of the reflectance spectrum. As the reflectance spectrum shifts, longer wavelengths of the initial bandgap cease to be omnidirectionally reflected and exit through the cladding, which narrows the photonic bandgap. A narrow transmission bandwidth is particularly desirable in hollow waveguide mid-infrared sensing schemes, where broadband light is coupled to the fiber and the analyte vapor is introduced into the hollow core to measure infrared absorption. We carried out sensing simulations using the absorption spectrum of isopropyl alcohol vapor to demonstrate the importance of narrow bandgap fibers in chemical sensing applications.

  10. High-Efficiency Solar Cells Using Photonic-Bandgap Materials

    Science.gov (United States)

    Dowling, Jonathan; Lee, Hwang

    2005-01-01

    Solar photovoltaic cells would be designed to exploit photonic-bandgap (PBG) materials to enhance their energy-conversion efficiencies, according to a proposal. Whereas the energy-conversion efficiencies of currently available solar cells are typically less than 30 percent, it has been estimated that the energy-conversion efficiencies of the proposed cells could be about 50 percent or possibly even greater. The primary source of inefficiency of a currently available solar cell is the mismatch between the narrow wavelength band associated with the semiconductor energy gap (the bandgap) and the broad wavelength band of solar radiation. This mismatch results in loss of power from both (1) long-wavelength photons, defined here as photons that do not have enough energy to excite electron-hole pairs across the bandgap, and (2) short-wavelength photons, defined here as photons that excite electron- hole pairs with energies much above the bandgap. It follows that a large increase in efficiency could be obtained if a large portion of the incident solar energy could be funneled into a narrow wavelength band corresponding to the bandgap. In the proposed approach, such funneling would be effected by use of PBG materials as intermediaries between the Sun and photovoltaic cells.

  11. Defect-induced bandgap narrowing in low-k dielectrics

    Energy Technology Data Exchange (ETDEWEB)

    Guo, X.; Zheng, H.; Shohet, J. L. [Plasma Processing & Technology Laboratory and Department of Electrical and Computer Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States); King, S. W. [Logic Technology Development, Intel Corporation, Hillsboro, Oregon 97124 (United States); Afanas' ev, V. V. [Department of Physics, University of Leuven, B-3001 Leuven (Belgium); Baklanov, M. R.; Marneffe, J.-F. de [IMEC, Kapeldreef 75, B-3001 Leuven (Belgium); Nishi, Y. [Department of Electrical Engineering, Stanford University, Stanford, California 94305 (United States)

    2015-08-24

    In this work, core-level X-ray photoelectron spectroscopy was utilized to determine the surface bandgap for various porous and non-porous low-k a-SiCOH dielectrics before and after ion sputtering. By examining the onset of inelastic energy loss in O 1s core-level spectra, the gap narrowing was universally found in Ar{sup +} ion sputtered low-k dielectrics. The reduction of the bandgap ranges from 1.3 to 2.2 eV depending on the film composition. We show that the bandgap narrowing in these low-k dielectrics is caused by development of the valence-band tail as evidenced by the presence of additional electronic states above the valence-band maximum. Electron-spin-resonance measurements were made on a-SiCOH films to gain atomic insight into the nature of the sputtering-induced defects and reveal formation of carbon-related defects as the most probable origin of the gap states.

  12. Simultaneous band-gap narrowing and carrier-lifetime prolongation of organic–inorganic trihalide perovskites

    Energy Technology Data Exchange (ETDEWEB)

    Kong, Lingping; Liu, Gang; Gong, Jue; Hu, Qingyang; Schaller, Richard D.; Dera, Przemyslaw; Zhang, Dongzhou; Liu, Zhenxian; Yang, Wenge; Zhu, Kai; Tang, Yuzhao; Wang, Chuanyi; Wei, Su-Huai; Xu, Tao; Mao, Ho-kwang

    2016-07-21

    The organic-inorganic hybrid lead trihalide perovskites have been emerging as the most attractive photovoltaic materials. As regulated by Shockley-Queisser theory, a formidable materials science challenge for improvement to the next level requires further band-gap narrowing for broader absorption in solar spectrum, while retaining or even synergistically prolonging the carrier lifetime, a critical factor responsible for attaining the near-band-gap photovoltage. Herein, by applying controllable hydrostatic pressure, we have achieved unprecedented simultaneous enhancement in both band-gap narrowing and carrier-lifetime prolongation (up to 70% to -100% increase) under mild pressures at -0.3 GPa. The pressure-induced modulation on pure hybrid perovskites without introducing any adverse chemical or thermal effect clearly demonstrates the importance of band edges on the photon-electron interaction and maps a pioneering route toward a further increase in their photovoltaic performance.

  13. Simultaneous band-gap narrowing and carrier-lifetime prolongation of organic-inorganic trihalide perovskites.

    Science.gov (United States)

    Kong, Lingping; Liu, Gang; Gong, Jue; Hu, Qingyang; Schaller, Richard D; Dera, Przemyslaw; Zhang, Dongzhou; Liu, Zhenxian; Yang, Wenge; Zhu, Kai; Tang, Yuzhao; Wang, Chuanyi; Wei, Su-Huai; Xu, Tao; Mao, Ho-Kwang

    2016-08-09

    The organic-inorganic hybrid lead trihalide perovskites have been emerging as the most attractive photovoltaic materials. As regulated by Shockley-Queisser theory, a formidable materials science challenge for improvement to the next level requires further band-gap narrowing for broader absorption in solar spectrum, while retaining or even synergistically prolonging the carrier lifetime, a critical factor responsible for attaining the near-band-gap photovoltage. Herein, by applying controllable hydrostatic pressure, we have achieved unprecedented simultaneous enhancement in both band-gap narrowing and carrier-lifetime prolongation (up to 70% to ∼100% increase) under mild pressures at ∼0.3 GPa. The pressure-induced modulation on pure hybrid perovskites without introducing any adverse chemical or thermal effect clearly demonstrates the importance of band edges on the photon-electron interaction and maps a pioneering route toward a further increase in their photovoltaic performance.

  14. Simultaneous band-gap narrowing and carrier-lifetime prolongation of organic–inorganic trihalide perovskites

    Science.gov (United States)

    Kong, Lingping; Liu, Gang; Gong, Jue; Hu, Qingyang; Schaller, Richard D.; Dera, Przemyslaw; Zhang, Dongzhou; Liu, Zhenxian; Yang, Wenge; Zhu, Kai; Tang, Yuzhao; Wang, Chuanyi; Wei, Su-Huai; Xu, Tao; Mao, Ho-kwang

    2016-01-01

    The organic–inorganic hybrid lead trihalide perovskites have been emerging as the most attractive photovoltaic materials. As regulated by Shockley–Queisser theory, a formidable materials science challenge for improvement to the next level requires further band-gap narrowing for broader absorption in solar spectrum, while retaining or even synergistically prolonging the carrier lifetime, a critical factor responsible for attaining the near-band-gap photovoltage. Herein, by applying controllable hydrostatic pressure, we have achieved unprecedented simultaneous enhancement in both band-gap narrowing and carrier-lifetime prolongation (up to 70% to ∼100% increase) under mild pressures at ∼0.3 GPa. The pressure-induced modulation on pure hybrid perovskites without introducing any adverse chemical or thermal effect clearly demonstrates the importance of band edges on the photon–electron interaction and maps a pioneering route toward a further increase in their photovoltaic performance. PMID:27444014

  15. New Coefficients of the Minority Carrier Lifetime and Bandgap Narrowing Models in the Transparent Emitter of Thin Film Silicon Solar Cells

    Directory of Open Access Journals (Sweden)

    A. Zerga

    2003-01-01

    literature and in different experiments. They show us the possibility of accurately evaluating the performances for the n+p silicon solar cell. This model is then used to introduce a new concept for the thin layer emitter, called transparent emitter.

  16. Intermediate Bandgap Solar Cells From Nanostructured Silicon

    Energy Technology Data Exchange (ETDEWEB)

    Black, Marcie [Bandgap Engineering, Lincoln, MA (United States)

    2014-10-30

    This project aimed to demonstrate increased electronic coupling in silicon nanostructures relative to bulk silicon for the purpose of making high efficiency intermediate bandgap solar cells using silicon. To this end, we formed nanowires with controlled crystallographic orientation, small diameter, <111> sidewall faceting, and passivated surfaces to modify the electronic band structure in silicon by breaking down the symmetry of the crystal lattice. We grew and tested these silicon nanowires with <110>-growth axes, which is an orientation that should produce the coupling enhancement.

  17. Band-gap narrowing in heavily doped silicon: A comparison of optical and electrical data

    Science.gov (United States)

    Wagner, Joachim; del Alamo, Jesús A.

    1988-01-01

    The band-gap narrowing in heavily doped silicon has been studied by optical techniques—namely, photoluminescence and photoluminescence excitation spectroscopy—and by electrical measurements on bipolar transistors. The optical experiments give a consistent set of data for the band-gap narrowing in n- and p-type material at low temperatures as well as at room temperature. A good agreement is found between the optical and electrical data removing the discrepancies existing so far in the literature.

  18. Surface band-gap narrowing in quantized electron accumulation layers.

    Science.gov (United States)

    King, P D C; Veal, T D; McConville, C F; Zúñiga-Pérez, J; Muñoz-Sanjosé, V; Hopkinson, M; Rienks, E D L; Jensen, M Fuglsang; Hofmann, Ph

    2010-06-25

    An energy gap between the valence and the conduction band is the defining property of a semiconductor, and the gap size plays a crucial role in the design of semiconductor devices. We show that the presence of a two-dimensional electron gas near to the surface of a semiconductor can significantly alter the size of its band gap through many-body effects caused by its high electron density, resulting in a surface band gap that is much smaller than that in the bulk. Apart from reconciling a number of disparate previous experimental findings, the results suggest an entirely new route to spatially inhomogeneous band-gap engineering.

  19. Image-potential band-gap narrowing at a metal/semiconductor interface

    OpenAIRE

    2001-01-01

    GW approximation is used to systematically revisit the image-potential band-gap narrowing at metal/semiconductor interfaces proposed by Inkson in the 1970's. Here we have questioned how the narrowing as calculated from quasi-particle energy spectra for the jellium/Si interface depends on $r_s$ of the jellium. The gap narrowing is found to only weakly depend on $r_s$ (i.e., narrowing $\\simeq 0.3$ eV even for a large $r_s = 6)$. Hence we can turn to smaller polarizability in the semiconductor s...

  20. Application Progress of the Narrow Band-gap Conjugated Polymer Base on Carbazolyl Materials for Solar Cells%咔唑基窄带隙共轭聚合物太阳能电池材料的研究进展

    Institute of Scientific and Technical Information of China (English)

    苏雪花; 夏德强; 王守伟

    2012-01-01

    基于咔唑基窄带隙共轭聚合物的太阳能电池材料的研究取得突破性的进展,成为当前聚合物光伏器件研究的热点课题之一。概述了咔唑基窄带隙共轭聚合物作为电子给体材料的研究进展及存在的问题,提出了光谱响应更宽、光电转换效率更高的咔唑基共轭聚合物研究的发展前景。%The study of the narrow band-gap conjugated polymer base on carbazolyl materials for application in solar cells gained breakthrough progress,and became one of hotspot issue of the polymer photovoltaic device research at present.The research progress and its main existing problems of the narrow band-gap conjugated polymers base on carbazolyl as electron donor materials were summarized,the study development prospects of the conjugated polymers based on carbazole with broader spectral response and higher incident photon-to-current conversion efficiency were proposed.

  1. First principle analyses of direct bandgap solar cells with absorbing substrates versus mirrors

    Science.gov (United States)

    Kirk, Alexander P.; Kirk, Wiley P.

    2013-11-01

    Direct bandgap InP, GaAs, CdTe, and Ga0.5In0.5P solar cells containing backside mirrors as well as parasitically absorbing substrates are analyzed for their limiting open circuit voltage and power conversion efficiency with comparison to record solar cells. From the principle of detailed balance, it is shown quantitatively that mirror solar cells have greater voltage and power conversion efficiency than their substrate counterparts. Next, the radiative recombination coefficient and maximum radiative lifetime of GaAs mirror and substrate solar cells are calculated and compared to the nonradiative Auger and Shockley-Read-Hall (SRH) lifetimes. Mirror solar cells have greater radiative lifetime than their substrate variants. Auger lifetime exceeds radiative lifetime for both substrate and mirror cells while SRH lifetime may be less or greater than radiative lifetime depending on trap concentration and capture cross section. Finally, the change in free energy of the photogenerated carriers is analyzed in a comparison between InP, GaAs, CdTe, and Ga0.5In0.5P mirror and substrate solar cells in order to characterize the relationship between solar photon quality and free energy management in solar cells with differing bandgaps. Wider bandgap visible threshold Ga0.5In0.5P solar cells make better use of the available change in free energy of the photogenerated charge carriers, even when normalized to the bandgap energy, than narrower bandgap near-IR threshold InP, GaAs, and CdTe solar cells.

  2. Solution-processable donor-acceptor polymers with modular electronic properties and very narrow bandgaps.

    Science.gov (United States)

    Foster, Michael E; Zhang, Benjamin A; Murtagh, Dustin; Liu, Yi; Sfeir, Matthew Y; Wong, Bryan M; Azoulay, Jason D

    2014-09-01

    Bridgehead imine-substituted cyclopentadithiophene structural units, in combination with highly electronegative acceptors that exhibit progressively delocalized π-systems, afford donor-acceptor (DA) conjugated polymers with broad absorption profiles that span technologically relevant wavelength (λ) ranges from 0.7 electronic properties so as to achieve very narrow optical bandgaps (Eg (opt) < 0.5 eV). This strategy affords modular DA copolymers with broad- and long-wavelength light absorption in the infrared and materials with some of the narrowest bandgaps reported to date.

  3. 含噻吩窄带隙共轭聚合物类太阳能电池材料的研究进展%Research Progress of Thiophene-based Narrow Bandgap Conjugated Polymers for Organic Solar Cell Applications

    Institute of Scientific and Technical Information of China (English)

    卢科蓉; 侯学清; 魏博; 高非

    2012-01-01

    含噻吩的窄带隙共轭聚合物类太阳能电池材料因其良好的稳定性和可加工性,已成为新型太阳能电池的研究热点。本论文主要介绍了用于太阳能电池的窄带隙共轭聚合物研究进展,按其结构特征分为烷基/烷氧基取代聚噻吩、含苯基聚噻吩、基于噻吩并吡嗪的共聚物、基于噻吩并噻唑的共聚物、基于噻吩并吩噻嗪的共聚物、基于烷基芴的共聚物以及其它种类的窄带隙的共轭聚合物,并对它们的结构特点、光学带隙、合成方法进行了归纳与总结。本文最后简要介绍了该研究领域目前所面临的一些问题,同时讨论了该类材料在此领域今后的发展趋势。%Thiophene-based narrow band gap conjugated polymers with good stability and machinability for Solar cell applications have been the hot topic of new solar cells. This paper mainly introduced research progress of narrow band gap conjugated polymers for solar cells. According to the structure characteristics, the narrow band gap conjugated polymer was divided into alkyl- or alkoxy- substituted polythiophene, polyisothianaphthene, thiophene-based copolymers, pyrazine, thiazole, phenothiazine, fluorene and others. And their structural characteristics, optical band gap, synthesis methods were summarized. In addition, the existing problems and the further trend of this kind of materials in this field have also been discussed in this paper.

  4. Magnetism switching and band-gap narrowing in Ni-doped PbTiO{sub 3} thin films

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, Wenliang; Yu, Lu; Yang, Pingxiong, E-mail: pxyang@ee.ecnu.edu.cn; Chu, Junhao [Key Laboratory of Polar Materials and Devices, Ministry of Education, Department of Electronic Engineering, East China Normal University, Shanghai 200241 (China); Deng, Hongmei [Instrumental Analysis and Research Center, Institute of Materials, Shanghai University, 99 Shangda Road, Shanghai 200444 (China)

    2015-05-21

    Ions doping-driven structural phase transition accompanied by magnetism switching and band-gap narrowing effects has been observed in PbTi{sub 1−x}Ni{sub x}O{sub 3−δ} (xPTNO, x = 0.00, 0.06, and 0.33) thin films. With the increase of x, the xPTNO thin films exhibit not only a phase transition from the pseudotetragonal structure to a centrosymmetric cubic structure but also a drastic decrease of grain size. Moreover, the as-grown Ni-doped PbTiO{sub 3} (PTO) thin films show obvious room-temperature ferromagnetism and an increased saturation magnetization with increasing the Ni content, in contrast to undoped PTO, which shows diamagnetism. A bound magnetic polaron model was proposed to understand the observed ferromagnetic behavior of PTO-derived perovskite thin films. Furthermore, the 0.33PTNO thin film presents a narrowed band-gap, much smaller than that of PTO, which is attributed to new states of both the highest occupied molecular orbital and the lowest unoccupied molecular orbital in an electronic structure with the presence of Ni. These findings may open up a route to explore promising perovskite oxides as candidate materials for use in multiferroics and solar-energy devices.

  5. Narrow Bandgap in beta-BaZn2As2 and Its Chemical Origins

    CERN Document Server

    Xiao, Zewen; Ueda, Shigenori; Toda, Yoshitake; Ran, Fan-Yong; Guo, Jiangang; Lei, Hechang; Matsuishi, Satoru; Hosono, Hideo; Kamiya, Toshio

    2015-01-01

    Beta-BaZn2As2 is known to be a p-type semiconductor with the layered crystal structure similar to that of LaZnAsO, leading to the expectation that beta-BaZn2As2 and LaZnAsO have similar bandgaps; however, the bandgap of beta-BaZn2As2 (previously-reported value ~0.2 eV) is one order of magnitude smaller than that of LaZnAsO (1.5 eV). In this paper, the reliable bandgap value of beta-BaZn2As2 is determined to be 0.23 eV from the intrinsic region of the tem-perature dependence of electrical conductivity. The origins of this narrow bandgap are discussed based on the chemi-cal bonding nature probed by 6 keV hard X-ray photoemission spectroscopy, hybrid density functional calculations, and the ligand theory. One origin is the direct As-As hybridization between adjacent [ZnAs] layers, which leads to a secondary splitting of As 4p levels and raises the valence band maximum. The other is that the non-bonding Ba 5dx2-y2 orbitals form unexpectedly deep conduction band minimum (CBM) in beta-BaZn2As2 although the CBM of L...

  6. Large Bandgap Semiconductors for Solar Water Splitting

    DEFF Research Database (Denmark)

    Malizia, Mauro

    water splitting devices having tandem design. The increase of the photovoltage produced by GaP under illumination was the main goal of this work. GaP has a bandgap of 2.25 eV and could in theory produce a photovoltage of approximately 1.7 V. Instead, the photovoltage produced by the semiconductor...... density generated by GaP was increased by more than 60% by electrochemical etching of the surface. The etching process produces a rough microstructured surface that increases the optical path length of the incident photons and the collection of photogenerated electrons.Furthermore, the synthesis of BiVO4...

  7. Sub-bandgap absorption in polymer-fullerene solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Presselt, Martin; Herrmann, Felix; Seeland, Marco; Baerenklau, Maik; Roesch, Roland; Shokhovets, Sviatoslav; Hopp, Harald; Gobsch, Gerhard [Experimental Physics I, Institute of Physics and Institute of Micro- und Nanotechnologies, Ilmenau University of Technology, Ilmenau (Germany); Beenken, Wichard J.D.; Runge, Erich [Theoretical Physics I, Institute of Physics, Ilmenau University of Technology, Ilmenau (Germany)

    2011-07-01

    We present external quantum efficiency (EQE) studies of P3HT:PCBM based bulk heterojunction polymer solar cells with improved intensity resolution in the sub-bandgap (SBG) region, i.e. the energy range below the optical bandgaps of the pristine materials. Varying the P3HT:PCBM blending ratio, we find that in addition to a Gaussian profile an exponential tail is needed for a quantitative description of the SBG EQE spectra. To gain insights into the origin of the single contributions, absorption and emission spectra covering several decades of intensity and SBG EQE signals are discussed in detail.

  8. Band-gap narrowing in the space-charge region of heavily doped silicon diodes

    Science.gov (United States)

    Lowney, Jeremiah R.

    1985-02-01

    The densities of states of the valence and conduction bands have been calculated in the space-charge region of a heavily doped linearly graded p- n junction silicon diode. Both the donor and acceptor densities were chosen to be equal to 6.2 × 10 18 cm -3. The results showed the emergence of band tails which penetrated deeply into the energy gap and accounted for the band-gap narrowing observed in such a diode by analysis of capacitance vs voltage measurements of the built-in voltage.

  9. Stabilized Wide Bandgap Perovskite Solar Cells by Tin Substitution.

    Science.gov (United States)

    Yang, Zhibin; Rajagopal, Adharsh; Jo, Sae Byeok; Chueh, Chu-Chen; Williams, Spencer; Huang, Chun-Chih; Katahara, John K; Hillhouse, Hugh W; Jen, Alex K-Y

    2016-12-14

    Wide bandgap MAPb(I1-yBry)3 perovskites show promising potential for application in tandem solar cells. However, unstable photovoltaic performance caused by phase segregation has been observed under illumination when y is above 0.2. Herein, we successfully demonstrate stabilization of the I/Br phase by partially replacing Pb(2+) with Sn(2+) and verify this stabilization with X-ray diffractometry and transient absorption spectroscopy. The resulting MAPb0.75Sn0.25(I1-yBry)3 perovskite solar cells show stable photovoltaic performance under continuous illumination. Among these cells, the one based on MAPb0.75Sn0.25(I0.4Br0.6)3 perovskite shows the highest efficiency of 12.59% with a bandgap of 1.73 eV, which make it a promising wide bandgap candidate for application in tandem solar cells. The engineering of internal bonding environment by partial Sn substitution is believed to be the main reason for making MAPb0.75Sn0.25(I1-yBry)3 perovskite less vulnerable to phase segregation during the photostriction under illumination. Therefore, this study establishes composition engineering of the metal site as a promising strategy to impart phase stability in hybrid perovskites under illumination.

  10. Matching Charge Extraction Contact for Wide-Bandgap Perovskite Solar Cells.

    Science.gov (United States)

    Lin, Yuze; Chen, Bo; Zhao, Fuwen; Zheng, Xiaopeng; Deng, Yehao; Shao, Yuchuan; Fang, Yanjun; Bai, Yang; Wang, Chunru; Huang, Jinsong

    2017-07-01

    Efficient wide-bandgap (WBG) perovskite solar cells are needed to boost the efficiency of silicon solar cells to beyond Schottky-Queisser limit, but they suffer from a larger open circuit voltage (VOC ) deficit than narrower bandgap ones. Here, it is shown that one major limitation of VOC in WBG perovskite solar cells comes from the nonmatched energy levels of charge transport layers. Indene-C60 bisadduct (ICBA) with higher-lying lowest-unoccupied-molecular-orbital is needed for WBG perovskite solar cells, while its energy-disorder needs to be minimized before a larger VOC can be observed. A simple method is applied to reduce the energy disorder by isolating isomer ICBA-tran3 from the as-synthesized ICBA-mixture. WBG perovskite solar cells with ICBA-tran3 show enhanced VOC by 60 mV, reduced VOC deficit of 0.5 V, and then a record stabilized power conversion efficiency of 18.5%. This work points out the importance of matching the charge transport layers in perovskite solar cells when the perovskites have a different composition and energy levels. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. Effect of band-gap narrowing on the built-in electric field in n-type silicon

    Science.gov (United States)

    Geist, J.; Lowney, J. R.

    1981-02-01

    A relation is derived to describe the change in the built-in electric field in an n-type semiconductor due to band tailing and carrier freeze-out, as well as band-gap narrowing. Recent numerical models of these various phenomena were used to illustrate the effect on heavily doped n-type silicon. While neither band-gap narrowing, band tailing, nor deionization alone is sufficient to explain the large decrease in the built-in electric field that has been inferred from experimental measurements, the combination of all three effects may be sufficient.

  12. Variability of bandgap and carrier mobility caused by edge defects in ultra-narrow graphene nanoribbons

    Science.gov (United States)

    Poljak, M.; Wang, K. L.; Suligoj, T.

    2015-06-01

    We report the results of multi-scale modeling of ultra-narrow graphene nanoribbons (GNRs) that combines atomistic non-equilibrium Green's function (NEGF) approach with semiclassical mobility modeling. The variability of the transport gap and carrier mobility caused by random edge defects is analyzed. We find that the variability increases as the GNR width is downscaled and that even the minimum variation of the total mobility reaches more than 100% compared to average mobility in edge-defected nanoribbons. It is shown that scattering by optical phonons exhibits significantly more variability than the acoustic, line-edge roughness and Coulomb scattering mechanisms. The simulation results demonstrate that sub-5 nm-wide nanoribbons offer no improvement over conventional bulk semiconductors, however, GNRs are comparable with sub-7 nm-thick silicon-on-insulator devices in terms of mobility-bandgap trade-off characteristics.

  13. Considerations of dopant-dependent bandgap narrowing for accurate device simulation in abrupt HBTs

    Institute of Scientific and Technical Information of China (English)

    Zhou Shouli; Xiong Deping; Qin Yali

    2009-01-01

    Heavy doping of the base in HBTs brings about a bandgap narrowing(BGN)effect,which modifies the intrinsic carrier density and disturbs the band offset,and thus leads to the change of the currents.Based on a thermionic-field-diffusion model that is used to the analyze the performance of all abrupt HBT with a heavydoped base,the conclusion is made that,although the BGN effect makes the currents obviously change due to the modification of the intrinsic carrier density,the band offsets disturbed by the BGN effect should also be taken into account in the analysis of the electrical characteristics of abrupt HBTs.In addition,the BGN effect changes the bias voltage for the onset of Kirk effects.

  14. Time-resolved measurements of charge carrier dynamics and optical nonlinearities in narrow-bandgap semiconductors

    Science.gov (United States)

    Olson, Benjamin Varberg

    All-optical time-resolved measurement techniques provide a powerful tool for investigating critical parameters that determine the performance of infrared photodetector and emitter semiconductor materials. Narrow-bandgap InAs/GaSb type-II superlattices (T2SLs) have shown great promise as a next generation source of these materials, due to superior intrinsic properties and versatility. Unfortunately, InAs/GaSb T2SLs are plagued by parasitic Shockley-Read-Hall recombination centers that shorten the carrier lifetime and limit device performance. Ultrafast pump-probe techniques and time-resolved differential transmission measurements are used here to demonstrate that Ga-free InAs/InAsSb T2SLs and InAsSb alloys do not have this same limitation and thus have significantly longer carrier lifetimes. Measurements at 77 K provided minority carrier lifetimes of 9 mus and 3 mus for an unintentionally doped mid-wave infrared (MWIR) InAs/InAsSb T2SL and InAsSb alloy, respectively; a two order of magnitude increase compared to the 90 ns minority carrier lifetime measured in a comparable MWIR InAs/GaSb T2SL. Through temperature-dependent lifetime measurements, the various carrier recombination processes are differentiated and the dominant mechanisms identified for each material. These results demonstrate that these Ga-free materials are viable options over InAs/GaSb T2SLs for potentially improved infrared photodetectors. In addition to carrier lifetimes, the drift and diffusion of excited charge carriers through the superlattice growth layers (i.e. vertical transport) directly affects the performance of photodetectors and emitters. Unfortunately, there is a lack of information pertaining to vertical transport, primarily due to difficulties in making measurements on thin growth layers and the need for non-standard measurement techniques. However, all-optical ultrafast techniques are successfully used here to directly measure vertical diffusion in MWIR InAs/GaSb T2SLs. By optically

  15. Statistical comparisons of data on band-gap narrowing in heavily doped silicon - Electrical and optical measurements

    Science.gov (United States)

    Bennett, H. S.; Wilson, C. L.

    1984-05-01

    A system of subroutines for iteratively reweighted least squares (IRLS) computations has been applied to the published measured and theoretical data on band-gap narrowing in heavily doped silicon. The data include electrical and optical measurements at room temperature, photoluminescence and optical measurements for temperatures below 35 K, and theoretical calculations at 300 and 0 K. The IRLS procedure allows a clear graphical comparison of the various experimental and theoretical data in band-gap narrowing to be made. The results are (1) band-gap changes determined by the optical absorption are consistent at both 300 K and at temperatures below 35 K with recent theoretical calculations, (2) the electrical and optical measurements are not consistent with each other, and (3) the low temperature optical absorption data and the photoluminescence data are not consistent with each other.

  16. Electrical band-gap narrowing in n- and p-type heavily doped silicon at 300 K

    Science.gov (United States)

    Van Cong, H.; Brunet, S.

    1986-09-01

    Based on previous results band-gap narrowing in heavily doped silicon at 300 K is investigated and expressed in terms of impurity size-and-doping effects. The results obtained for n- and p-type heavily doped silicon are compared with other theories and experiments.

  17. Semi-transparent polymer solar cells with excellent sub-bandgap transmission for third generation photovoltaics.

    Science.gov (United States)

    Beiley, Zach M; Christoforo, M Greyson; Gratia, Paul; Bowring, Andrea R; Eberspacher, Petra; Margulis, George Y; Cabanetos, Clément; Beaujuge, Pierre M; Salleo, Alberto; McGehee, Michael D

    2013-12-23

    Semi-transparent organic photovoltaics are of interest for a variety of photovoltaic applications, including solar windows and hybrid tandem photovoltaics. The figure shows a photograph of our semi-transparent solar cell, which has a power conversion efficiency of 5.0%, with an above bandgap transmission of 34% and a sub-bandgap transmission of 81%.

  18. Oxygen vacancy induced band-gap narrowing and enhanced visible light photocatalytic activity of ZnO.

    Science.gov (United States)

    Wang, Junpeng; Wang, Zeyan; Huang, Baibiao; Ma, Yandong; Liu, Yuanyuan; Qin, Xiaoyan; Zhang, Xiaoyang; Dai, Ying

    2012-08-01

    Oxygen vacancies in crystal have important impacts on the electronic properties of ZnO. With ZnO(2) as precursors, we introduce a high concentration of oxygen vacancies into ZnO successfully. The obtained ZnO exhibits a yellow color, and the absorption edge shifts to longer wavelength. Raman and XPS spectra reveal that the concentration of oxygen vacancies in the ZnO decreased when the samples are annealed at higher temperature in air. It is consistent with the theory calculation. The increasing of oxygen vacancies results in a narrowing bandgap and increases the visible light absorption of the ZnO. The narrowing bandgap can be confirmed by the enhancement of the photocurrent response when the ZnO was irradiated with visible light. The ZnO with oxygen vacancies are found to be efficient for photodecomposition of 2,4-dichlorophenol under visible light irradiation.

  19. Interface band gap narrowing behind open circuit voltage losses in Cu2ZnSnS4 solar cells

    DEFF Research Database (Denmark)

    Crovetto, Andrea; Palsgaard, Mattias Lau Nøhr; Gunst, Tue

    2017-01-01

    We present evidence that bandgap narrowing at the heterointerface may be a major cause of the large open circuit voltage deficit of Cu2ZnSnS4/CdS solar cells. Bandgap narrowing is caused by surface states that extend the Cu2ZnSnS4valence band into the forbidden gap. Those surface states are consi......We present evidence that bandgap narrowing at the heterointerface may be a major cause of the large open circuit voltage deficit of Cu2ZnSnS4/CdS solar cells. Bandgap narrowing is caused by surface states that extend the Cu2ZnSnS4valence band into the forbidden gap. Those surface states...... Zn to passivate those surface states. Focusing future research on Zn-based buffers is expected to significantly improve the open circuit voltage and efficiency of pure-sulfide Cu2ZnSnS4 solar cells....

  20. Band-gap narrowing in heavily doped silicon at 20 and 300 K studied by photoluminescence

    Science.gov (United States)

    Wagner, Joachim

    1985-07-01

    The band-gap shrinkage in heavily doped n- and p-type silicon is studied by photoluminescence both at low temperatures (20 K) and at room temperature (300 K). A line-shape analysis was performed to determine the indirect band-gap energy from the emission spectra. Within the experimental accuracy the same band-gap shift is observed at room temperature as at low temperature. The present results are compared with experimental data from other optical studies and with theoretical calculations.

  1. Band-gap narrowing and magnetic behavior of Ni-doped Ba(Ti0.875Ce0.125)O3 thin films

    Science.gov (United States)

    Zhou, Wenliang; Deng, Hongmei; Yu, Lu; Yang, Pingxiong; Chu, Junhao

    2015-11-01

    Band-gap narrowing and magnetic effects have been observed in a Ni-doped Ba(Ti0.875Ce0.125)O3 (BTC) thin film. Structural characterizations and microstructural analysis show that the as-prepared Ba(Ti0.75Ce0.125Ni0.125)O3-δ (BTCN) thin film exhibits a cubic perovskite structure with an average grain size of 25 nm. The Ce doping at the Ti-site results in an increasing perovskite volume to favour an O-vacancy-stabilized Ni2+ substitution. Raman spectroscopy, however, shows the cubic symmetry of crystalline structures is locally lowered by the presence of dopants, significantly deviating from the ideal Pm3m space group. Moreover, BTCN presents a narrowed band-gap, much smaller than that of BaTiO3 and BTC, due to new states of both the highest occupied molecular orbital and the lowest unoccupied molecular orbital in an electronic structure with the presence of Ni. Also, magnetic enhancement driven by co-doping has been confirmed in the films, which mainly stems from the exchange interaction of Ni2+ ions via an electron trapped in a bridging oxygen vacancy. These findings may open an avenue to discover and design optimal perovskite compounds for solar-energy devices and information storage.

  2. Defects induced luminescence and tuning of bandgap energy narrowing in ZnO nanoparticles doped with Li ions

    KAUST Repository

    Awan, Saif Ullah

    2014-08-28

    Microstructural and optical properties of Zn1-yLiyO (0.00 ≤y ≤0.10) nanoparticles are investigated. Li incorporation leads to substantial changes in the structural characterization. From micro-structural analysis, no secondary phases or clustering of Li was detected. Elemental maps confirmed homogeneous distribution of Li in ZnO. Sharp UV peak due to the recombination of free exciton and defects based luminescence broad visible band was observed. The transition from the conduction band to Zinc vacancy defect level in photoluminescence spectra is found at 518±2.5nm. The yellow luminescence was observed and attributed to Li related defects in doped samples. With increasing Li doping, a decrease in energy bandgap was observed in the range 3.26±0.014 to 3.17±0.018eV. The bandgap narrowing behavior is explained in terms of the band tailing effect due to structural disorder, carrier-impurities, carrier-carrier, and carrier-phonon interactions. Tuning of the bandgap energy in this class of wide bandgap semiconductor is very important for room temperature spintronics applications and optical devices. © 2014 AIP Publishing LLC.

  3. Semi-transparent polymer solar cells with excellent sub-bandgap transmission for third generation photovoltaics

    KAUST Repository

    Beiley, Zach M.

    2013-10-07

    Semi-transparent organic photovoltaics are of interest for a variety of photovoltaic applications, including solar windows and hybrid tandem photovoltaics. The figure shows a photograph of our semi-transparent solar cell, which has a power conversion efficiency of 5.0%, with an above bandgap transmission of 34% and a sub-bandgap transmission of 81%. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  4. Computer simulation and modeling of graded bandgap CuInSe{sub 2}/CdS based solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Dhingra, A.; Rothwarf, A. [Drexel Univ., Philadelphia, PA (United States). Dept. of Electrical and Computer Engineering

    1996-04-01

    This paper proposes the use of graded bandgap absorber material, to improve the low open-circuit voltage (V{sub oc}) seen in CuInSe{sub 2}/CdS solar cells, without sacrificing the short-circuit current density (J{sub sc}). It also proposes a p-i-n model for the CuInSe{sub 2}/CdS solar cell, where the intrinsic region is the graded bandgap CIS. Reflecting surfaces are provided at the p-i and n-i interfaces to trap the light in the narrow intrinsic region for maximum generation of electron and hole pairs (EHP`s). This optical confinement results in a 25--40% increase in the number of photons absorbed. An extensive numerical simulator was developed, which provides a 1-D self-consistent solution for Poisson`s equation and the two continuity equations for electrons and holes. This simulator was used to generate J-V curves to delineate the effect of different grading profiles on cell performance. The effects of a uniform bandgap, normal grading, reverse grading, and a low bandgap notch have been considered. Having established the inherent advantages to these grading profiles an optimal doubly graded structure is proposed. Replacing the thick CdS (2.42ev) layer assumed in the simulations with a wide gap semiconductor such as ZnO (3.35ev) increases all current densities by about 5 mA/cm{sup 2}, and increases the optimal calculated efficiency from 17.9% to roughly 21% for a doubly graded structure with a thickness of 1 {micro}m and bandgaps ranging from 1.3 eV to 1.5 eV.

  5. Selecting Semiconducting Single-Walled Carbon Nanotubes with Narrow Bandgap Naphthalene Diimide-Based Polymers

    NARCIS (Netherlands)

    Salazar-Rios, Jorge Mario; Gomulya, Widianta; Derenskyi, Vladimir; Yang, Jie; Bisri, Satria Zulkarnaen; Chen, Zhihua; Facchetti, Antonio; Loi, Maria Antonietta

    2015-01-01

    Noncovalent functionalization of carbon nanotubes by wrapping them using pi-conjugated polymers is one of the most promising techniques to sort, separate, and purify semiconducting nanotube species for applications in optoelectronic devices. However, wide energy bandgap polymers commonly used in thi

  6. A hard oxide semiconductor with a direct and narrow bandgap and switchable p-n electrical conduction.

    Science.gov (United States)

    Ovsyannikov, Sergey V; Karkin, Alexander E; Morozova, Natalia V; Shchennikov, Vladimir V; Bykova, Elena; Abakumov, Artem M; Tsirlin, Alexander A; Glazyrin, Konstantin V; Dubrovinsky, Leonid

    2014-12-23

    An oxide semiconductor (perovskite-type Mn2 O3 ) is reported which has a narrow and direct bandgap of 0.45 eV and a high Vickers hardness of 15 GPa. All the known materials with similar electronic band structures (e.g., InSb, PbTe, PbSe, PbS, and InAs) play crucial roles in the semiconductor industry. The perovskite-type Mn2 O3 described is much stronger than the above semiconductors and may find useful applications in different semiconductor devices, e.g., in IR detectors.

  7. Variable band-gap semiconductors as the basis of new 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, DF (Mexico)

    2009-09-15

    Some basic concepts related to variable band-gap absorbing semiconductors in solar cell structures, such as the associated quasi-electric field, will be discussed. The effects of this quasi-electric field upon the minority carrier drift-diffusion length and the back surface recombination velocity may induce a larger generated carrier collection at the junction with the corresponding increase of the illumination current density. It will also be shown that an additional improvement of the open-circuit voltage is possible when the band-gap is reduced within the space charge region so that the dark saturation current density is reduced there. Our estimation is that in the case of a solar cell where the band-gap is changed about 0.5 eV within the space charge region, an increase of the open-circuit voltage around 115 mV will be observed with respect to the single minimum band-gap absorbing material case. A similar band-gap variation in the bulk of the material will cause an increase of the minority carrier drift-diffusion length by a factor of 10 with respect to the single band-gap material. Therefore, based on these physical concepts, two possible structures with variable band-gap layers are proposed in order to have higher efficiencies than for cells without any band-gap grading. It will be shown that these concepts can be applied to II-VI, III-V chalcopyrite and even amorphous semiconductor solar cells. (author)

  8. Polymer solar cells and infrared light emitting diodes : Dual function low bandgap polymer

    NARCIS (Netherlands)

    Winder, C.; Mühlbacher, D.; Neugebauer, H.; Sariciftci, N.S.; Brabec, C.J.; Janssen, R.A.J.; Hummelen, J.C.

    2002-01-01

    Conjugated Polymers with a HOMO-LUMO transition <2eV, i.e. a low bandgap, respectively, have interesting and desired properties for some thin film optoelectronic devices like light emitting diodes and solar cells. In this contribution we present the implementation of the novel copolymer PTPTB,

  9. Polymer solar cells and infrared light emitting diodes : Dual function low bandgap polymer

    NARCIS (Netherlands)

    Winder, C.; Mühlbacher, D.; Neugebauer, H.; Sariciftci, N.S.; Brabec, C.J.; Janssen, R.A.J.; Hummelen, J.C.

    2002-01-01

    Conjugated Polymers with a HOMO-LUMO transition <2eV, i.e. a low bandgap, respectively, have interesting and desired properties for some thin film optoelectronic devices like light emitting diodes and solar cells. In this contribution we present the implementation of the novel copolymer PTPTB, consi

  10. Stable Low-Bandgap Pb-Sn Binary Perovskites for Tandem Solar Cells.

    Science.gov (United States)

    Yang, Zhibin; Rajagopal, Adharsh; Chueh, Chu-Chen; Jo, Sae Byeok; Liu, Bo; Zhao, Ting; Jen, Alex K-Y

    2016-10-01

    A low-bandgap (1.33 eV) Sn-based MA0.5 FA0.5 Pb0.75 Sn0.25 I3 perovskite is developed via combined compositional, process, and interfacial engineering. It can deliver a high power conversion efficiency (PCE) of 14.19%. Finally, a four-terminal all-perovskite tandem solar cell is demonstrated by combining this low-bandgap cell with a semitransparent MAPbI3 cell to achieve a high efficiency of 19.08%. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. Apparent bandgap shift in the internal quantum efficiency for solar cells with back reflectors

    Science.gov (United States)

    Steiner, M. A.; Perl, E. E.; Geisz, J. F.; Friedman, D. J.; Jain, N.; Levi, D.; Horner, G.

    2017-04-01

    We demonstrate that in solar cells with highly reflective back mirrors, the measured internal quantum efficiency exhibits a shift in bandgap relative to the measured external quantum efficiency. The shift arises from the fact that the measured reflectance at the front surface includes a superposition of waves reflecting from the front and back surfaces. We quantify the magnitude of the apparent shift and discuss the errors that can result in determination of quantities such as the photocurrent. Because of this apparent shift, it is important the bandgap be determined from the external quantum efficiency.

  12. Structure-property relationships of small bandgap conjugated polymers for solar cells.

    Science.gov (United States)

    Hellström, Stefan; Zhang, Fengling; Inganäs, Olle; Andersson, Mats R

    2009-12-01

    Conjugated polymers as electron donors in solar cells based on donor/acceptor combinations are of great interest, partly due to the possibility of converting solar light with a low materials budget. Six small bandgap polymers with optical bandgap ranging from 1.0-1.9 eV are presented in this paper. All polymers utilize an electron donor-acceptor-donor (DAD) segment in the polymer backbone, creating a partial charge-transfer, to decrease the bandgap. The design, synthesis and the optical characteristics as well as the solar cell characteristics of the polymers are discussed. The positions of the energy levels of the conjugated polymer relative to the electron acceptor are of significant importance and determine not only the driving force for exciton dissociation but also the maximum open-circuit voltage. This work also focuses on investigating the redox behavior of the described conjugated polymers and electron acceptors using square wave voltammetry. Comparing the electrochemical data gives important information of the structure-property relationships of the polymers.

  13. Incorporation of Furan into Low Band-Gap Polymers for Efficient Solar Cells

    KAUST Repository

    Woo, Claire H.

    2010-11-10

    The design, synthesis, and characterization of the first examples of furan-containing low band-gap polymers, PDPP2FT and PDPP3F, with substantial power conversion efficiencies in organic solar cells are reported. Inserting furan moieties in the backbone of the conjugated polymers enables the use of relatively small solubilizing side chains because of the significant contribution of the furan rings to overall polymer solubility in common organic solvents. Bulk heterojunction solar cells fabricated from furan-containing polymers and PC71BM as the acceptor showed power conversion efficiencies reaching 5.0%. © 2010 American Chemical Society.

  14. Effective absorption coefficient for graded band-gap semiconductors and the expected photocurrent density in 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)

    2009-01-15

    A simple model for the generation of carriers by photons incident on a (linearly) decreasing band-gap material, such as has been described in recent CIGS solar cells, is developed. The model can be generalized for different cases such as increasing band-gap grading or for having a more complex band-gap profile. The model developed for direct band semiconductors such as CIGS or AlGaAs allows us to define an effective absorption coefficient, so that the ideal photocurrent density can be calculated in a similar manner as for solar cells with non-graded band-gap materials. We show that this model gives completely different results as those expected from intuitive approaches for calculating this ideal photocurrent density. We also show that grading of the band-gap of the absorbing material in solar cells makes the photocurrent less sensitive to the total band-gap change, in such a way that the design of the band-gap variation can be more flexible in order to have other advantages such as higher built-in voltage or higher back surface field in the device structure. (author)

  15. Optimization of molecular organization and nanoscale morphology for high performance low bandgap polymer solar cells.

    Science.gov (United States)

    He, Ming; Wang, Mengye; Lin, Changjian; Lin, Zhiqun

    2014-04-21

    Rational design and synthesis of low bandgap (LBG) polymers with judiciously tailored HOMO and LUMO levels have emerged as a viable route to high performance polymer solar cells with power conversion efficiencies (PCEs) exceeding 10%. In addition to engineering the energy-level of LBG polymers, the photovoltaic performance of LBG polymer-based solar cells also relies on the device architecture, in particular the fine morphology of the photoactive layer. The nanoscale interpenetrating networks composed of nanostructured donor and acceptor phases are the key to providing a large donor-acceptor interfacial area for maximizing the exciton dissociation and offering a continuous pathway for charge transport. In this Review Article, we summarize recent strategies for tuning the molecular organization and nanoscale morphology toward an enhanced photovoltaic performance of LBG polymer-based solar cells.

  16. ZnO nanorod arrays for various low-bandgap polymers in inverted organic solar cells.

    Science.gov (United States)

    Ho, Ping-Yi; Thiyagu, Subramani; Kao, Shao-Hsuan; Kao, Chia-Yu; Lin, Ching-Fuh

    2014-01-07

    Due to the limited diffusion length of carriers in polymer solar cells (PSCs), the path of carriers is a crucial factor that determines the device performance. Zinc oxide nanorods (NRs) as the electron transport channel can reduce electron-hole recombination and transport the electron to the electrode efficiently for poly(3-hexylthiophene) (P3HT), but have been seldom demonstrated for low-bandgap polymers. Here we successfully applied ZnO NRs, which were grown via the hydrothermal method, as a platform to enhance PSC efficiency for various low-bandgap polymers. In order to assure that the nanorod morphology functioned properly for PSCs, the growth time, the concentration, and the resulting morphology were systematically investigated in depths. Such ZnO NRs were applied to different organic systems, resulting in the increase of the PCE for PBDTTT-C/PC71BM from 4.76% to 6.07% and PBDTTT-C-T/PC71BM from 5.40% to 7.34%. Through those experiments, we established a potentially universal and efficient ZnO NRs platform for various low-bandgap polymers to achieve high efficiency of inverted PSCs.

  17. Study of sub-bandgap states in polymer-fullerene solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Presselt, Martin; Herrmann, Felix; Seeland, Marco; Baerenklau, Maik; Engmann, Sebastian; Roesch, Roland; Shokhovets, Sviatoslav; Hoppe, Harald; Gobsch, Gerhard [Experimental Physics I, Institute of Physics and Institute of Micro- und Nanotechnologies, Ilmenau University of Technology (Germany); Beenken, Wichard J.D. [Theoretical Physics I, Institute of Physics, Ilmenau University of Technology (Germany)

    2010-07-01

    At present polymer-fullerene blends are widely used to build organic solar cells. The main contribution to their photocurrent originates from optical transitions between occupied states below the HOMO level and unoccupied states above the LUMO level of the polymer. In this work, we investigated the origin of states contributing to the optical absorption in the sub-bandgap spectral range and the resulting photocurrent in P3HT-PCBM bulk heterojunction solar cells. Photothermal deflection spectroscopy, temperature dependent external quantum efficiency, photoluminescence and electroluminescence as well as spectroscopic ellipsometry measurements have been carried out. Effects due to different P3HT-PCBM blending ratios and annealing temperatures have been studied. Two models are discussed to explain the experimental observations: optical transitions involving (a) disorder and/or defect related states, and (b) charge transfer complexes.

  18. Competitive behavior of photons contributing to junction voltage jump in narrow band-gap semiconductor multi-quantum-well laser diodes at lasing threshold

    Energy Technology Data Exchange (ETDEWEB)

    Feng, Liefeng, E-mail: fengliefeng@tju.edu.cn, E-mail: lihongru@nankai.edu.cn; Yang, Xiufang; Wang, Cunda; Yao, Dongsheng [Tianjin Key Laboratory of Low Dimensional Materials Physics and Preparing Technology, Faculty of Science, Tianjin University, Tianjin 300072 (China); Li, Yang [Business and Vocational College of Hainan, Haikou 570203 (China); Li, Ding; Hu, Xiaodong [Research Center for Wide Band Gap Semiconductors, State Key Laboratory for Artificial Microstructure and Mesoscopic Physics, School of Physics, Peking University, Beijing 100871 (China); Li, Hongru, E-mail: fengliefeng@tju.edu.cn, E-mail: lihongru@nankai.edu.cn [State Key Laboratory for Medicinal Chemistry and Biology, College of Pharmacy, Nankai University, Tianjin 300071 (China)

    2015-04-15

    The junction behavior of different narrow band-gap multi-quantum-well (MQW) laser diodes (LDs) confirmed that the jump in the junction voltage in the threshold region is a general characteristic of narrow band-gap LDs. The relative change in the 1310 nm LD is the most obvious. To analyze this sudden voltage change, the threshold region is divided into three stages by I{sub th}{sup l} and I{sub th}{sup u}, as shown in Fig. 2; I{sub th}{sup l} is the conventional threshold, and as long as the current is higher than this threshold, lasing exists and the IdV/dI-I plot drops suddenly; I{sub th}{sup u} is the steady lasing point, at which the separation of the quasi-Fermi levels of electron and holes across the active region (V{sub j}) is suddenly pinned. Based on the evolutionary model of dissipative structure theory, the rate equations of the photons in a single-mode LD were deduced in detail at I{sub th}{sup l} and I{sub th}{sup u}. The results proved that the observed behavior of stimulated emission suddenly substituting for spontaneous emission, in a manner similar to biological evolution, must lead to a sudden increase in the injection carriers in the threshold region, which then causes the sudden increase in the junction voltage in this region.

  19. Forward-bias capacitance and current measurements for determining lifetimes and band narrowing in p-n junction solar cells

    Science.gov (United States)

    Neugroschel, A.; Chen, P. J.; Pao, S. C.; Lindholm, F. A.

    1978-01-01

    A new method is described and illustrated for determining the minority-carrier diffusion length and lifetime in the base region of p-n junction solar cells. The method requires only capacitance measurements at the device terminals and its accuracy is estimated to be + or - 5%. It is applied to a set of silicon p-n junction devices and the values of the diffusion lengths agree with those obtained using the current response to X-ray excitation but disagree with those obtained by the OCVD method. The reasons for the relative inaccuracy of OCVD applied to silicon devices are discussed. The capacitance method includes corrections for a two-dimensional fringing effects which occur in small area devices. For a device having highly-doped base region and surface (emitter) layer, the method can be extended to enable the determination of material properties of the degenerately doped surface layer. These material properties include the phenomenological emitter lifetime and a measure of the energy band-gap narrowing in the emitter. An alternate method for determining the energy band-gap narrowing from temperature dependence of emitter current is discussed and demonstrated.

  20. Tunable narrow-bandpass filter based on an asymmetric photonic bandgap structure with a dual-mode liquid crystal.

    Science.gov (United States)

    Wang, Hsiao-Tsung; Timofeev, Ivan V; Chang, Kai; Zyryanov, Victor Ya; Lee, Wei

    2014-06-16

    A one-dimensional asymmetric photonic crystal with dual-frequency liquid crystal as a central defect layer was demonstrated. Such asymmetric structure was characterized by the dramatic increase in intensity of the electric field of light localized at the overlapped photonic bandgap edges, thereby enhancing the observed transmittance of the spectral windows originating from the defect layer. The defect layer was made of a dual-mode liquid crystal that exhibited not only electrical tunability and switchability but also optical bistability. Consequently, tunable and bistable defect modes can be realized in the photonic structure. This asymmetric photonic crystal structure is promising and should be further explored for photonic device applications.

  1. Compressed lead-based perovskites reaching optimal Shockley-Queisser bandgap with prolonged carrier lifetime

    CERN Document Server

    Liu, Gang; Gong, Jue; Yang, Wenge; Mao, Ho-kwang; Liu, Zhenxian; Schaller, Richard D; Zhang, Dongzhou; Xu, Tao

    2016-01-01

    Atomic structure of materials plays a decisive role in the light-matter interaction. Yet, despite its unprecedented progress, further efficiency boost of Lead-based organic-inorganic perovskite solar cells is hampered by its greater bandgap than the optimum value according to Shockley-Queisser limit. Here, we report the experimental achievement of bandgap narrowing in formamidinium lead triiodide from 1.489 to 1.337 eV by modulating the lattice constants under hydraulic compression, reaching the optimized bandgap for single-junction solar cells. Strikingly, such bandgap narrowing is accomplished with improved, instead of sacrificed carrier lifetime. More attractively, the narrowed bandgap is partially retainable after the release of pressure. This work opens a new dimension in basic science understanding of structural photonics and paves an alternative pathway towards more efficient photovoltaic materials.

  2. High-Performance Nonfullerene Polymer Solar Cells based on Imide-Functionalized Wide-Bandgap Polymers.

    Science.gov (United States)

    Fan, Baobing; Zhang, Kai; Jiang, Xiao-Fang; Ying, Lei; Huang, Fei; Cao, Yong

    2017-06-01

    High-performance nonfullerene polymer solar cells (PSCs) are developed by integrating the nonfullerene electron-accepting material 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2',3'-d']-s-indaceno[1,2-b:5,6-b']dithiophne) (ITIC) with a wide-bandgap electron-donating polymer PTzBI or PTzBI-DT, which consists of an imide functionalized benzotriazole (TzBI) building block. Detailed investigations reveal that the extension of conjugation can affect the optical and electronic properties, molecular aggregation properties, charge separation in the bulk-heterojunction films, and thus the overall photovoltaic performances. Single-junction PSCs based on PTzBI:ITIC and PTzBI-DT:ITIC exhibit remarkable power conversion efficiencies (PCEs) of 10.24% and 9.43%, respectively. To our knowledge, these PCEs are the highest efficiency values obtained based on electron-donating conjugated polymers consisting of imide-functionalized electron-withdrawing building blocks. Of particular interest is that the resulting device based on PTzBI exhibits remarkable PCE of 7% with the thickness of active layer of 300 nm, which is among the highest values of nonfullerene PSCs utilizing thick photoactive layer. Additionally, the device based on PTzBI:ITIC exhibits prominent stability, for which the PCE remains as 9.34% after thermal annealing at 130 °C for 120 min. These findings demonstrate the great promise of using this series of wide-bandgap conjugated polymers as electron-donating materials for high-performance nonfullerene solar cells toward high-throughput roll-to-roll processing technology. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. Demonstration of long minority carrier lifetimes in very narrow bandgap ternary InAs/GaInSb superlattices

    Science.gov (United States)

    Haugan, H. J.; Brown, G. J.; Olson, B. V.; Kadlec, E. A.; Kim, J. K.; Shaner, E. A.

    2015-09-01

    Minority carrier lifetimes in very long wavelength infrared (VLWIR) InAs/GaInSb superlattices (SLs) are reported using time-resolved microwave reflectance measurements. A strain-balanced ternary SL absorber layer of 47.0 Å InAs/21.5 Å Ga0.75In0.25Sb, corresponding to a bandgap of ˜50 meV, is found to have a minority carrier lifetime of 140 ± 20 ns at ˜18 K. This lifetime is extraordinarily long, when compared to lifetime values previously reported for other VLWIR SL detector materials. This enhancement is attributed to the strain-engineered ternary design, which offers a variety of epitaxial advantages and ultimately leads to a reduction of defect-mediated recombination centers.

  4. Efficient Semitransparent Solar Cells with High NIR Responsiveness Enabled by a Small-Bandgap Electron Acceptor.

    Science.gov (United States)

    Liu, Feng; Zhou, Zichun; Zhang, Cheng; Zhang, Jianyun; Hu, Qin; Vergote, Thomas; Liu, Feng; Russell, Thomas P; Zhu, Xiaozhang

    2017-06-01

    Inspired by the remarkable promotion of power conversion efficiency (PCE), commercial applications of organic photovoltaics (OPVs) can be foreseen in near future. One of the most promising applications is semitransparent (ST) solar cells that can be utilized in value-added applications such as energy-harvesting windows. However, the single-junction STOPVs utilizing fullerene acceptors show relatively low PCEs of 4%-6% due to the limited sunlight absorption because it is a dilemma that more photons need to be harvested in UV-vis-near-infrared (NIR) region to generate high photocurrent, which leads to the significant reduction of device transparency. This study describes the development of a new small-bandgap electron-acceptor material ATT-2, which shows a strong NIR absorption between 600 and 940 nm with an Eg(opt) of 1.32 eV. By combining with PTB7-Th, the as-cast OPVs yield PCEs of up to 9.58% with a fill factor of 0.63, an open-circuit voltage of 0.73 V, and a very high short-circuit current of 20.75 mA cm(-2) . Owing to the favorable complementary absorption of low-bangap PTB7-Th and small-bandgap ATT-2 in NIR region, the proof-of-concept STOPVs show the highest PCE of 7.7% so far reported for single-junction STOPVs with a high transparency of 37%. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. The correlation of open-circuit voltage with bandgap in amorphous silicon-based pin solar cells

    Science.gov (United States)

    Crandall, R. S.; Schiff, E. A.

    1996-01-01

    We briefly review the correlation of open-circuit voltages VOC with the bandgap of the intrinsic layer in amorphous silicon based pin solar cells. We discuss two mechanisms which limit VOC: intrinsic layer recombination, and the built-in potential VBI. In particular we discuss Li's proposal that the open-circuit voltages in higher bandgap cells (EG>1.9 eV) are VBI-limited. Based on computer simulations of pin solar cells we propose that VBI limitation occurs when the recombination limit to VOC exceeds the cell's field-reversal voltage VR. For a-Si:H based cells this field-reversal voltage occurs at about VBI-0.3 V. This proposal would account for the observation that VBI limitation occurs for VOC significantly smaller than VBI.

  6. Bandgap Tunability in Sb-Alloyed BiVO₄ Quaternary Oxides as Visible Light Absorbers for Solar Fuel Applications.

    Science.gov (United States)

    Loiudice, Anna; Ma, Jie; Drisdell, Walter S; Mattox, Tracy M; Cooper, Jason K; Thao, Timothy; Giannini, Cinzia; Yano, Junko; Wang, Lin-Wang; Sharp, Ian D; Buonsanti, Raffaella

    2015-11-01

    The challenge of fine compositional tuning and microstructure control in complex oxides is overcome by developing a general two-step synthetic approach. Antimony-alloyed bismuth vanadate, which is identified as a novel light absorber for solar fuel applications, is prepared in a wide compositional range. The bandgap of this quaternary oxide linearly decreases with the Sb content, in agreement with first-principles calculations.

  7. Bandgap narrowing in the layered oxysulfide semiconductor Ba3Fe2O5Cu2S2: Role of FeO2 layer

    Science.gov (United States)

    Han, Zhang; Shifeng, Jin; Liwei, Guo; Shijie, Shen; Zhiping, Lin; Xiaolong, Chen

    2016-02-01

    A new layered Cu-based oxychalcogenide Ba3Fe2O5Cu2S2 has been synthesized and its magnetic and electronic properties were revealed. Ba3Fe2O5Cu2S2 is built up by alternatively stacking [Cu2S2]2- layers and iron perovskite oxide [(FeO2)(BaO)(FeO2)]2- layers along the c axis that are separated by barium ions with Fe3+ fivefold coordinated by a square-pyramidal arrangement of oxygen. From the bond valence arguments, we inferred that in layered CuCh-based (Ch = S, Se, Te) compounds the +3 cation in perovskite oxide sheet prefers a square pyramidal site, while the lower valence cation prefers the square planar sites. The studies on susceptibility, transport, and optical reflectivity indicate that Ba3Fe2O5Cu2S2 is an antiferromagnetic semiconductor with a Néel temperature of 121 K and an optical bandgap of 1.03 eV. The measurement of heat capacity from 10 K to room temperature shows no anomaly at 121 K. The Debye temperature is determined to be 113 K. Theoretical calculations indicate that the conduction band minimum is predominantly contributed by O 2p and 3d states of Fe ions that antiferromagnetically arranged in FeO2 layers. The Fe 3d states are located at lower energy and result in a narrow bandgap in comparison with that of the isostructural Sr3Sc2O5Cu2S2. Project supported by the National Natural Science Foundation of China (Grant Nos. 51472266, 51202286, and 91422303), the Strategic Priority Research Program (B) of the Chinese Academy of Sciences (Grant No. XDB07020100) and the ICDD.

  8. Light and Electrically Induced Phase Segregation and Its Impact on the Stability of Quadruple Cation High Bandgap Perovskite Solar Cells.

    Science.gov (United States)

    Duong, The; Mulmudi, Hemant Kumar; Wu, YiLiang; Fu, Xiao; Shen, Heping; Peng, Jun; Wu, Nandi; Nguyen, Hieu T; Macdonald, Daniel; Lockrey, Mark; White, Thomas P; Weber, Klaus; Catchpole, Kylie

    2017-08-16

    Perovskite material with a bandgap of 1.7-1.8 eV is highly desirable for the top cell in a tandem configuration with a lower bandgap bottom cell, such as a silicon cell. This can be achieved by alloying iodide and bromide anions, but light-induced phase-segregation phenomena are often observed in perovskite films of this kind, with implications for solar cell efficiency. Here, we investigate light-induced phase segregation inside quadruple-cation perovskite material in a complete cell structure and find that the magnitude of this phenomenon is dependent on the operating condition of the solar cell. Under short-circuit and even maximum power point conditions, phase segregation is found to be negligible compared to the magnitude of segregation under open-circuit conditions. In accordance with the finding, perovskite cells based on quadruple-cation perovskite with 1.73 eV bandgap retain 94% of the original efficiency after 12 h operation at the maximum power point, while the cell only retains 82% of the original efficiency after 12 h operation at the open-circuit condition. This result highlights the need to have standard methods including light/dark and bias condition for testing the stability of perovskite solar cells. Additionally, phase segregation is observed when the cell was forward biased at 1.2 V in the dark, which indicates that photoexcitation is not required to induce phase segregation.

  9. Highly efficient luminescent solar concentrators based on earth-abundant indirect-bandgap silicon quantum dots

    Science.gov (United States)

    Meinardi, Francesco; Ehrenberg, Samantha; Dhamo, Lorena; Carulli, Francesco; Mauri, Michele; Bruni, Francesco; Simonutti, Roberto; Kortshagen, Uwe; Brovelli, Sergio

    2017-02-01

    Building-integrated photovoltaics is gaining consensus as a renewable energy technology for producing electricity at the point of use. Luminescent solar concentrators (LSCs) could extend architectural integration to the urban environment by realizing electrode-less photovoltaic windows. Crucial for large-area LSCs is the suppression of reabsorption losses, which requires emitters with negligible overlap between their absorption and emission spectra. Here, we demonstrate the use of indirect-bandgap semiconductor nanostructures such as highly emissive silicon quantum dots. Silicon is non-toxic, low-cost and ultra-earth-abundant, which avoids the limitations to the industrial scaling of quantum dots composed of low-abundance elements. Suppressed reabsorption and scattering losses lead to nearly ideal LSCs with an optical efficiency of η = 2.85%, matching state-of-the-art semi-transparent LSCs. Monte Carlo simulations indicate that optimized silicon quantum dot LSCs have a clear path to η > 5% for 1 m2 devices. We are finally able to realize flexible LSCs with performances comparable to those of flat concentrators, which opens the way to a new design freedom for building-integrated photovoltaics elements.

  10. Next Generation Solar Cells Based on Graded Bandgap Device Structures Utilising Rod-Type Nano-Materials

    Directory of Open Access Journals (Sweden)

    Imyhamy M. Dharmadasa

    2015-06-01

    Full Text Available Current solar cells under research and development utilise mainly one absorber layer limiting the photon harvesting capabilities. In order to develop next generation solar cells, research should move towards effective photon harvesting methods utilising low-cost solar energy materials. This will lead to reduce the $W−1 figure for direct solar energy conversion to electrical energy. In this work, a graded bandgap solar cell has been designed to absorb all photons from the UV, visible and IR regions. In addition, impurity PV effect and impact ionisation have been incorporated to enhance charge carrier creation within the same device. This new design has been experimentally tested using the most researched MOCVD grown GaAs/AlGaAs system, in order to confirm its validity. Devices with high Voc ~ 1175 mV and the highest possible FF ~ (0.85–0.87 have been produced, increasing the conversion efficiency to ~20% within only two growth runs. These devices were also experimentally tested for the existence of impurity PV effect and impact ionisation. The devices are PV active in complete darkness producing over 800 mV, Voc indicating the harvesting of IR radiation from the surroundings through impurity PV effect. The quantum efficiency measurements show over 140% signal confirming the contribution to PV action from impact ionisation. Since the concept is successfully proven, the low-cost and scalable electrodeposited semiconducting layers are used to produce graded bandgap solar cell structures. The utilisation of nano- and micro-rod type materials in graded bandgap devices are also presented and discussed in this paper. Preliminary work on glass/FTO/n-ZnS/n-CdS/n-CdTe/Au graded bandgap devices show 10%–12% efficient devices indicating extremely high Jsc values ~48 mA·cm−2, showing the high potential of these devices in achieving higher efficiencies. The detailed results on these low-cost and novel graded bandgap devices are presented in a separate

  11. High performance, high bandgap, lattice-mismatched, GaInP solar cells

    Science.gov (United States)

    Wanlass, Mark W.; Carapella, Jeffrey J.; Steiner, Myles A.

    2014-07-08

    High performance, high bandgap, lattice-mismatched, photovoltaic cells (10), both transparent and non-transparent to sub-bandgap light, are provided as devices for use alone or in combination with other cells in split spectrum apparatus or other applications.

  12. High performance, high bandgap, lattice-mismatched, GaInP solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Wanlass, Mark W; Carapella, Jeffrey J; Steiner, Myles A

    2016-11-01

    High performance, high bandgap, lattice-mismatched, photovoltaic cells (10), both transparent and non-transparent to sub-bandgap light, are provided as devices for use alone or in combination with other cells in split spectrum apparatus or other applications.

  13. Open-circuit voltage deficit, radiative sub-bandgap states, and prospects in quantum dot solar cells.

    Science.gov (United States)

    Chuang, Chia-Hao Marcus; Maurano, Andrea; Brandt, Riley E; Hwang, Gyu Weon; Jean, Joel; Buonassisi, Tonio; Bulović, Vladimir; Bawendi, Moungi G

    2015-05-13

    Quantum dot photovoltaics (QDPV) offer the potential for low-cost solar cells. To develop strategies for continued improvement in QDPVs, a better understanding of the factors that limit their performance is essential. Here, we study carrier recombination processes that limit the power conversion efficiency of PbS QDPVs. We demonstrate the presence of radiative sub-bandgap states and sub-bandgap state filling in operating devices by using photoluminescence (PL) and electroluminescence (EL) spectroscopy. These sub-bandgap states are most likely the origin of the high open-circuit-voltage (VOC) deficit and relatively limited carrier collection that have thus far been observed in QDPVs. Combining these results with our perspectives on recent progress in QDPV, we conclude that eliminating sub-bandgap states in PbS QD films has the potential to show a greater gain than may be attainable by optimization of interfaces between QDs and other materials. We suggest possible future directions that could guide the design of high-performance QDPVs.

  14. Thermoelectric properties of FeGa3-type narrow-bandgap intermetallic compounds Ru(Ga,In)3: Experimental and calculational studies

    Science.gov (United States)

    Takagiwa, Y.; Kitahara, K.; Matsubayashi, Y.; Kimura, K.

    2012-06-01

    The thermoelectric properties of polycrystalline binary narrow-bandgap intermetallic RuGa3 and RuIn3 compounds have been investigated in the temperature range from 373 K to 973 K. These compounds exhibit semiconductor-like transport properties with large Seebeck coefficients of -560 μV/K and 280 μV/K at 373 K for RuGa3 and RuIn3, respectively. The Seebeck coefficient of RuGa3 changed rapidly from large negative to large positive values around 500 K, which is consistent with our calculation based on the full-potential-linearized-augmented-plane-wave method. In contrast, RuIn3 is a p-type material at its operating temperature. The dimensionless figures of merit ZT of pure compounds reached maximum values of 0.13 and 0.17 at about 973 K and 773 K, respectively. The potential maximum ZT value was evaluated using the Boltzmann transport equation and can exceed unity by electron- or hole-doping for both compounds. By substituting Co for Ru in RuIn3, n-type thermoelectric materials (ZTmax = 0.10 at 473 K) were obtained. We suggest that ZT will be enhanced by further effective electron-doping.

  15. Thienopyrazine-based low-bandgap polymers for flexible polymer solar cells

    Science.gov (United States)

    Sensfuss, S.; Blankenburg, L.; Schache, H.; Shokhovets, S.; Erb, T.; Konkin, A.; Herasimovich, A.; Scheinert, S.; Shahid, M.; Sell, S.; Klemm, E.

    2010-09-01

    The optical gaps of the low-bandgap PPVs (PM-20, PM-19, PM-18) are decreased down to 1.6-1.7 eV compared with that of MDMO-PPV (2.2 eV). The best lateral hole mobility was determined to be 2.1 × 10-3 cm2/V s (PM-18) in field effect transistors and exceeds that of MDMO-PPV (poly-[ 2-methoxy-5-(3'^'.7'^'-dimethyloctyloxy)-1.4-phenylenevinylene], 8.5 × 10-4 cm2/V s). This allows to reduce the PCBM ([6.6]-phenyl-C61(71)-butanoic acid methyl ester) content in solar cell devices down to 1:2 w/w giving a better η_AM1.5 than for MDMO-PPV:[60]-PCBM cells (PM-19:[60]-PCBM 2.32% on ITO-PET, 2.86% on ITO glass). The charge transfer to PCBM as acceptor occurs quite normally and shows an effective charge separation using light-induced spin resonance spectroscopy (LESR). The [70]-PCBM-bullet signals are shifted to lower field related to those of [60]-PCBM-bullet and overlap more with the polaron signal of PM-19. The LESR g-factor components of [70]-PCBM-bullet are reported for the first time. The external quantum efficiency peak values achieve up to 42% at 350-400 nm and 26% at 640 nm (PM-19:[60]-PCBM).

  16. Alternative approaches of SiC & related wide bandgap materials in light emitting & solar cell applications

    Science.gov (United States)

    Wellmann, Peter; Syväjärvi, Mikael; Ou, Haiyan

    2014-03-01

    understanding the device performance. In relation to these, the surface pre-treatment and deposition technique can influence the reliability and electric field durability of the system, and relate to interface and near interface regions between the dielectric and semiconductor which can host electronic defects which change the surface potential, reduces mobility and enhance the recombination of charge carriers. At the end, materials for energy savings are critically needed. At the symposium ''Alternative approaches of SiC and related wide bandgap materials in light emitting and solar cell applications'', held at the E-MRS 2013 Spring meeting, 27-31 May, 2013 Strasbourg, France, a variety of concepts were presented. In this publication, a selection is presented that represents a range of issues from materials to reliability processing to system approaches. Acknowledgements: Technical support during preparation of the symposium program and proceedings by Saskia Schimmel is greatly acknowledged.

  17. Narrow bandgap host material for high quantum efficiency yellow phosphorescent organic light-emitting diodes doped with iridium(III) bis(4-phenylthieno[3,2-c]pyridine)acetylacetonate

    Energy Technology Data Exchange (ETDEWEB)

    Yook, Kyoung Soo; Lee, Jun Yeob, E-mail: leej17@skku.edu

    2015-05-15

    A narrow bandgap host material, 4,5-di(9H-carbazol-9-yl)phthalonitrile (2CzPN), was used as a bipolar host material to improve the device performances of yellow phosphorescent organic light-emitting diodes(PHOLEDs). The device performances of the yellow PHOLEDs were optimized at a low doping concentration of 1%. A low turn-on voltage of 3.0 V and high quantum efficiency of 19.3% were achieved using the 2CzPN host material and no efficiency roll-off of the device was observed up to 1000 cd/m{sup 2} compared with 25% of reference device. - Highlights: • High quantum efficiency in yellow phosphorescent organic light-emitting diodes. • Narrow bandgap host material with donor–acceptor structure for low driving voltage. • Low optimum doping concentration of 1% for high quantum efficiency and power efficiency.

  18. Low-bandgap mixed tin–lead iodide perovskite absorbers with long carrier lifetimes for all-perovskite tandem solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Zhao, Dewei; Yu, Yue; Wang, Changlei; Liao, Weiqiang; Shrestha, Niraj; Grice, Corey R.; Cimaroli, Alexander J.; Guan, Lei; Ellingson, Randy J.; Zhu, Kai; Zhao, Xingzhong; Xiong, Ren-Gen; Yan, Yanfa

    2017-03-01

    Tandem solar cells using only metal-halide perovskite sub-cells are an attractive choice for next-generation solar cells. However, the progress in developing efficient all-perovskite tandem solar cells has been hindered by the lack of high-performance low-bandgap perovskite solar cells. Here, we report efficient mixed tin-lead iodide low-bandgap (~1.25 eV) perovskite solar cells with open-circuit voltages up to 0.85 V and over 70% external quantum efficiencies in the infrared wavelength range of 700-900 nm, delivering a short-circuit current density of over 29 mA cm-2 and demonstrating suitability for bottom-cell applications in all-perovskite tandem solar cells. Our low-bandgap perovskite solar cells achieve a maximum power conversion efficiency of 17.6% and a certified efficiency of 17.01% with a negligible current-voltage hysteresis. When mechanically stacked with a ~1.58 eV bandgap perovskite top cell, our best all-perovskite 4-terminal tandem solar cell shows a steady-state efficiency of 21.0%.

  19. Photon absorption and photocurrent in solar cells below semiconductor bandgap due to electron photoemission from plasmonic nanoantennas

    DEFF Research Database (Denmark)

    Novitsky, Andrey; Uskov, Alexander; Gritti, Claudia;

    2014-01-01

    We model the electron photoemission frommetal nanoparticles into a semiconductor in a Schottky diode with a conductive oxide electrode hosting the nanoparticles. We show that plasmonic effects in the nanoparticles lead to a substantial enhancement in photoemission compared with devices with conti....... Such structure can form the dais of the development of plasmonic photoemission enhanced solar cells....... with continuous metal films. Optimally designed metal nanoparticles can provide an effectivemechanismfor the photon absorption in the infrared range below the semiconductor bandgap, resulting in the generation of a photocurrent in addition to the photocurrent from band-to-band absorption in a semiconductor...

  20. Bandgap tailoring of in-situ nitrogen-doped TiO₂ sputtered films intended for electrophotocatalytic applications under solar light

    Energy Technology Data Exchange (ETDEWEB)

    Delegan, N.; El Khakani, M. A., E-mail: elkhakani@emt.inrs.ca [Institut National de la Recherche Scientifique, Centre Énergie, Matériaux et Télécommunications, 1650, Boulevard Lionel-Boulet, Varennes, Québec J3X-1S2 (Canada); Daghrir, R.; Drogui, P. [Institut National de la Recherche Scientifique, Centre Eau, Terre et Environnement, 490 Rue de la Couronne, Québec G1K-9A9 (Canada)

    2014-10-21

    We report on a reactive RF-sputtering process permitting the in-situ nitrogen doping of TiO₂ films in order to shift their photoactivity from UV to visible range. By carefully controlling the relative nitrogen-to-argon mass flow rate ratio (within the 0%–25% range) in the sputter deposition chamber, TiO₂:N films were grown with nitrogen contents ranging from 0 to 6.2 at. %, as determined by high-resolution X-ray spectroscopy measurements. A systematic investigation of the crystalline structure of the TiO₂:N films, as a function of their N content, revealed that low N contents (0.2–0.3 at. %) induce crystallization in the rutile phase while higher N contents (≥1.4 at. %) were accompanied with the recovery of the anatase structure with an average crystallite size of ~35 nm. By using both UV-Vis absorption and spectroscopic ellipsometry measurements, we were able to quantitatively determine the bandgap (E{sub g}) variation of the TiO₂:N films as a function of their N content. Thus, we have demonstrated that the E{sub g} of the TiO₂:N films effectively narrows from 3.2 eV down to a value as low as ~2.3 eV for the optimal N doping concentration of 3.4 at. % (higher N incorporation does not translate into further red shifting of the TiO₂:N films' E{sub g}). The photoactivity of the TiO₂:N films under visible light was confirmed through electro-photocatalytic decomposition of chlortetracycline (CTC, an emerging water pollutant) under standard 1.5AM solar radiation. Thus, CTC degradation efficiencies of up to 98% were achieved with 2 hours process cycles under simulated solar light. Moreover, the electro-photocatalytic performance of the TiO₂:N films is shown to be directly correlated to their optoelectronic properties (namely their bandgap narrowing).

  1. Small bandgap polymers for organic solar cells (polymer material development in the last 5 years)

    NARCIS (Netherlands)

    Kroon, Renee; Lenes, Martijn; Hummelen, Jan C.; Blom, Paul W.M.; Boer, Bert de

    2008-01-01

    During the last decade the field of polymer photovoltaics has seen a tremendous improvement in both device efficiency and understanding of the underlying physical processes. One has come to a point in which the prototypical large bandgap material system P3HT:PCBM is nearing optimal device performanc

  2. Tensile strain induced narrowed bandgap of TiO{sub 2} films: Utilizing the two-way shape memory effect of TiNiNb substrate and in-situ mechanical bending

    Energy Technology Data Exchange (ETDEWEB)

    Du, Minshu, E-mail: dms1223@126.com [Department of Materials Science and Engineering, China University of Petroleum at Beijing, Beijing, 102249 (China); Center for Electrochemistry, Department of Chemistry, The University of Texas at Austin, Austin, Texas, 78712 (United States); Cui, Lishan; Wan, Qiong [Department of Materials Science and Engineering, China University of Petroleum at Beijing, Beijing, 102249 (China)

    2016-05-15

    Graphical abstract: - Highlights: • Imposed tensile strain to anatase TiO{sub 2} nanofilm by using the two-way shape memory effect of NiTiNb substrate. • Imposed tensile strain to rutile TiO{sub 2} thin film by in-situ mechanical bending. • Tauc plot based on the PEC-tested auction spectrum was utilized to precisely determine the bandgap of TiO{sub 2}. • Tensile strain narrowed the bandgap of anatase TiO{sub 2} by 60 meV and rutile TiO{sub 2} by 70 meV. • Tensile strain contributes to a 1.5 times larger photocurrent for the water oxidation reaction. - Abstract: Elastic strain is one of the methods to alter the band gap of semiconductors. However, relevant experimental work is limited due to the difficulty in imposing strain. Two new methods for imposing tensile strain to TiO{sub 2} film were introduced here. One is by utilizing the two-way shape memory effect of NiTiNb substrate, and the other method is in-situ mechanical bending. The former method succeeded in imposing 0.4% tensile strain to anatase TiO{sub 2} nanofilm, and strain narrowed the bandgap of TiO{sub 2} by 60 meV. The latter method enabled rutile TiO{sub 2} thin film under the 0.5% biaxially tensile-strained state, which contributes to a narrowed bandgap with ΔE{sub g} of 70 meV. Also, photocurrents of both strained TiO{sub 2} films increased by 1.5 times compared to the strain-free films, which indirectly verified the previous DFT prediction proposed by Thulin and Guerra in 2008 that tensile strain could improve the mobility and separation of photo-excite carriers.

  3. The correlation of open-circuit voltage with bandgap in amorphous silicon-based {ital pin} solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Crandall, R.S. [National Renewable Energy Laboratory, Golden, Colorado 80401 (United States); Schiff, E.A. [Department of Physics, Syracuse University, Syracuse, New York 13244-1130 (United States)

    1996-01-01

    We briefly review the correlation of open-circuit voltages {ital V}{sub OC} with the bandgap of the intrinsic layer in amorphous silicon based {ital pin} solar cells. We discuss two mechanisms which limit {ital V}{sub OC}: intrinsic layer recombination, and the built-in potential {ital V}{sub BI}. In particular we discuss Li{close_quote}s proposal that the open-circuit voltages in higher bandgap cells ({ital E}{sub G}{gt}1.9 eV) are {ital V}{sub BI}-limited. Based on computer simulations of {ital pin} solar cells we propose that {ital V}{sub BI} limitation occurs when the recombination limit to {ital V}{sub OC} exceeds the cell{close_quote}s field-reversal voltage {ital V}{sub R}. For {ital a}-Si:H based cells this field-reversal voltage occurs at about {ital V}{sub BI}-0.3 V. This proposal would account for the observation that {ital V}{sub BI} limitation occurs for {ital V}{sub OC} significantly smaller than {ital V}{sub BI}. {copyright} {ital 1996 American Institute of Physics.}

  4. Using cyclopenta[2,1-b:3,4-c']dithiophene-4-one as a building block for low-bandgap conjugated copolymers applied in solar cells.

    Science.gov (United States)

    Zhang, Wei; Cao, Jiamin; Liu, Ying; Xiao, Zuo; Zhu, Weiguo; Zuo, Qiqun; Ding, Liming

    2012-09-26

    A novel electron-accepting unit cyclopenta[2,1-b:3,4-c']dithiophene-4-one (CPDTO-c'), which is an isomer of CPDTO-b' was developed. CPDTO-c' can be incorporated into the D-A backbone through 5, 7 positions. The 2 position of CPDTO-c' can be easily functionalized with an electron-withdrawing chain. By copolymerizing CPDTO-c' with four different donor units: benzo[1,2-b:4,5-b']dithiophene (BDT), dithieno[3,2-b:2',3'-d]silole (DTS), carbazole, and fluorene, four new conjugated copolymers P1-P4 were obtained. All these polymers have good solubility and low-lying HOMO energy levels (-5.41 ∼ -5.92 eV). Among them, P1 and P2 exhibit broad absorption and narrow optical bandgaps of 1.91 and 1.72 eV, respectively. Solar cells based on P1/PC(71) BM afforded a PCE up to 2.72% and a high V(oc) up to ∼0.9 V.

  5. How to design low bandgap polymers for highly efficient organic solar cells

    OpenAIRE

    Tao Xu; Luping Yu

    2014-01-01

    Organic photovoltaic cells are promising in terms of their light weight, mechanically flexibility, ease of processing and low cost. Establishing a predictive understanding between the chemical structures and physical properties of polymers is still challenging, and continuous effort is needed to progress toward full commercialization. In this review, recent progress in polymer/fullerene systems is highlighted and four synthetic principles are summarized to engineer the bandgap and tune the en...

  6. How to design low bandgap polymers for highly efficient organic solar cells

    Directory of Open Access Journals (Sweden)

    Tao Xu

    2014-01-01

    Full Text Available Organic photovoltaic cells are promising in terms of their light weight, mechanically flexibility, ease of processing and low cost. Establishing a predictive understanding between the chemical structures and physical properties of polymers is still challenging, and continuous effort is needed to progress toward full commercialization. In this review, recent progress in polymer/fullerene systems is highlighted and four synthetic principles are summarized to engineer the bandgap and tune the energy levels and the solubility of the targeted polymers.

  7. Solar-light photocatalytic disinfection using crystalline/amorphous low energy bandgap reduced TiO2.

    Science.gov (United States)

    Kim, Youngmin; Hwang, Hee Min; Wang, Luyang; Kim, Ikjoon; Yoon, Yeoheung; Lee, Hyoyoung

    2016-04-28

    A generation of reactive oxygen species (ROS) from TiO2 under solar light has been long sought since the ROS can disinfect organic pollutants. We found that newly developed crystalline/amorphous reduced TiO2 (rTiO2) that has low energy bandgap can effectively generate ROS under solar light and successfully remove a bloom of algae. The preparation of rTiO2 is a one-pot and mass productive solution-process reduction using lithium-ethylene diamine (Li-EDA) at room temperature. Interestingly only the rutile phase of TiO2 crystal was reduced, while the anatase phase even in case of both anatase/rutile phased TiO2 was not reduced. Only reduced TiO2 materials can generate ROS under solar light, which was confirmed by electron spin resonance. Among the three different types of Li-EDA treated TiO2 (anatase, rutile and both phased TiO2), the both phased rTiO2 showed the best performance to produce ROS. The generated ROS effectively removed the common green algae Chlamydomonas. This is the first report on algae degradation under solar light, proving the feasibility of commercially available products for disinfection.

  8. Conversion efficiency limits and bandgap designs for multi-junction solar cells with internal radiative efficiencies below unity.

    Science.gov (United States)

    Zhu, Lin; Mochizuki, Toshimitsu; Yoshita, Masahiro; Chen, Shaoqiang; Kim, Changsu; Akiyama, Hidefumi; Kanemitsu, Yoshihiko

    2016-05-16

    We calculated the conversion-efficiency limit ηsc and the optimized subcell bandgap energies of 1 to 5 junction solar cells without and with intermediate reflectors under 1-sun AM1.5G and 1000-sun AM1.5D irradiations, particularly including the impact of internal radiative efficiency (ηint) below unity for realistic subcell materials on the basis of an extended detailed-balance theory. We found that the conversion-efficiency limit ηsc significantly drops when the geometric mean ηint* of all subcell ηint in the stack reduces from 1 to 0.1, and that ηsc degrades linearly to logηint* for ηint* below 0.1. For ηint*<0.1 differences in ηsc due to additional intermediate reflectors became very small if all subcells are optically thick for sun light. We obtained characteristic optimized bandgap energies, which reflect both ηint* decrease and AM1.5 spectral gaps. These results provide realistic efficiency targets and design principles.

  9. Graded-Bandgap Solar Cells Using All-Electrodeposited ZnS, CdS and CdTe Thin-Films

    Directory of Open Access Journals (Sweden)

    Obi K. Echendu

    2015-05-01

    Full Text Available A 3-layer graded-bandgap solar cell with glass/FTO/ZnS/CdS/CdTe/Au structure has been fabricated using all-electrodeposited ZnS, CdS and CdTe thin layers. The three semiconductor layers were electrodeposited using a two-electrode system for process simplification. The incorporation of a wide bandgap amorphous ZnS as a buffer/window layer to form glass/FTO/ZnS/CdS/CdTe/Au solar cell resulted in the formation of this 3-layer graded-bandgap device structure. This has yielded corresponding improvement in all the solar cell parameters resulting in a conversion efficiency >10% under AM1.5 illumination conditions at room temperature, compared to the 8.0% efficiency of a 2-layer glass/FTO/CdS/CdTe/Au reference solar cell structure. These results demonstrate the advantages of the multi-layer graded-bandgap device architecture over the conventional 2-layer structure. In addition, they demonstrate the effective application of the two-electrode system as a simplification to the conventional three-electrode system in the electrodeposition of semiconductors with the elimination of the reference electrode as a possible impurity source.

  10. High-Pressure Study of Perovskite-Like Organometal Halide: Band-Gap Narrowing and Structural Evolution of [NH 3 -(CH 2 )4 -NH3 ]CuCl4

    Energy Technology Data Exchange (ETDEWEB)

    Li, Qian; Li, Shourui; Wang, Kai; Quan, Zewei; Meng, Yue; Zou, Bo

    2017-01-10

    Searching for nontoxic and stable perovskite-like alternatives to lead-based halide perovskites for photovoltaic application is one urgent issue in photoelectricity science. Such exploration inevitably requires an effective method to accurately control both the crystalline and electronic structures. This work applies high pressure to narrow the band gap of perovskite-like organometal halide, [NH3-(CH2)4-NH3]CuCl4 (DABCuCl4), through the crystalline-structure tuning. The band gap keeps decreasing below ~12 GPa, involving the shrinkage and distortion of CuCl42–. Inorganic distortion determines both band-gap narrowing and phase transition between 6.4 and 10.5 GPa, and organic chains function as the spring cushion, evidenced by the structural transition at ~0.8 GPa. The supporting function of organic chains protects DABCuCl4 from phase transition and amorphization, which also contributes to the sustaining band-gap narrowing. This work combines crystal structure and macroscopic property together and offers new strategies for the further design and synthesis of hybrid perovskite-like alternatives.

  11. A hot-electron thermophotonic solar cell demonstrated by thermal up-conversion of sub-bandgap photons.

    Science.gov (United States)

    Farrell, Daniel J; Sodabanlu, Hassanet; Wang, Yunpeng; Sugiyama, Masakazu; Okada, Yoshitaka

    2015-11-06

    The direct conversion of solar energy to electricity can be broadly separated into two main categories: photovoltaics and thermal photovoltaics, where the former utilizes gradients in electrical potential and the latter thermal gradients. Conventional thermal photovoltaics has a high theoretical efficiency limit (84%) but in practice cannot be easily miniaturized and is limited by the engineering challenges of sustaining large (>1,000 K) temperature gradients. Here we show a hot-carrier-based thermophotonic solar cell, which combines the compact nature of photovoltaic devices with the potential to reach the high-efficiency regime of thermal photovoltaics. In the device, a thermal gradient of 500 K is established by hot electrons, under Stokes illumination, rather than by raising the temperature of the material itself. Under anti-Stokes (sub-bandgap) illumination we observe a thermal gradient of ∼20 K, which is maintained by steady-state Auger heating of carriers and corresponds to a internal thermal up-conversion efficiency of 30% between the collector and solar cell.

  12. Tunable Narrow Band Gap Absorbers For Ultra High Efficiency Solar Cells

    Energy Technology Data Exchange (ETDEWEB)

    Bedair, Salah M. [North Carolina State Univ., Raleigh, NC (United States); Hauser, John R. [North Carolina State Univ., Raleigh, NC (United States); Elmasry, Nadia [North Carolina State Univ., Raleigh, NC (United States); Colter, Peter C. [North Carolina State Univ., Raleigh, NC (United States); Bradshaw, G. [North Carolina State Univ., Raleigh, NC (United States); Carlin, C. Z. [North Carolina State Univ., Raleigh, NC (United States); Samberg, J. [North Carolina State Univ., Raleigh, NC (United States); Edmonson, Kenneth [Spectrolab, Inc., Sylmar, CA (United States)

    2012-07-31

    We report on a joint research program between NCSU and Spectrolab to develop an upright multijunction solar cell structure with a potential efficiency exceeding the current record of 41.6% reported by Spectrolab. The record efficiency Ge/GaAs/InGaP triple junction cell structure is handicapped by the fact that the current generated by the Ge cell is much higher than that of both the middle and top cells. We carried out a modification of the record cell structure that will keep the lattice matched condition and allow better matching of the current generated by each cell. We used the concept of strain balanced strained layer superlattices (SLS), inserted in the i-layer, to reduce the bandgap of the middle cell without violating the desirable lattice matched condition. For the middle GaAs cell, we have demonstrated an n-GaAs/i-(InGaAs/GaAsP)/p-GaAs structure, where the InxGa1-xAs/GaAs1-yPy SLS is grown lattice matched to GaAs and with reduced bandgap from 1.43 eV to 1.2 eV, depending upon the values of x and y.

  13. Development of a Wide Bandgap Cell for Thin Film Tandem Solar Cells: Final Technical Report, 6 November 2003 - 5 January 2007

    Energy Technology Data Exchange (ETDEWEB)

    Shafarman, W.; McCandless, B.

    2008-08-01

    The objective of this research program was to develop approaches for a transparent wide-bandgap cell to be used in a thin-film tandem polycrystalline solar cell that can ultimately attain 25% efficiency. Specific goals included the research and development of Cu(InGa)(SeS)2 and Cd1-xZnxTe alloys with a bandgap from 1.5 to 1.8 eV, demonstrating the potential of a 15% cell efficiency with a transparent contact, and supporting the High Performance PV Program. This Final Report presents results that emphasize the 3rd phase of the program.

  14. Synthesis and Characterization of Quinoxaline-Based Low-Bandgap Copolymers for Bulk Heterojunction Solar Cells

    Science.gov (United States)

    Lee, Yoonkyoo; Jo, Won Ho

    2011-03-01

    A series of low-bandgap alternating copolymers consisting of quinoxaline derivatives and electron-donating carbazole or fluorene were synthesized via the Suzuki coupling reaction. For the purpose to improve the molecular packing of polymer chains and to enhance the charge carrier mobility in the packing direction, a new quinoxaline derivative, 5,8-dithien-2-yl-dibenzophenazine which has perfectly planar polycyclic structure, was synthesized and introduced as a new building block for alternating copolymers instead of frequently-used 5,8-dithien-2-yl-2,3-diphenylquinoxaline. The use of planar quinoxaline derivative exhibited better optical, electrochemical, and structural properties of the resulting copolymers as compared to those of polymers with less planar quinoxaline derivatives. Charge transport and photovoltaic properties of these two classes of copolymers are compared and discussed.

  15. Fabrication of Efficient Low-Bandgap Perovskite Solar Cells by Combining Formamidinium Tin Iodide with Methylammonium Lead Iodide.

    Science.gov (United States)

    Liao, Weiqiang; Zhao, Dewei; Yu, Yue; Shrestha, Niraj; Ghimire, Kiran; Grice, Corey R; Wang, Changlei; Xiao, Yuqing; Cimaroli, Alexander J; Ellingson, Randy J; Podraza, Nikolas J; Zhu, Kai; Xiong, Ren-Gen; Yan, Yanfa

    2016-09-28

    Mixed tin (Sn)-lead (Pb) perovskites with high Sn content exhibit low bandgaps suitable for fabricating the bottom cell of perovskite-based tandem solar cells. In this work, we report on the fabrication of efficient mixed Sn-Pb perovskite solar cells using precursors combining formamidinium tin iodide (FASnI3) and methylammonium lead iodide (MAPbI3). The best-performing cell fabricated using a (FASnI3)0.6(MAPbI3)0.4 absorber with an absorption edge of ∼1.2 eV achieved a power conversion efficiency (PCE) of 15.08 (15.00)% with an open-circuit voltage of 0.795 (0.799) V, a short-circuit current density of 26.86(26.82) mA/cm(2), and a fill factor of 70.6(70.0)% when measured under forward (reverse) voltage scan. The average PCE of 50 cells we have fabricated is 14.39 ± 0.33%, indicating good reproducibility.

  16. Influence of grain boundary modification on limited performance of wide bandgap Cu(In,Ga)Se2 solar cells

    Science.gov (United States)

    Raghuwanshi, M.; Cadel, E.; Pareige, P.; Duguay, S.; Couzinie-Devy, F.; Arzel, L.; Barreau, N.

    2014-07-01

    The reason why so-called wide-bandgap CuIn1-xGaxSe2 (CIGSe with x > 0.4) based solar cells show hindered performance compared with theoretical expectations is still a matter of debate. In the present Letter, atom probe tomography studies of CuIn1-xGaxSe2 polycrystalline thin films with x varying from 0 to 1 are reported. These investigations confirm that the grain boundaries (GBs) of low gallium containing (x CIGSe layers are Cu-depleted compared with grains interior (GI). In contrast, it is observed that the GBs of widest band gap CIGSe films (x > 0.8) are Cu-enriched compared with GI. For intermediate gallium contents (0.4 < x < 0.8), both types of GBs are detected. This threshold value of 0.4 surprisingly coincides with solar cells output voltage deviation from theoretical expectations, which suggests modifications of GBs properties could participate in the loss of photovoltaic performance.

  17. Influence of grain boundary modification on limited performance of wide bandgap Cu(In,Ga)Se{sub 2} solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Raghuwanshi, M., E-mail: mohit.raghuwanshi@etu.univ-rouen.fr; Cadel, E.; Pareige, P.; Duguay, S. [Groupe de Physique des Materiaux (GPM), UMR 6634 CNRS, Université et INSA de Rouen, Avenue de l' Universite BP 12, 76801 Saint Etienne du Rouvray (France); Couzinie-Devy, F.; Arzel, L.; Barreau, N. [Institut des Materiaux Jean Rouxel (IMN), UMR 6502 CNRS, Université de Nantes, 2 rue de la Houssiniere BP 32229, 44322 Nantes cedex 3 (France)

    2014-07-07

    The reason why so-called wide-bandgap CuIn{sub 1−x}Ga{sub x}Se{sub 2} (CIGSe with x > 0.4) based solar cells show hindered performance compared with theoretical expectations is still a matter of debate. In the present Letter, atom probe tomography studies of CuIn{sub 1−x}Ga{sub x}Se{sub 2} polycrystalline thin films with x varying from 0 to 1 are reported. These investigations confirm that the grain boundaries (GBs) of low gallium containing (x < 0.4) CIGSe layers are Cu-depleted compared with grains interior (GI). In contrast, it is observed that the GBs of widest band gap CIGSe films (x > 0.8) are Cu-enriched compared with GI. For intermediate gallium contents (0.4 < x < 0.8), both types of GBs are detected. This threshold value of 0.4 surprisingly coincides with solar cells output voltage deviation from theoretical expectations, which suggests modifications of GBs properties could participate in the loss of photovoltaic performance.

  18. Fabrication of Efficient Low-Bandgap Perovskite Solar Cells by Combining Formamidinium Tin Iodide with Methylammonium Lead Iodide

    Energy Technology Data Exchange (ETDEWEB)

    Liao, Weiqiang; Zhao, Dewei; Yu, Yue; Shrestha, Niraj; Ghimire, Kiran; Grice, Corey R.; Wang, Changlei; Xiao, Yuqing; Cimaroli, Alexander J.; Ellingson, Randy J.; Podraza, Nikolas J.; Zhu, Kai; Xiong, Ren-Gen; Yan, Yanfa

    2016-09-28

    Mixed tin (Sn)-lead (Pb) perovskites with high Sn content exhibit low bandgaps suitable for fabricating the bottom cell of perovskite-based tandem solar cells. In this work, we report on the fabrication of efficient mixed Sn-Pb perovskite solar cells using precursors combining formamidinium tin iodide (FASnI3) and methylammonium lead iodide (MAPbI3). The best-performing cell fabricated using a (FASnI3)0.6(MAPbI3)0.4 absorber with an absorption edge of ~1.2 eV achieved a power conversion efficiency (PCE) of 15.08 (15.00)% with an open-circuit voltage of 0.795 (0.799) V, a short-circuit current density of 26.86(26.82) mA/cm2, and a fill factor of 70.6(70.0)% when measured under forward (reverse) voltage scan. The average PCE of 50 cells we have fabricated is 14.39 +/- 0.33%, indicating good reproducibility.

  19. Effect of Molecular Weight and Processing Additive on the Performance of Low Bandgap Polymer Solar Cells

    Institute of Scientific and Technical Information of China (English)

    赵晓礼; 唐浩为; 杨大磊; 李慧; 徐文涛; 尹丽; 杨小牛

    2012-01-01

    In this work, we synthesized a low bandgap polymer polysilole(-2,6-diyl-alt-5-octylthieno[3,4-c]pyrrole-4,6- dione) (PDTSTPD) with different molecular weights (Mn). The devices based on PDTSTPD/PC71BM composite are prepared and the dependence of power conversion efficiency (PCE) of the devices on the M,1 of conjugated poly- mers is addressed. We found the hole mobility of PDTSTPD is dependent on the Mn of the polymer, which should be the main reason contributing to the drastic difference of device performance, i.e. the PCE of the device using 10 kDa polymer is only 0.52%, in contrast to 2.3% for 24 kDa polymer device. This PCE data is then further improved to 5.0% via using 1,8-diiodoctane as processing additive to achieve an optimized morphology for the photoactive layer with an appropriate length-scale of phase separation for both exciton dissociation and charge transportation.

  20. Narrow-bandwidth solar upconversion: design principles, efficiency limits, and case studies

    CERN Document Server

    Briggs, Justin A; Dionne, Jennifer A

    2013-01-01

    We employ a detailed balance approach to model a single-junction solar cell with a realistic narrow-band, non-unity-quantum-yield upconverter. As upconverter bandwidths are increased from 0 to 0.5 eV, maximum cell efficiencies increase from the Shockley-Queisser limit of 30.58% to over 43%. Such efficiency enhancements are calculated for upconverters with near-infrared spectral absorption bands, readily accessible with existing upconverters. While our model shows that current bimolecular and lanthanide-based upconverting materials will improve cell efficiencies by <1%, cell efficiencies can increase by several absolute percent with increased upconverter quantum yield - even without an increased absorption bandwidth. By examining the efficiency limits of a highly realistic solar cell-upconverter system, our model provides a platform for optimizing future solar upconverter designs.

  1. Unraveling the effect of polymer dots doping in inverted low bandgap organic solar cells.

    Science.gov (United States)

    Zhang, Xinyuan; Liu, Chunyu; Li, Jinfeng; He, Yeyuan; Li, Zhiqi; Li, Hao; Shen, Liang; Guo, Wenbin; Ruan, Shengping

    2015-06-28

    In this study, molecular doping with polymer dots was designed to unravel its effect on the photoconductivity in organic solar cells. The photocurrent in organic solar cells exhibited a considerable increase under optimal doping concentration, leading to an ultimate enhancement of power conversion efficiency from 2.30% to 3.64%. This can be attributed primarily to the improvement of the initial boost in charge carriers due to the background carriers induced by the polymer dots and increased tail absorption by the active layer. Based on single carrier device and impedance measurements, polymer dopant can efficiently decrease charge recombination and improve charge carriers mobilities. The obtained achievements pave an approach of molecular doping in affecting the operation of organic solar cells.

  2. Incorporation of ester groups into low band-gap diketopyrrolopyrrole containing polymers for solar cell applications

    DEFF Research Database (Denmark)

    Hu, Xiaolian; Zuo, Lijian; Fu, Weifei

    2012-01-01

    To increase the open circuit voltage (VOC) of polymer solar cells based on diketopyrrolopyrrole (DPP) containing polymers, the weakly electron-withdrawing thiophene-3,4-dicarboxylate unit was introduced into the polymer backbone. Two ester group functionalized DPP containing polymers, PCTDPP...

  3. Fullerene derivative-doped zinc oxide nanofilm as the cathode of inverted polymer solar cells with low-bandgap polymer (PTB7-Th) for high performance.

    Science.gov (United States)

    Liao, Sih-Hao; Jhuo, Hong-Jyun; Cheng, Yu-Shan; Chen, Show-An

    2013-09-14

    Modification of a ZnO cathode by doping it with a hydroxyl-containing derivative - giving a ZnO-C60 cathode - provides a fullerene-derivative-rich surface and enhanced electron conduction. Inverted polymer solar cells with the ZnO-C60 cathode display markedly improved power conversion efficiency compared to those with a pristine ZnO cathode, especially when the active layer includes the low-bandgap polymer PTB7-Th.

  4. Single-Crystal Semiconductors with Narrow Band Gaps for Solar Water Splitting.

    Science.gov (United States)

    Wang, Tuo; Gong, Jinlong

    2015-09-07

    Solar water splitting provides a clean and renewable approach to produce hydrogen energy. In recent years, single-crystal semiconductors such as Si and InP with narrow band gaps have demonstrated excellent performance to drive the half reactions of water splitting through visible light due to their suitable band gaps and low bulk recombination. This Minireview describes recent research advances that successfully overcome the primary obstacles in using these semiconductors as photoelectrodes, including photocorrosion, sluggish reaction kinetics, low photovoltage, and unfavorable planar substrate surface. Surface modification strategies, such as surface protection, cocatalyst loading, surface energetics tuning, and surface texturization are highlighted as the solutions.

  5. Mapping Polymer Donors toward High-Efficiency Fullerene Free Organic Solar Cells.

    Science.gov (United States)

    Lin, Yuze; Zhao, Fuwen; Wu, Yang; Chen, Kai; Xia, Yuxin; Li, Guangwu; Prasad, Shyamal K K; Zhu, Jingshuai; Huo, Lijun; Bin, Haijun; Zhang, Zhi-Guo; Guo, Xia; Zhang, Maojie; Sun, Yanming; Gao, Feng; Wei, Zhixiang; Ma, Wei; Wang, Chunru; Hodgkiss, Justin; Bo, Zhishan; Inganäs, Olle; Li, Yongfang; Zhan, Xiaowei

    2017-01-01

    Five polymer donors with distinct chemical structures and different electronic properties are surveyed in a planar and narrow-bandgap fused-ring electron acceptor (IDIC)-based organic solar cells, which exhibit power conversion efficiencies of up to 11%.

  6. Performance enhancement of the P3HT/PCBM solar cells through NIR sensitization using a small-bandgap polymer

    Energy Technology Data Exchange (ETDEWEB)

    Ameri, Tayebeh; Min, Jie; Li, Ning; Machui, Florian; Baran, Derya [Institute Materials for Electronics and Energy Technology (I-MEET), Department of Materials Science and Engineering, Friedrich-Alexander University Erlangen-Nuremberg, Erlangen (Germany); Forster, Michael; Schottler, Kristina J.; Dolfen, Daniel; Scherf, Ullrich [FB C - Mathematik and Naturwissenschaften, Fachgebiet Makromolekulare Chemie and Institut fuer Polymertechnologie, Bergische Universitaet Wuppertal (Germany); Brabec, Christoph J. [Institute Materials for Electronics and Energy Technology (I-MEET), Department of Materials Science and Engineering, Friedrich-Alexander University Erlangen-Nuremberg, Erlangen (Germany); Bavarian Center for Applied Energy Research (ZAE Bayern), Erlangen (Germany)

    2012-10-15

    A smart strategy to significantly improve the energy conversion efficiency of the wide-bandgap polymer P3HT blended in PCBM is demonstrated through NIR sensitization with a low-bandgap polymer. An efficiency of over 4% is achieved by adding 30-40% of the low bandgap polymer Si-PCPDTBT to the binary P3HT:PCBM blend, corresponding to an efficiency improvement of 25% compared to the P3HT:PCBM reference binary blend. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  7. 100-Period InGaAsP/InGaP Superlattice Solar Cell with Sub-Bandgap Quantum Efficiency Approaching 80%

    Energy Technology Data Exchange (ETDEWEB)

    Steiner, Myles A [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Sayed, Islam [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Jain, Nikhil [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Geisz, John F [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Bedair, S. M. [North Carolina State University

    2017-08-25

    InGaAsP/InGaP quantum well (QW) structures are promising materials for next generation photovoltaic devices because of their tunable bandgap (1.50-1.80 eV) and being aluminum-free. However, the strain-balance limitations have previously limited light absorption in the QW region and constrained the external quantum efficiency (EQE) values beyond the In0.49Ga0.51P band-edge to less than 25%. In this work, we show that implementing a hundred period lattice matched InGaAsP/InGaP superlattice solar cell with more than 65% absorbing InGaAsP well resulted in more than 2x improvement in EQE values than previously reported strain balanced approaches. In addition, processing the devices with a rear optical reflector resulted in strong Fabry-Perot resonance oscillations and the EQE values were highly improved in the vicinity of these peaks, resulting in a short circuit current improvement of 10% relative to devices with a rear optical filter. These enhancements have resulted in an InGaAsP/InGaP superlattice solar cell with improved peak sub-bandgap EQE values exceeding 75% at 700 nm, an improvement in the short circuit current of 26% relative to standard InGaP devices, and an enhanced bandgap-voltage offset (Woc) of 0.4 V.

  8. Type-II InP quantum dots in wide-bandgap InGaP host for intermediate-band solar cells

    Science.gov (United States)

    Tayagaki, Takeshi; Sugaya, Takeyoshi

    2016-04-01

    We demonstrate type-II quantum dots (QDs) with long carrier lifetimes in a wide-bandgap host as a promising candidate for intermediate-band solar cells. Type-II InP QDs are fabricated in a wide-bandgap InGaP host using molecular beam epitaxy. Time-resolved photoluminescence measurements reveal an extremely long carrier lifetime (i.e., greater than 30 ns). In addition, from temperature-dependent PL spectra, we find that the type-II InP QDs form a negligible valence band offset and conduction band offset of ΔEc ≈ 0.35 eV in the InGaP host. Such a type-II confinement potential for InP/InGaP QDs has a significant advantage for realizing efficient two-step photon absorption and suppressed carrier capture in QDs via Auger relaxation.

  9. Efficient flexible inverted small-bandgap organic solar cells with low-temperature zinc oxide interlayer

    Science.gov (United States)

    You, Hailong; Zhang, Junchi; Zhang, Chunfu; Lin, Zhenhua; Chen, Dazheng; Chang, Jingjing; Zhang, Jincheng

    2016-12-01

    In this work, we employ an aqueous solution-processed ZnO layer on indium tin oxide (ITO)-coated poly(ethylene terephthalate) (PET) as an electron-selective layer in a flexible inverted organic solar cell (OSC) based on poly({4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b‧]dithiophene-2,6-diyl}{3-fluoro-2-[(2-ethylhexy)carbonyl]thieno[3,4-b]thiophenediyl}):[6,6]-phenyl-C71-butyric acid methyl ester (PTB-7:PC71BM) blends. The electron-selective ZnO layer is prepared in a low-temperature process so that it can be compatible with a flexible substrate. An efficient flexible OSC with the configuration PET/ITO/ZnO/PTB7:PC71BM/MoO3/Ag with a power conversion efficiency (PCE) above 7.6% is obtained. The flexible device could maintain 85% of its initial PCE after 240 h when exposed under air ambient condition without any encapsulation and with a humidity of around 40%. This flexible device shows superior mechanical properties and could keep 93% of its original efficiency after 1000 bending cycles with a curvature radius of 0.8 cm. The results show that the ZnO layer deposited as the electron-selective layer through the aqueous solution is suitable for flexible OSCs.

  10. Photo-electrochemical hydrogen generation using band-gap modified nanotubular titanium oxide in solar light

    Science.gov (United States)

    Raja, K. S.; Misra, M.; Mahajan, V. K.; Gandhi, T.; Pillai, P.; Mohapatra, S. K.

    Anodization of Ti in acidified fluoride solution results in an ordered nanotubular titanium oxide surface. In this study, vertically oriented arrays of TiO 2 nanotubes were prepared by incorporating nitrate and phosphate species during the anodization process. These nanotubes were annealed at 650 °C in a carbonaceous atmosphere using a chemical vapor deposition (CVD) furnace for a brief period. The carbon-modified nanotubular TiO 2 produced a photo-current density of more than 2.75 mA cm -2 at 0.2 V Ag/AgCl under solar light illumination. This photo-current density corresponds to a hydrogen evolution rate of about 11 l h -1 using a photo-anode of 1 m 2 area. The enhanced hydrogen evolution behavior of carbon-modified nanotubular TiO 2 is highly reproducible and sustainable for long duration. Annealed (at 350 °C in nitrogen atmosphere) TiO 2 nanotubes showed improved photo-activity as compared to the as-anodized or thermally oxidized TiO 2 photo-anodes.

  11. Ultra-Narrow Negative Flare Front Observed in Helium-10830 Å Using the1.6m New Solar Telescope

    Science.gov (United States)

    Xu, Yan; Cao, Wenda; Ding, Mingde; Kleint, Lucia; Su, Jiangtao; Liu, Chang; Ji, Haisheng; Chae, Jongchul; Jing, Ju; Cho, Kyuhyoun; Cho, Kyung-Suk; Gary, Dale E.; Wang, Haimin

    2016-05-01

    Solar flares are sudden flashes of brightness on the Sun and are often associated with coronal mass ejections and solar energetic particles that have adverse effects on the near-Earth environment. By definition, flares are usually referred to as bright features resulting from excess emission. Using the newly commissioned 1.6-m New Solar Telescope at Big Bear Solar Observatory, we show a striking “negative” flare with a narrow but unambiguous “dark” moving front observed in He I 10830 Å, which is as narrow as 340 km and is associated with distinct spectral characteristics in Hα and Mg II lines. Theoretically, such negative contrast in He I 10830 Å can be produced under special circumstances by nonthermal electron collisions or photoionization followed by recombination. Our discovery, made possible due to unprecedented spatial resolution, confirms the presence of the required plasma conditions and provides unique information in understanding the energy release and radiative transfer in solar flares.

  12. Theoretical optimization and parametric study of n-on-p Al/x/Ga/1-x/As-GaAs graded band-gap solar cell

    Science.gov (United States)

    Hutchby, J. A.; Fudurich, R. L.

    1976-01-01

    A comprehensive theoretical model of the graded band-gap Al(x)Ga(1-x)As-GaAs solar cell is used to optimize the n-on-p cell. The model includes power losses due to surface, bulk, and junction minority-carrier recombination, series resistance, and photon reflection from an SiO antireflection coating of optimum thickness. The optimized cell has a junction depth/graded band-gap layer thickness of 1.0 micron, respective donor and acceptor concentrations of 4 x 10 to the 17th power and 2 x 10 to the 17th power per cu cm, and a surface AlAs mode fraction of x = 0.35. The optimized graded band-gap cell has an air-mass-zero efficiency of 17.7% (not corrected for a 13% front surface contact area) and is shown to be less sensitive than a similar n-on-p GaAs cell to material degradation in the form of decreased minority-carrier diffusion lengths and increased surface-recombination velocity

  13. Fabry-P\\'erot based Narrow Band Imager for Solar Filament Observations

    CERN Document Server

    Dhara, Sajal Kumar; Banyal, Ravinder Kumar

    2015-01-01

    We have recently developed a narrow band imager (NBI) using an air gap based Fabry-P\\'erot (FP) interferometer at the Indian Institute of Astrophysics, Bangalore. Narrow band imaging is achieved by using an FP interferometer working in combination with an order sorting pre-filter. The NBI can be tuned to a different wavelength position on the line profile by changing the plate separation of the FP. The interferometer has a 50 mm clear aperture with a bandpass of $\\sim$247.8 m\\AA and a free spectral range of $\\sim$5.3\\AA at $\\lambda$ = 656.3 nm. The developed NBI is used to observe the solar filament in the H$\\alpha$ wavelength. The instrument is being used to image the Sun at chromospheric height and it is also able to scan the H$\\alpha$ spectral line profile at different wavelength positions. We have also made Doppler velocity maps at chromospheric height by taking the blue and red wing images at $\\pm$176 m\\AA wavelength positions separately away from the line center of the spectral line. In this paper, we p...

  14. Double-graded bandgap in Cu(In,Ga)Se2 thin film solar cells by low toxicity selenization process

    Science.gov (United States)

    Wang, Yi-Chih; Shieh, Han-Ping D.

    2014-08-01

    A low-toxic selenization with post gallium diffusion (PGD) treatment has been demonstrated to increase the bandgap in the surface Cu(In,Ga)Se2 (CIGSe) absorbers and to form double-graded bandgap profiles to improve the cell efficiency. The CIGSe absorber with PGD for 5 min increased open-circuit voltage from 0.49 to 0.66 V and efficiency from 9.2% to 13.2%, contributed by the enhancement of carrier recombination in the space-charge region. The reduction in short-circuit current from 30.8 to 29.9 mA/cm2, attributed to the absorption loss in long-wavelength regions, can be potentially improved by further optimization of the minimum bandgap value in gradient valley.

  15. New insights into the band-gap narrowing of (N, P)-codoped TiO2 from hybrid density functional theory calculations.

    Science.gov (United States)

    Long, Run; English, Niall J

    2011-10-04

    The electronic properties of anatase-TiO(2) codoped by N and P at different concentrations have been investigated via generalized Kohn-Sham theory with the Heyd-Scuseria-Ernzerhof (HSE06) hybrid functional for exchange-correlation in the context of density functional theory. At high doping concentrations, we find that the high photocatalytic activity of (N, P)-codoped anatase TiO(2) vis-à-vis the N-monodoped case can be rationalized by a double-hole-mediated coupling mechanism [Yin et al., Phys. Rev. Lett. 2011, 106, 066801] via the formation of an effective N-P bond. On the other hand, Ti(3+) and Ti(4+) ions' spin double-exchange results in more substantial gap narrowing for larger separations between N and P atoms. At low doping concentrations, double-hole-coupling is dominant, regardless of the N-P distance. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. Ultra-narrow Negative Flare Front Observed in Helium-10830~\\AA\\ using the 1.6 m New Solar Telescope

    CERN Document Server

    Xu, Yan; Ding, Mingde; Kleint, Lucia; Su, Jiangtao; Liu, Chang; Ji, Haisheng; Chae, Jongchul; Jing, Ju; Cho, Kyuhyoun; Cho, Kyungsuk; Gary, Dale; Wang, Haimin

    2016-01-01

    Solar flares are sudden flashes of brightness on the Sun and are often associated with coronal mass ejections and solar energetic particles which have adverse effects in the near Earth environment. By definition, flares are usually referred to bright features resulting from excess emission. Using the newly commissioned 1.6~m New Solar Telescope at Big Bear Solar Observatory, here we show a striking "negative" flare with a narrow, but unambiguous "dark" moving front observed in He I 10830 \\AA, which is as narrow as 340 km and is associated with distinct spectral characteristics in H-alpha and Mg II lines. Theoretically, such negative contrast in He I 10830 \\AA\\ can be produced under special circumstances, by nonthermal-electron collisions, or photoionization followed by recombination. Our discovery, made possible due to unprecedented spatial resolution, confirms the presence of the required plasma conditions and provides unique information in understanding the energy release and radiative transfer in astronomi...

  17. Spectral data of specular reflectance, narrow-angle transmittance and angle-resolved surface scattering of materials for solar concentrators.

    Science.gov (United States)

    Good, Philipp; Cooper, Thomas; Querci, Marco; Wiik, Nicolay; Ambrosetti, Gianluca; Steinfeld, Aldo

    2016-03-01

    The spectral specular reflectance of conventional and novel reflective materials for solar concentrators is measured with an acceptance angle of 17.5 mrad over the wavelength range 300-2500 nm at incidence angles 15-60° using a spectroscopic goniometry system. The same experimental setup is used to determine the spectral narrow-angle transmittance of semi-transparent materials for solar collector covers at incidence angles 0-60°. In addition, the angle-resolved surface scattering of reflective materials is recorded by an area-scan CCD detector over the spectral range 350-1050 nm. A comprehensive summary, discussion, and interpretation of the results are included in the associated research article "Spectral reflectance, transmittance, and angular scattering of materials for solar concentrators" in Solar Energy Materials and Solar Cells.

  18. Spectral data of specular reflectance, narrow-angle transmittance and angle-resolved surface scattering of materials for solar concentrators

    Directory of Open Access Journals (Sweden)

    Philipp Good

    2016-03-01

    Full Text Available The spectral specular reflectance of conventional and novel reflective materials for solar concentrators is measured with an acceptance angle of 17.5 mrad over the wavelength range 300−2500 nm at incidence angles 15–60° using a spectroscopic goniometry system. The same experimental setup is used to determine the spectral narrow-angle transmittance of semi-transparent materials for solar collector covers at incidence angles 0–60°. In addition, the angle-resolved surface scattering of reflective materials is recorded by an area-scan CCD detector over the spectral range 350–1050 nm. A comprehensive summary, discussion, and interpretation of the results are included in the associated research article “Spectral reflectance, transmittance, and angular scattering of materials for solar concentrators” in Solar Energy Materials and Solar Cells.

  19. Low-bandgap poly(thiophene-phenylene-thiophene) derivatives with broaden absorption spectra for use in high-performance bulk-heterojunction polymer solar cells.

    Science.gov (United States)

    Chen, Chih-Ping; Chan, Shu-Hua; Chao, Teng-Chih; Ting, Ching; Ko, Bao-Tsan

    2008-09-24

    Two low-bandgap (LGB) conjugated polymers ( P1 and P2) based on thiophene-phenylene-thiophene (TPT) with adequate energy levels have been designed and synthesized for application in bulk-heterojunction polymer solar cells (PSCs). The absorption spectral, electrochemical, field effect hole mobility and photovoltaic properties of LGB TPT derivatives are investigated and compared with poly(3-hexylthiophene) (P3HT). Photophysical studies reveal bandgaps of 1.76 eV for P1 and 1.70 eV for P2, which could effectively harvest broader solar spectrum. In addition, the thin film absorption coefficients of P1 and P2 are 1.6 x 10 (5) cm (-1) (lambda approximately 520 nm) and 1.4 x 10 (5) cm (-1) (lambda approximately 590 nm), respectively. Electrochemical studies indicate desirable HOMO/LUMO levels that enable a high open circuit voltage while blending them with fullerene derivatives as electron acceptors. Furthermore, both materials show sufficient hole mobility (3.4 x 10 (-3) cm (2)/Vs for P2) allowing efficient charge extraction and a good fill-factor for PSC application. High-performance power conversion efficiency (PCE) of 4.4% is obtained under simulated solar light AM 1.5 G (100 mW/cm (2)) from PSC device with an active layer containing 25 wt% P2 and 75 wt% [6,6]-phenyl-C71-butyric acid methyl ester (PC 71BM), which is superior to that of the analogous P3HT cell (3.9%) under the same experimental condition.

  20. Highly efficient and thickness-tolerable bulk heterojunction polymer solar cells based on P3HT donor and a low-bandgap non-fullerene acceptor

    Science.gov (United States)

    Liu, Xiaodong; Li, Yongxi; Huang, Peng; Zhou, Yi; Jiang, Zuo-Quan; Song, Bo; Li, Yongfang; Liao, Liang-Sheng; Zheng, Yonghao

    2017-10-01

    In order to fabricate highly efficient polymer solar cells (PSCs) in industrial scale, one of the key issues is to use thick active layer (>200 nm) in the device module without sacrificing the power conversion efficiency (PCE). In this article, we have studied the blend of the medium-bandgap polymeric donor P3HT and the low-bandgap acceptor IDTIDT-IC as the active layer in non-fullerene PSCs, and successfully maintained the device performance with the thickness of the active layer close to 250 nm. The P3HT:IDTIDT-IC based PSCs with simple thermal annealing exhibits a PCE of 3.49% at a thin active layer, 74 nm. More importantly, the PCE remains almost constant with increasing the thickness of the active layer, and reaches a peak value of 3.64% at 236 nm. This thickness-insensitive photovoltaic performance of the P3HT:IDTIDT-IC system makes them compatible with large-scale roll-to-roll processing. Furthermore, the P3HT:IDTIDT-IC devices show a very high tolerance to temperature, and the PCE keeps nearly unchanged after annealing the active layer at 150 °C for 75 min. All in all, our results show that thickness-tolerable and thermal-stable P3HT:IDTIDT-IC system is more suitable for large-scale industrial manufacturing than the classic P3HT:PCBM formula.

  1. Wide Bandgap Nanostructured Space Photovoltaics Project

    Data.gov (United States)

    National Aeronautics and Space Administration — Firefly, in collaboration with Rochester Institute of Technology, proposes an STTR program for the development of a wide-bandgap GaP-based space solar cell capable...

  2. Wide Band-Gap 3,4-Difluorothiophene-Based Polymer with 7% Solar Cell Efficiency: an Alternative to P3HT

    KAUST Repository

    Wolf, Jannic Sebastian

    2015-05-27

    We report on a wide band-gap polymer donor composed of benzo[1,2-b:4,5-b\\']dithiophene (BDT) and 3,4-difluorothiophene ([2F]T) units (Eopt ~2.1 eV), and show that the fluorinated analog PBDT[2F]T performs significantly better than its non-fluorinated counterpart PBDT[2H]T in BHJ solar cells with PC71BM. While control P3HT- and PBDT[2H]T-based devices yield PCEs of ca. 4% and 3% (Max.) respectively, PBDT[2F]T-based devices reach PCEs of ca. 7%, combining a large Voc of ca. 0.9 V and short-circuit current values (ca. 10.7 mA/cm2) comparable to those of the best P3HT-based control devices.

  3. Modeling and simulation of band-gap profiling with planar heterojunction of hole-transporting layer-free perovskite solar cells

    Science.gov (United States)

    Liu, Yung-Tsung; Chen, Yu-Hung; Lin, Chen-Cheng; Fan, Chia-Ming; Liu, Jun-Chin; Tung, Yung-Liang; Tsai, Song-Yeu

    2017-07-01

    This study entailed modeling a perovskite absorber involving band-gap grading at the back of the absorber and double-grading profiles of hole-transporting layer-free perovskite solar cells. Device simulation based on continuity equations and Poisson’s equation was carried out by using AMPS-1D software. The optimum grading profile consisted of a band gap of 1.7 eV at the interface between the TiO2 and absorber with a graded thickness of 300 nm, uniform 1.5 eV of 50 nm, and back surface 2.1 eV with a graded thickness of 50 nm. The attained simulated efficiency was 22.68% (open-circuit voltage, V oc  =  1.34 V; short-circuit current density, J sc  =  19.98 mA cm-2 fill factor, FF  =  0.84), which is close to the uniform band gap of 1.5 eV of the whole absorber with a hole-transporting layer (Spiro-OMeTAD). This was mainly because of back grading forming a conduction band energy barrier to suppress the transportation of photo-generated electrons from the absorber to the back electrode, thereby improving carrier collection. The results indicate that the hole-transporting layer could be replaced by optimal band-gap profiling of the absorber, with near to no decayed performance of the perovskite solar cells.

  4. Ga-rich GaxIn1-xP solar cells on Si with 1.95 eV bandgap for ideal III-V/Si photovoltaics

    Science.gov (United States)

    Ratcliff, Christopher; Grassman, T. J.; Carlin, J. A.; Chmielewski, D. J.; Ringel, S. A.

    2014-03-01

    Theoretical models for III-V compound multijunction solar cells show that solar cells with bandgaps of 1.95-2.3 eV are needed to create ideal optical partitioning of the solar spectrum for device architectures containing three, four and more junctions. For III-V solar cells integrated with an active Si sub-cell, GaInP alloys in the Ga-rich regime are ideal since direct bandgaps of up to ~ 2.25 eV are achieved at lattice constants that can be integrated with appropriate GaAsP, SiGe and Si materials, with efficiencies of almost 50% being predicted using practical solar cell models under concentrated sunlight. Here we report on Ga-rich, lattice-mismatched Ga0.57In0.43P sub-cell prototypes with a bandgap of 1.95 eV grown on tensile step-graded metamorphic GaAsyP1-y buffers on GaAs substrates. The goal is to create a high bandgap top cell for integration with Si-based III-V/Si triple-junction devices. Excellent carrier collection efficiency was measured via internal quantum efficiency measurements and with their design being targeted for multijunction implementation (i.e. they are too thin for single junction cells), initial cell results are encouraging. The first generation of identical 1.95 eV cells on Si were fabricated as well, with efficiencies for these large bandgap, thin single junction cells ranging from 7% on Si to 11% on GaAs without antireflection coatings, systematically tracking the change in defect density as a function of growth substrate.

  5. ULTRA-NARROW NEGATIVE FLARE FRONT OBSERVED IN HELIUM-10830 Å USING THE 1.6 m NEW SOLAR TELESCOPE

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Yan; Liu, Chang; Jing, Ju; Wang, Haimin [Space Weather Research Lab, Center for Solar-Terrestrial Research, New Jersey Institute of Technology, 323 Martin Luther King Blvd, Newark, NJ 07102-1982 (United States); Cao, Wenda; Gary, Dale [Big Bear Solar Observatory, New Jersey Institute of Technology 323 Martin Luther King Blvd, Newark, NJ 07102-1982 (United States); Ding, Mingde [School of Astronomy and Space Science, Nanjing University, Nanjing 210093 (China); Kleint, Lucia [Fachhochschule Nordwestschweiz (FHNW), Institute of 4D technologies Bahnhofstr. 6, CH-5210 Windisch (Switzerland); Su, Jiangtao [Key Laboratory of Solar Activity, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 (China); Ji, Haisheng [Purple Mountain Observatory, 2 Beijing Xi Lu, Nanjing, 210008 (China); Chae, Jongchul; Cho, Kyuhyoun [Astronomy Program, Department of Physics and Astronomy, Seoul National University, Seoul 151-747 (Korea, Republic of); Cho, Kyungsuk [Korea Astronomy and Space Science Institute, Daedeokdae-ro 776, Yuseong-gu, Daejeon 305-348 (Korea, Republic of)

    2016-03-10

    Solar flares are sudden flashes of brightness on the Sun and are often associated with coronal mass ejections and solar energetic particles that have adverse effects on the near-Earth environment. By definition, flares are usually referred to as bright features resulting from excess emission. Using the newly commissioned 1.6 m New Solar Telescope at Big Bear Solar Observatory, we show a striking “negative” flare with a narrow but unambiguous “dark” moving front observed in He i 10830 Å, which is as narrow as 340 km and is associated with distinct spectral characteristics in Hα and Mg ii lines. Theoretically, such negative contrast in He i 10830 Å can be produced under special circumstances by nonthermal electron collisions or photoionization followed by recombination. Our discovery, made possible due to unprecedented spatial resolution, confirms the presence of the required plasma conditions and provides unique information in understanding the energy release and radiative transfer in astronomical objects.

  6. Ultra-wide bandgap beta-Ga2O3 for deep-UV solar blind photodetectors(Conference Presentation)

    Science.gov (United States)

    Rafique, Subrina; Han, Lu; Zhao, Hongping

    2017-03-01

    Deep-ultraviolet (DUV) photodetectors based on wide bandgap (WB) semiconductor materials have attracted strong interest because of their broad applications in military surveillance, fire detection and ozone hole monitoring. Monoclinic β-Ga2O3 with ultra-wide bandgap of 4.9 eV is a promising candidate for such application because of its high optical transparency in UV and visible wavelength region, and excellent thermal and chemical stability at elevated temperatures. Synthesis of high qualityβ-Ga2O3 thin films is still at its early stage and knowledge on the origins of defects in this material is lacking. The conventional epitaxy methods used to grow β-Ga2O3 thin films such as molecular beam epitaxy (MBE) and metal organic chemical vapor deposition (MOCVD) still face great challenges such as limited growth rate and relatively high defects levels. In this work, we present the growth of β-Ga2O3 thin films on c-plane (0001) sapphire substrate by our recently developed low pressure chemical vapor deposition (LPCVD) method. The β-Ga2O3 thin films synthesized using high purity metallic gallium and oxygen as the source precursors and argon as carrier gas show controllable N-type doping and high carrier mobility. Metal-semiconductor-metal (MSM) photodetectors (PDs) were fabricated on the as-grown β-Ga2O3 thin films. Au/Ti thin films deposited by e-beam evaporation served as the contact metals. Optimization of the thin film growth conditions and the effects of thermal annealing on the performance of the PDs were investigated. The responsivity of devices under 250 nm UV light irradiation as well as dark light will be characterized and compared.

  7. Hydrophilic Conjugated Polymers with Large Bandgaps and Deep-Lying HOMO Levels as an Efficient Cathode Interlayer in Inverted Polymer Solar Cells.

    Science.gov (United States)

    Kan, Yuanyuan; Zhu, Yongxiang; Liu, Zhulin; Zhang, Lianjie; Chen, Junwu; Cao, Yong

    2015-08-01

    Two hydrophilic conjugated polymers, PmP-NOH and PmP36F-NOH, with polar diethanol-amine on the side chains and main chain structures of poly(meta-phenylene) and poly(meta-phenylene-alt-3,6-fluorene), respectively, are successfully synthesized. The films of PmP-NOH and PmP36F-NOH show absorption edges at 340 and 343 nm, respectively. The calculated optical bandgaps of the two polymers are 3.65 and 3.62 eV, respectively, the largest ones so far reported for hydrophilic conjugated polymers. PmP-NOH and PmP36F-NOH also possess deep-lying highest occupied molecular orbital levels of -6.19 and -6.15 eV, respectively. Inserting PmP-NOH and PmP36F-NOH as a cathode interlayer in inverted polymer solar cells with a PTB7/PC71 BM blend as the active layer, high power conversion efficiencies of 8.58% and 8.33%, respectively, are achieved, demonstrating that the two hydrophilic polymers are excellent interlayers for efficient inverted polymer solar cells.

  8. Au@Ag core-shell nanocubes for efficient plasmonic light scattering effect in low bandgap organic solar cells.

    Science.gov (United States)

    Baek, Se-Woong; Park, Garam; Noh, Jonghyeon; Cho, Changsoon; Lee, Chun-Ho; Seo, Min-Kyo; Song, Hyunjoon; Lee, Jung-Yong

    2014-04-22

    In this report, we propose a metal-metal core-shell nanocube (NC) as an advanced plasmonic material for highly efficient organic solar cells (OSCs). We covered an Au core with a thin Ag shell as a scattering enhancer to build Au@Ag NCs, which showed stronger scattering efficiency than Au nanoparticles (AuNPs) throughout the visible range. Highly efficient plasmonic organic solar cells were fabricated by embedding Au@Ag NCs into an anodic buffer layer, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), and the power conversion efficiency was enhanced to 6.3% from 5.3% in poly[N-9-hepta-decanyl-2,7-carbazole-alt-5,5-(4,7-di-2-thienyl-2,1,3-benzothiadiazole)] (PCDTBT):[6,6]-phenyl C71-butyric acid methyl ester (PC70BM) based OSCs and 9.2% from 7.9% in polythieno[3,4-b]thiophene/benzodithiophene (PTB7):PC70BM based OSCs. The Au@Ag NC plasmonic PCDTBT:PC70BM-based organic solar cells showed 2.2-fold higher external quantum efficiency enhancement compared to AuNPs devices at a wavelength of 450-700 nm due to the amplified plasmonic scattering effect. Finally, we proved the strongly enhanced plasmonic scattering efficiency of Au@Ag NCs embedded in organic solar cells via theoretical calculations and detailed optical measurements.

  9. Conduction band offset engineering in wide-bandgap Ag(In,Ga)Se2 solar cells by hybrid buffer layer

    Science.gov (United States)

    Umehara, Takeshi; Zulkifly, Faris Akira Bin Mohd; Nakada, Kazuyoshi; Yamada, Akira

    2017-08-01

    Ag(In,Ga)Se2 (AIGS) is one of the promising candidates for the top cell absorber in the tandem structure. However, the conversion efficiency of AIGS solar cells is still lower than that required for the top cell. In this study, to improve the conversion efficiency of AIGS solar cells, we controlled the conduction band offset (CBO) at the buffer layer/ZnO and buffer layer/AIGS interfaces. The reduction in interface recombination at the CdS buffer layer/AIGS interface was achieved by introducing a ZnS(O,OH) buffer layer instead of a CdS buffer layer, although the fill factor (FF) decreased markedly because the CBO at the ZnS(O,OH)/ZnO interface prevented the electron flow under a forward bias. We found that the introduction of a CdS/ZnS(O,OH) hybrid buffer layer is efficient in controlling the CBO at both the buffer layer/AIGS and buffer layer/ZnO interfaces and improving the solar cell conversion efficiency.

  10. Studies of silicon p-n junction solar cells

    Science.gov (United States)

    Neugroschel, A.; Lindholm, F. A.

    1979-01-01

    To provide theoretical support for investigating different ways to obtain high open-circuit voltages in p-n junction silicon solar cells, an analytical treatment of heavily doped transparent-emitter devices is presented that includes the effects of bandgap narrowing, Fermi-Dirac statistics, a doping concentration gradient, and a finite surface recombination velocity at the emitter surface. Topics covered include: (1) experimental determination of bandgap narrowing in the emitter of silicon p-n junction devices; (2) heavily doped transparent regions in junction solar cells, diodes, and transistors; (3) high-low-emitter solar cell; (4) determination of lifetimes and recombination currents in p-n junction solar cells; (5) MOS and oxide-charged-induced BSF solar cells; and (6) design of high efficiency solar cells for space and terrestrial applications.

  11. Catalyzed Water Oxidation by Solar Irradiation of Band-Gap-Narrowed Semiconductors (Part 1. Overview).

    Energy Technology Data Exchange (ETDEWEB)

    Fujita,E.; Khalifah, P.; Lymar, S.; Muckerman, J.T.; Rodgriguez, J.

    2008-03-18

    The objectives of this report are: (1) Investigate the catalysis of water oxidation by cobalt and manganese hydrous oxides immobilized on titania or silica nanoparticles, and dinuclear metal complexes with quinonoid ligands in order to develop a better understanding of the critical water oxidation chemistry, and rationally search for improved catalysts. (2) Optimize the light-harvesting and charge-separation abilities of stable semiconductors including both a focused effort to improve the best existing materials by investigating their structural and electronic properties using a full suite of characterization tools, and a parallel effort to discover and characterize new materials. (3) Combine these elements to examine the function of oxidation catalysts on Band-Gap-Narrowed Semiconductor (BGNSC) surfaces and elucidate the core scientific challenges to the efficient coupling of the materials functions.

  12. Photonic bandgap fiber bundle spectrometer

    CERN Document Server

    Hang, Qu; Syed, Imran; Guo, Ning; Skorobogatiy, Maksim

    2010-01-01

    We experimentally demonstrate an all-fiber spectrometer consisting of a photonic bandgap fiber bundle and a black and white CCD camera. Photonic crystal fibers used in this work are the large solid core all-plastic Bragg fibers designed for operation in the visible spectral range and featuring bandgaps of 60nm - 180nm-wide. 100 Bragg fibers were chosen to have complimentary and partially overlapping bandgaps covering a 400nm-840nm spectral range. The fiber bundle used in our work is equivalent in its function to a set of 100 optical filters densely packed in the area of ~1cm2. Black and white CCD camera is then used to capture spectrally "binned" image of the incoming light at the output facet of a fiber bundle. To reconstruct the test spectrum from a single CCD image we developed an algorithm based on pseudo-inversion of the spectrometer transmission matrix. We then study resolution limit of this spectroscopic system by testing its performance using spectrally narrow test peaks (FWHM 5nm-25nm) centered at va...

  13. High-Performance Polymer Solar Cells Based on a Wide-Bandgap Polymer Containing Pyrrolo[3,4-f]benzotriazole-5,7-dione with a Power Conversion Efficiency of 8.63.

    Science.gov (United States)

    Lan, Liuyuan; Chen, Zhiming; Hu, Qin; Ying, Lei; Zhu, Rui; Liu, Feng; Russell, Thomas P; Huang, Fei; Cao, Yong

    2016-09-01

    A novel donor-acceptor type conjugated polymer based on a building block of 4,8-di(thien-2-yl)-6-octyl-2-octyl-5H-pyrrolo[3,4-f]benzotriazole-5,7(6H)-dione (TZBI) as the acceptor unit and 4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)-benzo-[1,2-b:4,5-b']dithiophene as the donor unit, named as PTZBIBDT, is developed and used as an electron-donating material in bulk-heterojunction polymer solar cells. The resulting copolymer exhibits a wide bandgap of 1.81 eV along with relatively deep highest occupied molecular orbital energy level of -5.34 eV. Based on the optimized processing conditions, including thermal annealing, and the use of a water/alcohol cathode interlayer, the single-junction polymer solar cell based on PTZBIBDT:PC71BM ([6,6]-phenyl-C71-butyric acid methyl ester) blend film affords a power conversion efficiency of 8.63% with an open-circuit voltage of 0.87 V, a short circuit current of 13.50 mA cm(-2), and a fill factor of 73.95%, which is among the highest values reported for wide-bandgap polymers-based single-junction organic solar cells. The morphology studies on the PTZBIBDT:PC71BM blend film indicate that a fibrillar network can be formed and the extent of phase separation can be mani-pulated by thermal annealing. These results indicate that the TZBI unit is a very promising building block for the synthesis of wide-bandgap polymers for high-performance single-junction and tandem (or multijunction) organic solar cells.

  14. Bandgap engineering of Cu2CdxZn1−xSnS4 alloy for photovoltaic applications: A complementary experimental and first-principles study

    KAUST Repository

    Xiao, Zhen-Yu

    2013-11-11

    We report on bandgap engineering of an emerging photovoltaic material of Cu2CdxZn1-xSnS4 (CCZTS) alloy. CCZTS alloy thin films with different Cd contents and single kesterite phase were fabricated using the sol-gel method. The optical absorption measurements indicate that the bandgap of the kesterite CCZTS alloy can be continuously tuned in a range of 1.55-1.09 eV as Cd content varied from x = 0 to 1. Hall effect measurements suggest that the hole concentration of CCZTS films decreases with increasing Cd content. The CCZTS-based solar cell with x = 0.47 demonstrates a power conversion efficiency of 1.2%. Our first-principles calculations based on the hybrid functional method demonstrate that the bandgap of the kesterite CCZTS alloy decreases monotonically with increasing Cd content, supporting the experimental results. Furthermore, Cu2ZnSnS4/Cu 2CdSnS4 interface has a type-I band-alignment with a small valence-band offset, explaining the narrowing of the bandgap of CCZTS as the Cd content increases. Our results suggest that CCZTS alloy is a potentially suitable material to fabricate high-efficiency multi-junction tandem solar cells with different bandgap-tailored absorption layers. © 2013 AIP Publishing LLC.

  15. High-efficiency, monolithic, multi-bandgap, tandem photovoltaic energy converters

    Science.gov (United States)

    Wanlass, Mark W.

    2011-11-29

    A monolithic, multi-bandgap, tandem solar photovoltaic converter has at least one, and preferably at least two, subcells grown lattice-matched on a substrate with a bandgap in medium to high energy portions of the solar spectrum and at least one subcell grown lattice-mismatched to the substrate with a bandgap in the low energy portion of the solar spectrum, for example, about 1 eV.

  16. Experimental investigation of the excess charge and time constant of minority carriers in the thin diffused layer of 0.1 Ohm-cm silicon solar cells

    Science.gov (United States)

    Godlewski, M. P.; Brandhorst, H. W., Jr.; Lindholm, F. A.; Sah, C. T.

    1976-01-01

    The observed low open-circuit voltage in 0.1 Ohm-cm solar cells is probably related to an excessively high diode saturation current. Theoretical studies conducted by Lindholm et al. (1975) and by Godlewski et al. (1975) have shown that a high saturation current could be produced by either high recombination rates or bandgap narrowing effects. A description is given of an investigation which shows that bandgap narrowing effects have a first order significance in determining the charge carrier transport controlling the open-circuit voltage of 0.1 Ohm-cm silicon solar cells.

  17. Experimental investigation of the excess charge and time constant of minority carriers in the thin diffused layer of 0.1 Ohm-cm silicon solar cells

    Science.gov (United States)

    Godlewski, M. P.; Brandhorst, H. W., Jr.; Lindholm, F. A.; Sah, C. T.

    1976-01-01

    The observed low open-circuit voltage in 0.1 Ohm-cm solar cells is probably related to an excessively high diode saturation current. Theoretical studies conducted by Lindholm et al. (1975) and by Godlewski et al. (1975) have shown that a high saturation current could be produced by either high recombination rates or bandgap narrowing effects. A description is given of an investigation which shows that bandgap narrowing effects have a first order significance in determining the charge carrier transport controlling the open-circuit voltage of 0.1 Ohm-cm silicon solar cells.

  18. Photonic Bandgap Fibers

    DEFF Research Database (Denmark)

    Barkou, Stig Eigil; Broeng, Jes; Bjarklev, Anders Overgaard

    1999-01-01

    Photonic bandgap fibers are describes using a new Kagomé cladding structure. These fibers may potentially guide light in low-index regions. Such fibers offer new dispersion properties, and large design flexibility.......Photonic bandgap fibers are describes using a new Kagomé cladding structure. These fibers may potentially guide light in low-index regions. Such fibers offer new dispersion properties, and large design flexibility....

  19. Hybrid nanocone forests with high absorption in full-solar spectrum for solar cell applications

    Science.gov (United States)

    Yang, Yudong; Mao, Haiyang; Xiong, Jijun; Ming, Anjie; Wang, Weibing

    2016-11-01

    In this work, hybrid nanocone forests (HNFs) with high absorption in full-solar-spectrum are fabricated based on a plasma repolymerization technique. The HNFs combine light trapping effect of the nanocone forests with surface plasmon resonance effect of the metallic nanoparticles, thus can achieve an optimized absorption larger than 80% in the full-solar spectrum (i.e. 200-2500nm). Besides, with the hybrid nanostructures, the absorption decrease around the Si bandgap width can be narrowed greatly, while the normalized utilization efficiency of solar radiation can be increased. Therefore, usage of the HNFs as a texture structure in solar cells to obtain higher conversion efficiencies is foreseeable.

  20. Low bandgap semiconducting polymers for polymeric photovoltaics.

    Science.gov (United States)

    Liu, Chang; Wang, Kai; Gong, Xiong; Heeger, Alan J

    2016-08-22

    In order to develop high performance polymer solar cells (PSCs), full exploitation of the sun-irradiation from ultraviolet (UV) to near infrared (NIR) is one of the key factors to ensure high photocurrents and thus high efficiency. In this review, five of the effective design rules for approaching LBG semiconducting polymers with high molar absorptivity, suitable energy levels, high charge carrier mobility and high solubility in organic solvents are overviewed. These design stratagems include fused heterocycles for facilitating π-electron flowing along the polymer backbone, groups/atoms bridging adjacent rings for maintaining a high planarity, introduction of electron-withdrawing units for lowering the bandgap (Eg), donor-acceptor (D-A) copolymerization for narrowing Eg and 2-dimensional conjugation for broadened absorption and enhanced hole mobility. It has been demonstrated that LBG semiconducting polymers based on electron-donor units combined with strong electron-withdrawing units possess excellent electronic and optic properties, emerging as excellent candidates for efficient PSCs. While for ultrasensitive photodetectors (PDs), which have intensive applications in both scientific and industrial sectors, sensing from the UV to the NIR region is of critical importance. For polymer PDs, Eg as low as 0.8 eV has been obtained through a rational design stratagem, covering a broad wavelength range from the UV to the NIR region (1450 nm). However, the response time of the polymer PDs are severely limited by the hole mobility of LBG semiconducting polymers, which is significantly lower than those of the inorganic materials. Thus, further advancing the hole mobility of LBG semiconducting polymers is of equal importance as broadening the spectral response for approaching uncooled ultrasensitive broadband polymer PDs in the future study.

  1. InGaP Heterojunction Barrier Solar Cells

    Science.gov (United States)

    Welser, Roger E. (Inventor)

    2014-01-01

    A new solar cell structure called a heterojunction barrier solar cell is described. As with previously reported quantum-well and quantum-dot solar cell structures, a layer of narrow band-gap material, such as GaAs or indium-rich InGaP, is inserted into the depletion region of a wide band-gap PN junction. Rather than being thin, however, the layer of narrow band-gap material is about 400-430 nm wide and forms a single, ultrawide well in the depletion region. Thin (e.g., 20-50 nm), wide band-gap InGaP barrier layers in the depletion region reduce the diode dark current. Engineering the electric field and barrier profile of the absorber layer, barrier layer, and p-type layer of the PN junction maximizes photogenerated carrier escape. This new twist on nanostructured solar cell design allows the separate optimization of current and voltage to maximize conversion efficiency.

  2. High-performance laterally-arranged multiple-bandgap solar cells using spatially composition-graded CdxPb1-xS nanowires on a single substrate: a design study.

    Science.gov (United States)

    Caselli, D A; Ning, C Z

    2011-07-04

    In this paper, laterally arranged multiple bandgap (LAMB) solar cells based on CdxPb1-xS alloy nanowires of varying composition on a single substrate are designed to be used together with a dispersive concentrator. Simulation results for a design with six subcells in series connection are presented. The design is based on a unique materials capability achieved in our recent research. An efficiency of 34.9% was obtained for operation without solar concentration, which increased to 40.5%, 41.7%, and 42.7% for concentration ratios of 25, 100, and 240 respectively. The device was also simulated with decreased carrier mobilities to model the possible reduction in absorber conductivity, depending on the nanowire geometry and configuration. For a concentration ratio of unity, decreasing the mobilities to 25% of their original values caused less than a 2.5% absolute drop in efficiency. The LAMB design offers the advantages of an integrated cell platform and the potential for low-cost, high efficiency photovoltaic systems.

  3. Polymer Solar Cells: High‐Performance Polymer Solar Cells Based on a Wide‐Bandgap Polymer Containing Pyrrolo[3,4‐f]benzotriazole‐5,7‐dione with a Power Conversion Efficiency of 8.63% (Adv. Sci. 9/2016)

    OpenAIRE

    Lan, Liuyuan; Chen, Zhiming; Hu, Qin; Ying, Lei; Zhu, Rui; Liu, Feng(Central China Normal University, Wuhan, 430079, People's Republic of China); Russell, Thomas P.; Huang, Fei; Cao, Yong

    2016-01-01

    In article 1600032, an efficient new wide‐bandgap polymer based on a novel moiety of pyrrolo[3,4‐f]benzotriazole‐5,7‐dione (TZBI) is developed by Lei Ying, Feng Lui, Thomas P. Russel, Fei Huang, and co‐workers. The new chemistry enables fine electronic structure tuning and solution‐processed single‐junction polymer solar cells provided a remarkable power conversion efficiency of 8.63%. Full electrical and structural characterization reveales that TZBI is a promising building block for the app...

  4. Recent ROB developments on wide bandgap based UV sensors

    Science.gov (United States)

    Giordanengo, B.; Ben Moussa, A.; Hochedez, J.-F.; Soltani, A.; de Moor, P.; Minoglou, K.; Malinowski, P.; Duboz, J.-Y.; Chong, Y. M.; Zou, Y. S.; Zhang, W. J.; Lee, S. T.; Dahal, R.; Li, J.; Lin, J. Y.; Jiang, H. X.

    The next ESA spatial mission planned to study the Sun, Solar Orbiter (SO), necessitates very innovative EUV detectors. The commonly used silicon detectors suffer important limitations mainly in terms of UV robustness and dark current level. An alternative comes from diamond or III-nitride materials. In these materials, the radiation hardness, solar blindness and dark current are improved due to their wide bandgap. This paper presents the new developments on wide bandgap materials at the Royal Observatory of Belgium (ROB). We present also the LYRA instrument, the BOLD project, and the EUI instrument suite.

  5. Organic-Inorganic Hybrid Ternary Bulk Heterojunction of Nanostructured Perovskite-Low Bandgap Polymer-PCBM for Improved Efficiency of Organic Solar Cells.

    Science.gov (United States)

    Jeong, Hanbin; Lee, Jae Kwan

    2015-12-30

    A new organic-inorganic ternary bulk heterojunction (TBHJ) hybrid configuration comprised of nanostructured (CH3)3NHPbI3 (MAPbI3) perovskite-low bandgap PCPDTBT-PCBM was investigated. Well-organized TBHJ films were readily prepared by sequential spin-casting of sparsely covered MAPbI3 nano dots and PCPDTBT-PCBM bulk heterojunction (BHJ) composites on ITO/PEDOT:PSS substrates. The TBHJ hybrid device configuration comprising diiooctane (DIO) treated MAPbI3 perovskite nano dots and a PCPDTBT-PCBM BHJ composite processed with DIO additive exhibited excellent performances. The DIO additive played a key role in developing perovskite structures of MAPbI3 nano dots and induced the (110) directional crystallinity growth of longitudinal constructive morphologies such as nano rods. The improved photocurrent and fill factor compared to those of conventional BHJ devices led to an increase in efficiency of ∼28%. This improved photovoltaic performance originated from the higher quantum efficiencies contributed by the charge transfer from nanostructured MAPbI3 perovskite to PCBM. These TBHJs composed of nanostructured MAPbI3 perovskite, PCPDTBT, and PCBM also facilitated the exciton dissociation in the multi-BHJ system between MAPbI3 perovskite, PCPDTBT, and PCBM.

  6. Auger recombination in heavily doped shallow-emitter silicon p-n-junction solar cells, diodes, and transistors

    Science.gov (United States)

    Shibib, M. A.; Lindholm, F. A.; Fossum, J. G.

    1979-01-01

    A rigorous analytic evaluation of an emitter model that includes Auger recombination but excludes bandgap narrowing is presented. It is shown that such a model cannot explain the experimentally observed values of the open-circuit voltage in p-n-junction silicon solar cells. Thus physical mechanisms in addition to Auger recombination are responsible for the experimentally observed values of the open-circuit voltage in silicon solar cells and the common-emitter current gain in bipolar transistors.

  7. New Low-Bandgap Materials with Good Stabilities and Efficiencies Comparable to P3HT in R2R-Coated Solar Cells

    DEFF Research Database (Denmark)

    Søndergaard, Roar; Manceau, Matthieu; Jørgensen, Mikkel

    2012-01-01

    Roll-to-roll coated organic solar cells of two new polymers processed in ambient conditions show good photochemical stabilities, and their efficiencies are comparable to similar roll-to-roll coated P3HT cells. Optimal blend compositions are achieved by the use of differentially pumped slot die...

  8. Research on high-bandgap materials and amorphous silicon-based solar cells. Annual technical report, 15 May 1995--15 May 1996

    Energy Technology Data Exchange (ETDEWEB)

    Schiff, E.A.; Gu, Q.; Jiang, L.; Rao, P. [Syracuse, New York, NY (United States)

    1997-01-01

    We have developed a technique based on electroabsorption measurements for obtaining quantitative estimates of the built-in potential in a-Si:H based heterostructure solar cells incorporating microcrystalline or a-SiC:Hp layers. This heterostructure problem has been a major limitation in application of the electroabsorption technique. The new technique only utilizes measurements from a particular solar cell, and is thus a significant improvement on earlier techniques requiring measurements on auxiliary films. Using this new electroabsorption technique, we confirmed previous estimates of V{sub bi} {approx} 1.0 V in a-Si:H solar cells with {open_quotes}conventional{close_quotes} intrinsic layers and either microcrystalline or a-SiC:Hp layers. Interestingly, our first measurements on high V{sub oc} cells grown with {open_quotes}high hydrogen dilution{close_quotes} intrinsic layers yield a much larger value for V{sub bi} {approx} 1.3 V. We speculate that these results are evidence for a significant interface dipole at the p/i heterostructure interface. Although we believe that interface dipoles rationalize several previously unexplained effects on a-Si:H based cells, they are not currently included in models for the operation of a-Si:H based solar cells.

  9. Organic ternary solar cells: a review.

    Science.gov (United States)

    Ameri, Tayebeh; Khoram, Parisa; Min, Jie; Brabec, Christoph J

    2013-08-21

    Recently, researchers have paid a great deal of attention to the research and development of organic solar cells, leading to a breakthrough of over 10% power conversion efficiency. Though impressive, further development is required to ensure a bright industrial future for organic photovoltaics. Relatively narrow spectral overlap of organic polymer absorption bands within the solar spectrum is one of the major limitations of organic solar cells. Among different strategies that are in progress to tackle this restriction, the novel concept of ternary organic solar cells is a promising candidate to extend the absorption spectra of large bandgap polymers to the near IR region and to enhance light harvesting in single bulk-heterojunction solar cells. In this contribution, we review the recent developments in organic ternary solar cell research based on various types of sensitizers. In addition, the aspects of miscibility, morphology complexity, charge transfer dynamics as well as carrier transport in ternary organic composites are addressed.

  10. Band gap narrowing and photocatalytic studies of Nd3+ ion-doped SnO2 nanoparticles using solar energy

    Indian Academy of Sciences (India)

    Dhanya Chandran; Lakshmi S Nair; S Balachandran; K Rajendra Babu; M Deepa

    2016-02-01

    Pure and Nd3+-doped tin oxide (SnO2) nanoparticles have been prepared by the sol–gel method and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution TEM, energydispersive spectroscopy and UV–visible spectroscopy. The XRD patterns of all the samples are identified as tetragonal rutile-type SnO2 phase which is further confirmed by TEM analysis. Neodymium doping introduces band gap narrowing in the prepared samples and enhances their absorption towards the visible-light region. The photocatalytic activity of all the samples was evaluated by monitoring the degradation of methylene blue solution under day light illumination and it was found that the photocatalytic activity significantly increases for the samples calcined at 600 than 400°C, which is due to the effective charge separation of photogenerated electron–hole pairs. The efficiency of photocatalysts was found to be related to neodymium doping percentage and calcination temperature.

  11. Research on High-Bandgap Materials and Amorphous Silicon-Based Solar Cells, Final Technical Report, 15 May 1994-15 January 1998

    Energy Technology Data Exchange (ETDEWEB)

    Schiff, E. A.; Gu, Q.; Jiang, L.; Lyou, J.; Nurdjaja, I.; Rao, P. (Department of Physics, Syracuse University)

    1998-12-28

    This report describes work performed by Syracuse University under this subcontract. Researchers developed a technique based on electroabsorption measurements for obtaining quantitative estimates of the built-in potential Vbi in a-Si:H-based heterostructure solar cells incorporating microcrystalline or a-SiC:H p layers. Using this new electroabsorption technique, researchers confirmed previous estimates of Vbi {yields} 1.0 V in a-Si:H solar cells with ''conventional'' intrinsic layers and either microcrystalline or a-SiC:H p layers. Researchers also explored the recent claim that light-soaking of a-Si:H substantially changes the polarized electroabsorption associated with interband optical transitions (and hence, not defect transitions). Researchers confirmed measurements of improved (5') hole drift mobilities in some specially prepared a-Si:H samples. Disturbingly, solar cells made with such materials did not show improved efficiencies. Researchers significantly clarified the relationship of ambipolar diffusion-length measurements to hole drift mobilities in a-Si:H, and have shown that the photocapacitance measurements can be interpreted in terms of hole drift mobilities in amorphous silicon. They also completed a survey of thin BP:H and BPC:H films prepared by plasma deposition using phosphine, diborane, trimethylboron, and hydrogen as precursor gases.

  12. The density matrix method in photonic bandgap and antiferromagnetic materials

    Science.gov (United States)

    Barrie, Scott B.

    In this thesis, a theory for dispersive polaritonic bandgap (DPBG) and photonic bandgap (PBG) materials is developed. An ensemble of multi-level nanoparticles, such as non-interacting two-, three- and four-level atoms doped in DPBG and PBG materials is considered. The optical properties of these materials such as spontaneous emission, line broadening, fluorescence and narrowing of the natural linewidth have been studied using the density matrix method. Numerical simulations for these properties have been performed for the DPBG materials SiC and InAs, and for a PBG material with a 20 percent gap-to-midgap ratio. When a three-level nanoparticle is doped into a DPBG material, it is predicted that one or two bound states exist when one or both resonance energies, respectively, lie in the bandgap. It is shown when a resonance energy lies below the bandgap, its spectral density peak weakens and broadens as the resonance energy increases to the lower band edge. For the first time it is predicted that when a nanoparticle's resonance energy lies above the bandgap, its spectral density peak weakens and broadens as the resonance energy increases. A relation is also found between spectral structure and gap-to-midgap ratios. The dressed states of a two-level atom doped into a DPBG material under the influence of an intense monochromatic laser field are examined. The splitting of the dressed state energies is calculated, and it is predicted that the splitting depends on the polariton density of states and the Rabi frequency of laser field. The fluoresence is also examined, and for the first time two distinct control processes are found for the transition from one peak to three peaks. It was previously known that the Rabi frequency controlled the Stark effect, but this thesis predicts that the local of the peak with respect to the optical bandgap can cause a transition from one to three peaks even with a weak Rabi frequency. The transient linewidth narrowing of PBG crystal

  13. Thiophene-rich fused-aromatic thienopyrazine acceptor for donor–acceptor low band-gap polymers for OTFT and polymer solar cell applications

    KAUST Repository

    Mondal, Rajib

    2010-01-01

    Thiophene enriched fused-aromatic thieno[3,4-b]pyrazine systems were designed and employed to produce low band gap polymers (Eg = 1.0-1.4 eV) when copolymerized with fluorene and cyclopentadithiophene. The copolymers are mainly investigated for organic thin film transistor and organic photovoltaic applications. Molecular packing in the thin films of these polymers was investigated using Grazing incidence X-ray Scattering. Although both fluorene and cyclopentadithiophene polymers follow similar face to face π-π stacking, the latter polymers show much smaller lamellar d-spacings due to side-chain interdigitation between the lamellae. This lead to the higher charge carrier mobilities in cyclopentadithiophene polymers (up to 0.044 cm2/V.s) compared to fluorene polymers (up to 8.1 × 10-3 cm2/V.s). Power conversion efficiency of 1.4% was achieved using fluorene copolymer in solar cells with a fullerene derivative as an acceptor. Although the cyclopentadithiophene polymers show lower band gaps with higher absorption coefficients compared to fluorene copolymers, but the power conversion efficiencies in solar cells of these polymers are low due to their low ionization potentials. © The Royal Society of Chemistry 2010.

  14. Dye- and quantum dot-sensitized solar cells based on nanostructured wide-bandgap semiconductors via an integrated experimental and modeling study

    Science.gov (United States)

    Xin, Xukai

    Dye-sensitized solar cells (DSSCs) and quantum dot-sensitized solar cells (QDSSCs) are two promising alternative, cost-effective concepts for solar-to-electric energy conversion that have been offered to challenge conventional Si solar cells over the past decade. The configuration of a DSSC or a QDSSC consists of sintered TiO2 nanoparticle films, ruthenium-based dyes or quantum dots (QDs) (i.e., sensitizers), and electrolytes. Upon the absorption of photons, the dyes or QDs generate excitons (i.e., electron-hole pairs). Subsequently, the electrons inject into the TiO2 photoanode to generate photocurrent; scavenged by a redox couple, holes transport to the cathode. The overall power conversion efficiency (PCE) of a DSSC or QDSSC is dictated by the light harvest efficiency, quantum yield for charge injection, and charge collection efficiency at the electrodes. The goal of our research is to understand the fundamental physics and performance of DSSCs and QDSSCs with improved PCE at the low cost based on rational engineering of TiO2 nanostructures, sensitizers, and electrodes through an integrated experimental and modeling study. In this presentation, I will discuss three aspects that I have accomplished over the last several years. (1) Effects of surface treatment and structural modification of photoanode on the performance of DSSCs. First, our research indicates that the surface treatment with both TiCl4 and oxygen plasma yields the most efficient dye-sensitized TiO2-nanoparticle solar cells. A maximum PCE is achieved with a 21 microm thick TiO2 film; the PCE further increases to 8.35% after TiCl4 and O 2 plasma treatments, compared to the untreated TiO2 ( PCE = 3.86%). Second, we used a layer of TiO2 nanoparticle film coated on the FTO glass, and a bilayer of TiO2nanoparticle/freestanding TiO2 nanotube film deposited on the FTO glass as photoanodes. The J˜V parameter analysis acquired by equivalent circuit model simulation reveals that nanotubular structures are

  15. Solar cell efficiency, self-assembly, and dipole-dipole interactions of isomorphic narrow-band-gap molecules.

    Science.gov (United States)

    Takacs, Christopher J; Sun, Yanming; Welch, Gregory C; Perez, Louis A; Liu, Xiaofeng; Wen, Wen; Bazan, Guillermo C; Heeger, Alan J

    2012-10-10

    We examine the correlations of the dipole moment and conformational stability to the self-assembly and solar cell performance within a series of isomorphic, solution-processable molecules. These charge-transfer chromophores are described by a D(1)-A-D-A-D(1) structure comprising electron-rich 2-hexylbithiophene and 3,3'-di-2-ethylhexylsilylene-2,2'-bithiophene moieties as the donor units D(1) and D, respectively. The building blocks 2,1,3-benzothiadiazole (BT) and [1,2,5]thiadiazolo[3,4-c]pyridine (PT) were used as the electron-deficient acceptor units A. Using a combination of UV-visible spectroscopy, field-effect transistors, solar cell devices, grazing incident wide-angle X-ray scattering, and transmission electron microscopy, three PT-containing compounds (1-3) with varying regiochemistry and symmetry, together with the BT-based compound 5,5'-bis{(4-(7-hexylthiophen-2-yl)thiophen-2-yl)-[1,2,5]thiadiazolobenzene}-3,3'-di-2-ethylhexylsilylene-2,2'-bithiophene (4), are compared and contrasted in solution, in thin films, and as blends with the electron acceptor [6,6]-phenyl-C(70)-butyric acid methyl ester. The molecules with symmetric orientations of the PT acceptor, 1 and 2, yield highly ordered blended thin films. The best films, processed with the solvent additive 1,8-diiodooctane, show donor "crystallite" length scales on the order of 15-35 nm and photovoltaic power conversion efficiencies (PCEs) of 7.0 and 5.6%, respectively. Compound 3, with an unsymmetrical orientation of PT heterocycles, shows subtle differences in the crystallization behavior and a best PCE of 3.2%. In contrast, blends of the BT-containing donor 4 are highly disordered and give PCEs below 0.2%. We speculate that the differences in self-assembly arise from the strong influence of the BT acceptor and its orientation on the net dipole moment and geometric description of the chromophore.

  16. Densely Aligned Graphene Nanoribbon Arrays and Bandgap Engineering

    Energy Technology Data Exchange (ETDEWEB)

    Su, Justin [Stanford Univ., CA (United States); Chen, Changxin [Stanford Univ., CA (United States); Gong, Ming [Stanford Univ., CA (United States); Kenney, Michael [Stanford Univ., CA (United States)

    2017-01-04

    Graphene has attracted great interest for future electronics due to its high mobility and high thermal conductivity. However, a two-dimensional graphene sheet behaves like a metal, lacking a bandgap needed for the key devices components such as field effect transistors (FETs) in digital electronics. It has been shown that, partly due to quantum confinement, graphene nanoribbons (GNRs) with ~2 nm width can open up sufficient bandgaps and evolve into semiconductors to exhibit high on/off ratios useful for FETs. However, a challenging problem has been that, such ultra-narrow GNRs (~2 nm) are difficult to fabricate, especially for GNRs with smooth edges throughout the ribbon length. Despite high on/off ratios, these GNRs show very low mobility and low on-state conductance due to dominant scattering effects by imperfections and disorders at the edges. Wider GNRs (>5 nm) show higher mobility, higher conductance but smaller bandgaps and low on/off ratios undesirable for FET applications. It is highly desirable to open up bandgaps in graphene or increase the bandgaps in wide GNRs to afford graphene based semiconductors for high performance (high on-state current and high on/off ratio) electronics. Large scale ordering and dense packing of such GNRs in parallel are also needed for device integration but have also been challenging thus far. It has been shown theoretically that uniaxial strains can be applied to a GNR to engineer its bandgap. The underlying physics is that under uniaxial strain, the Dirac point moves due to stretched C-C bonds, leading to an increase in the bandgap of armchair GNRs by up to 50% of its original bandgap (i.e. bandgap at zero strain). For zigzag GNRs, due to the existence of the edge states, changes of bandgap are smaller under uniaxial strain and can be increased by ~30%. This work proposes a novel approach to the fabrication of densely aligned graphene nanoribbons with highly smooth edges afforded by anisotropic etching and uniaxial strain for

  17. Interdigitated back contact solar cells

    Science.gov (United States)

    Lundstrom, M. S.; Schwartz, R. J.

    1980-08-01

    The interdigitated back contact solar cell (IBC cell) was shown to possess a number of advantages for silicon solar cells, which operate at high concentration. A detailed discussion of the factors which need to be considered in the analysis of semiconducting devices which utilize heavily doped regions such as those which are found in solar cells in both the emitter and in the back surface field regions is given. This discussion covers the questions of: how to handle degeneracy, how to compute carrier concentrations in the absence of knowledge of the details of the band structure under heavily doped conditions, and how to reconcile the usual interpretation of heavy doping as a rigid shift of the bands with the band tailing and impurity level conduction models. It also discusses the reasons for the observed discrepancies between various experimental measurements of bandgap narrowing.

  18. Wide-Bandgap Semiconductors

    Energy Technology Data Exchange (ETDEWEB)

    Chinthavali, M.S.

    2005-11-22

    With the increase in demand for more efficient, higher-power, and higher-temperature operation of power converters, design engineers face the challenge of increasing the efficiency and power density of converters [1, 2]. Development in power semiconductors is vital for achieving the design goals set by the industry. Silicon (Si) power devices have reached their theoretical limits in terms of higher-temperature and higher-power operation by virtue of the physical properties of the material. To overcome these limitations, research has focused on wide-bandgap materials such as silicon carbide (SiC), gallium nitride (GaN), and diamond because of their superior material advantages such as large bandgap, high thermal conductivity, and high critical breakdown field strength. Diamond is the ultimate material for power devices because of its greater than tenfold improvement in electrical properties compared with silicon; however, it is more suited for higher-voltage (grid level) higher-power applications based on the intrinsic properties of the material [3]. GaN and SiC power devices have similar performance improvements over Si power devices. GaN performs only slightly better than SiC. Both SiC and GaN have processing issues that need to be resolved before they can seriously challenge Si power devices; however, SiC is at a more technically advanced stage than GaN. SiC is considered to be the best transition material for future power devices before high-power diamond device technology matures. Since SiC power devices have lower losses than Si devices, SiC-based power converters are more efficient. With the high-temperature operation capability of SiC, thermal management requirements are reduced; therefore, a smaller heat sink would be sufficient. In addition, since SiC power devices can be switched at higher frequencies, smaller passive components are required in power converters. Smaller heat sinks and passive components result in higher-power-density power converters

  19. Bifacial tandem solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Wojtczuk, Steven J.; Chiu, Philip T.; Zhang, Xuebing; Gagnon, Edward; Timmons, Michael

    2016-06-14

    A method of fabricating on a semiconductor substrate bifacial tandem solar cells with semiconductor subcells having a lower bandgap than the substrate bandgap on one side of the substrate and with subcells having a higher bandgap than the substrate on the other including, first, growing a lower bandgap subcell on one substrate side that uses only the same periodic table group V material in the dislocation-reducing grading layers and bottom subcells as is present in the substrate and after the initial growth is complete and then flipping the substrate and growing the higher bandgap subcells on the opposite substrate side which can be of different group V material.

  20. Low-bandgap, monolithic, multi-bandgap, optoelectronic devices

    Science.gov (United States)

    Wanlass, Mark W.; Carapella, Jeffrey J.

    2014-07-08

    Low bandgap, monolithic, multi-bandgap, optoelectronic devices (10), including PV converters, photodetectors, and LED's, have lattice-matched (LM), double-heterostructure (DH), low-bandgap GaInAs(P) subcells (22, 24) including those that are lattice-mismatched (LMM) to InP, grown on an InP substrate (26) by use of at least one graded lattice constant transition layer (20) of InAsP positioned somewhere between the InP substrate (26) and the LMM subcell(s) (22, 24). These devices are monofacial (10) or bifacial (80) and include monolithic, integrated, modules (MIMs) (190) with a plurality of voltage-matched subcell circuits (262, 264, 266, 270, 272) as well as other variations and embodiments.

  1. Low-bandgap, monolithic, multi-bandgap, optoelectronic devices

    Energy Technology Data Exchange (ETDEWEB)

    Wanlass, Mark W.; Carapella, Jeffrey J.

    2016-01-05

    Low bandgap, monolithic, multi-bandgap, optoelectronic devices (10), including PV converters, photodetectors, and LED's, have lattice-matched (LM), double-heterostructure (DH), low-bandgap GaInAs(P) subcells (22, 24) including those that are lattice-mismatched (LMM) to InP, grown on an InP substrate (26) by use of at least one graded lattice constant transition layer (20) of InAsP positioned somewhere between the InP substrate (26) and the LMM subcell(s) (22, 24). These devices are monofacial (10) or bifacial (80) and include monolithic, integrated, modules (MIMs) (190) with a plurality of voltage-matched subcell circuits (262, 264, 266, 270, 272) as well as other variations and embodiments.

  2. Low-bandgap, monolithic, multi-bandgap, optoelectronic devices

    Energy Technology Data Exchange (ETDEWEB)

    Wanlass, Mark W.; Carapella, Jeffrey J.

    2014-07-08

    Low bandgap, monolithic, multi-bandgap, optoelectronic devices (10), including PV converters, photodetectors, and LED's, have lattice-matched (LM), double-heterostructure (DH), low-bandgap GaInAs(P) subcells (22, 24) including those that are lattice-mismatched (LMM) to InP, grown on an InP substrate (26) by use of at least one graded lattice constant transition layer (20) of InAsP positioned somewhere between the InP substrate (26) and the LMM subcell(s) (22, 24). These devices are monofacial (10) or bifacial (80) and include monolithic, integrated, modules (MIMs) (190) with a plurality of voltage-matched subcell circuits (262, 264, 266, 270, 272) as well as other variations and embodiments.

  3. Low-bandgap, monolithic, multi-bandgap, optoelectronic devices

    Energy Technology Data Exchange (ETDEWEB)

    Wanlass, Mark W.; Carapella, Jeffrey J.

    2016-03-22

    Low bandgap, monolithic, multi-bandgap, optoelectronic devices (10), including PV converters, photodetectors, and LED's, have lattice-matched (LM), double-heterostructure (DH), low-bandgap GaInAs(P) subcells (22, 24) including those that are lattice-mismatched (LMM) to InP, grown on an InP substrate (26) by use of at least one graded lattice constant transition layer (20) of InAsP positioned somewhere between the InP substrate (26) and the LMM subcell(s) (22, 24). These devices are monofacial (10) or bifacial (80) and include monolithic, integrated, modules (MIMs) (190) with a plurality of voltage-matched subcell circuits (262, 264, 266, 270, 272) as well as other variations and embodiments.

  4. Composition and bandgap-graded semiconductor alloy nanowires.

    Science.gov (United States)

    Zhuang, Xiujuan; Ning, C Z; Pan, Anlian

    2012-01-03

    Semiconductor alloy nanowires with spatially graded compositions (and bandgaps) provide a new material platform for many new multifunctional optoelectronic devices, such as broadly tunable lasers, multispectral photodetectors, broad-band light emitting diodes (LEDs) and high-efficiency solar cells. In this review, we will summarize the recent progress on composition graded semiconductor alloy nanowires with bandgaps graded in a wide range. Depending on different growth methods and material systems, two typical nanowire composition grading approaches will be presented in detail, including composition graded alloy nanowires along a single substrate and those along single nanowires. Furthermore, selected examples of applications of these composition graded semiconductor nanowires will be presented and discussed, including tunable nanolasers, multi-terminal on-nanowire photodetectors, full-spectrum solar cells, and white-light LEDs. Finally, we will make some concluding remarks with future perspectives including opportunities and challenges in this research area.

  5. Polarization properties of photonic bandgap fibers

    DEFF Research Database (Denmark)

    Broeng, Jes; Libori, Stig E. Barkou; Bjarklev, Anders Overgaard

    2000-01-01

    We present the first analysis of polarization properties of photonic bandgap fibers. Strong birefringence may be obtained for modest non-uniformities in and around the core region, suggesting the use of photonic bandgap fibers as polarization maintaining components.......We present the first analysis of polarization properties of photonic bandgap fibers. Strong birefringence may be obtained for modest non-uniformities in and around the core region, suggesting the use of photonic bandgap fibers as polarization maintaining components....

  6. Study of microcrystalline silicon-germanium solar cell with wide-spectrum and narrow-bandgap%宽光谱窄带隙微晶硅锗太阳电池研究

    Institute of Scientific and Technical Information of China (English)

    刘群; 倪牮; 张建军; 马峻; 王昊; 赵颖

    2015-01-01

    采用射频等离子体增强化学气相沉积(RF-PECVD)技术,制备了高锗含量(原子百分含量)的氢化微晶硅锗(μc-Si1-xGex:H)材料.通过锗含量、拉曼光谱、吸收系数以及电导率测试,研究了不同离子轰击条件下μc-Si1-xGex:H薄膜的结构及光电性能.在高离子轰击条件下制备的高锗含量的μc-Si1xGex:H薄膜显示,锗的掺入速度有所降低,晶化率和吸收系数较高且光敏性明显提高;本征层锗含量x=77%的μc-Si1 Gex:H太阳电池的量子效率在长波段显著增强且光谱响应拓展至1 300 nm,此时电池效率达到3.16%.

  7. Wide Bandgap Extrinsic Photoconductive Switches

    Energy Technology Data Exchange (ETDEWEB)

    Sullivan, James S. [State Univ. of New York (SUNY), Plattsburgh, NY (United States); Univ. of California, Davis, CA (United States)

    2012-01-20

    Photoconductive semiconductor switches (PCSS) have been investigated since the late 1970s. Some devices have been developed that withstand tens of kilovolts and others that switch hundreds of amperes. However, no single device has been developed that can reliably withstand both high voltage and switch high current. Yet, photoconductive switches still hold the promise of reliable high voltage and high current operation with subnanosecond risetimes. Particularly since good quality, bulk, single crystal, wide bandgap semiconductor materials have recently become available. In this chapter we will review the basic operation of PCSS devices, status of PCSS devices and properties of the wide bandgap semiconductors 4H-SiC, 6H-SiC and 2H-GaN.

  8. Wide Bandgap Extrinsic Photoconductive Switches

    Energy Technology Data Exchange (ETDEWEB)

    Sullivan, James S. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

    2013-07-03

    Semi-insulating Gallium Nitride, 4H and 6H Silicon Carbide are attractive materials for compact, high voltage, extrinsic, photoconductive switches due to their wide bandgap, high dark resistance, high critical electric field strength and high electron saturation velocity. These wide bandgap semiconductors are made semi-insulating by the addition of vanadium (4H and 6HSiC) and iron (2H-GaN) impurities that form deep acceptors. These deep acceptors trap electrons donated from shallow donor impurities. The electrons can be optically excited from these deep acceptor levels into the conduction band to transition the wide bandgap semiconductor materials from a semi-insulating to a conducting state. Extrinsic photoconductive switches with opposing electrodes have been constructed using vanadium compensated 6H-SiC and iron compensated 2H-GaN. These extrinsic photoconductive switches were tested at high voltage and high power to determine if they could be successfully used as the closing switch in compact medical accelerators.

  9. Photonic Bandgaps in Photonic Molecules

    Science.gov (United States)

    Smith, David D.; Chang, Hongrok; Gates, Amanda L.; Fuller, Kirk A.; Gregory, Don A.; Witherow, William K.; Paley, Mark S.; Frazier, Donald O.; Curreri, Peter A. (Technical Monitor)

    2002-01-01

    This talk will focus on photonic bandgaps that arise due to nearly free photon and tight-binding effects in coupled microparticle and ring-resonator systems. The Mie formulation for homogeneous spheres is generalized to handle core/shell systems and multiple concentric layers in a manner that exploits an analogy with stratified planar systems, thereby allowing concentric multi-layered structures to be treated as photonic bandgap (PBG) materials. Representative results from a Mie code employing this analogy demonstrate that photonic bands arising from nearly free photon effects are easily observed in the backscattering, asymmetry parameter, and albedo for periodic quarter-wave concentric layers, though are not readily apparent in extinction spectra. Rather, the periodicity simply alters the scattering profile, enhancing the ratio of backscattering to forward scattering inside the bandgap, in direct analogy with planar quarter-wave multilayers. PBGs arising from tight-binding may also be observed when the layers (or rings) are designed such that the coupling between them is weak. We demonstrate that for a structure consisting of N coupled micro-resonators, the morphology dependent resonances split into N higher-Q modes, in direct analogy with other types of oscillators, and that this splitting ultimately results in PBGs which can lead to enhanced nonlinear optical effects.

  10. A theory of the n-i-p silicon solar cell

    Science.gov (United States)

    Goradia, C.; Weinberg, I.; Baraona, C.

    1981-01-01

    A computer model has been developed, based on an analytical theory of the high base resistivity BSF n(+)(pi)p(+) or p(+)(nu)n(+) silicon solar cell. The model makes very few assumptions and accounts for nonuniform optical generation, generation and recombination in the junction space charge region, and bandgap narrowing in the heavily doped regions. The paper presents calculated results based on this model and compares them to available experimental data. Also discussed is radiation damage in high base resistivity n(+)(pi)p(+) space solar cells.

  11. Effect of recombination on the open-circuit voltage of a silicon solar cell

    Science.gov (United States)

    Von Roos, O.; Landsberg, P. T.

    1985-01-01

    A theoretical study of the influence of band-band Auger, band-trap Auger, and the ordinary Shockley-Read-Hall mechanism for carrier recombination on the open-circuit voltage VOC of a solar cell is presented. Under reasonable assumptions for the magnitude of rate constants and realistic values for trap densities, surface recombination velocities and band-gap narrowing, the maximum VOC for typical back surface field solar cells is found to lie in the range between 0.61 and 0.72 V independent of base width.

  12. Bandgap modulation of carbon nanotubes by encapsulated metallofullerenes

    Science.gov (United States)

    Lee, Jhinhwan; Kim, H.; Kahng, S.-J.; Kim, G.; Son, Y.-W.; Ihm, J.; Kato, H.; Wang, Z. W.; Okazaki, T.; Shinohara, H.; Kuk, Young

    2002-02-01

    Motivated by the technical and economic difficulties in further miniaturizing silicon-based transistors with the present fabrication technologies, there is a strong effort to develop alternative electronic devices, based, for example, on single molecules. Recently, carbon nanotubes have been successfully used for nanometre-sized devices such as diodes, transistors, and random access memory cells. Such nanotube devices are usually very long compared to silicon-based transistors. Here we report a method for dividing a semiconductor nanotube into multiple quantum dots with lengths of about 10nm by inserting Gd@C82 endohedral fullerenes. The spatial modulation of the nanotube electronic bandgap is observed with a low-temperature scanning tunnelling microscope. We find that a bandgap of ~0.5eV is narrowed down to ~0.1eV at sites where endohedral metallofullerenes are inserted. This change in bandgap can be explained by local elastic strain and charge transfer at metallofullerene sites. This technique for fabricating an array of quantum dots could be used for nano-electronics and nano-optoelectronics.

  13. Elucidating interactions and conductivity of newly synthesised low bandgap polymer with protic and aprotic ionic liquids.

    Directory of Open Access Journals (Sweden)

    Pankaj Attri

    Full Text Available In this paper, we have examined the conductivity and interaction studies of ammonium and imidazolium based ionic liquids (ILs with the newly synthesised low bandgap polymer (Poly(2-heptadecyl-4-vinylthieno[3,4-d]thiazole (PHVTT. Use of low bandgap polymers is the most suitable way to harvest a broader spectrum of solar radiations for solar cells. But, still there is lack of most efficient low bandgap polymer. In order to solve this problem, we have synthesised a new low bandgap polymer and investigated its interaction with the ILs to enhance its conductivity. ILs may undergo almost unlimited structural variations; these structural variations have attracted extensive attention in polymer studies. The aim of present work is to illustrate the state of art progress of implementing the interaction of ILs (protic and aprotic ILs with newly synthesised low bandgap polymer. In addition to this, our UV-Vis spectroscopy, confocal Raman spectroscopy and FT-IR spectroscopy results have revealed that all studied ILs (tributylmethylammonium methyl sulfate ([N1444][MeSO4] from ammonium family and 1-methylimidazolium chloride ([Mim]Cl, and 1-butyl-3-methylimidazolium chloride ([Bmim]Cl from imidazolium family have potential to interact with polymer. Our semi empirical calculation with help of Hyperchem 7 shows that protic IL ([Mim]Cl interacts strongly with the low bandgap polymer through the H-bonding. Further, protic ILs shows enhanced conductivity than aprotic ILs in association with low bandgap polymer. This study provides the combined effect of low bandgap polymer and ILs that may generate many theoretical and experimental opportunities.

  14. Machine learning bandgaps of double perovskites

    National Research Council Canada - National Science Library

    Pilania, G; Mannodi-Kanakkithodi, A; Uberuaga, B P; Ramprasad, R; Gubernatis, J E; Lookman, T

    2016-01-01

    .... While quantum mechanical computations for high-fidelity bandgaps are enormously computation-time intensive and thus impractical in high throughput studies, informatics-based statistical learning...

  15. Application of closed-form solutions to a mesh point field in silicon solar cells

    Science.gov (United States)

    Lamorte, M. F.

    1985-01-01

    A computer simulation method is discussed that provides for equivalent simulation accuracy, but that exhibits significantly lower CPU running time per bias point compared to other techniques. This new method is applied to a mesh point field as is customary in numerical integration (NI) techniques. The assumption of a linear approximation for the dependent variable, which is typically used in the finite difference and finite element NI methods, is not required. Instead, the set of device transport equations is applied to, and the closed-form solutions obtained for, each mesh point. The mesh point field is generated so that the coefficients in the set of transport equations exhibit small changes between adjacent mesh points. Application of this method to high-efficiency silicon solar cells is described; and the method by which Auger recombination, ambipolar considerations, built-in and induced electric fields, bandgap narrowing, carrier confinement, and carrier diffusivities are treated. Bandgap narrowing has been investigated using Fermi-Dirac statistics, and these results show that bandgap narrowing is more pronounced and that it is temperature-dependent in contrast to the results based on Boltzmann statistics.

  16. Optoelectronic devices based on graded bandgap structures utilising electroplated semiconductors

    OpenAIRE

    2016-01-01

    The main aim of the work presented in this thesis is to develop low-cost multi-junction graded bandgap solar cells using electroplated semiconductors. The semiconductor materials explored in this research are CdSe, ZnTe, CdS, CdMnTe and CdTe thin films. These layers were characterised for their structural, compositional, morphological, optical, and electrical features using XRD, Raman spectroscopy, EDX, SEM, UV-Vis spectroscopy, PEC cell, C-V, I-V and UPS measurement techniques respectively. ...

  17. The Search for Sub-Bandgap Optoelectronic Response in Silicon Hyperdoped with Gold

    Science.gov (United States)

    Mailoa, Jonathan; Akey, Austin; Mathews, Jay; Hutchinson, David; Simmons, Christie; Sullivan, Joseph; Winkler, Mark; Recht, Dan; Persans, Peter; Warrender, Jeffrey; Aziz, Michael; Buonassisi, Tonio

    2013-03-01

    Deep-level dopants have been long known as the lifetime-killer in microelectronic devices. Nevertheless, it has been shown that deep-level donor can facilitate strong absorption of light with energy below the semiconductor bandgap. Due to this strong sub-bandgap absorption, it is possible to engineer silicon devices exhibiting sub-bandgap optoelectronic response, such as silicon-based infrared photodetectors and intermediate-band solar cells. In this work, we show the optoelectronic response of silicon doped with a gold concentration surpassing the equilibrium solubility limit (gold-hyperdoped silicon, Au:Si). We fabricated Au:Si by ion implantation followed by nanosecond pulse laser melting, achieving a gold dopant concentration of over 1019 cm-3. UV-VIS spectrophotometry was performed to measure sub-bandgap light absorption in the Au:Si layer. Our samples with the highest gold concentration have 10-15% absorption of sub-bandgap light. We will present and discuss the sub-bandgap optoelectronic response of this gold-doped silicon.

  18. Studies of silicon pn junction solar cells

    Science.gov (United States)

    Lindholm, F. A.; Neugroschel, A.

    1977-01-01

    Modifications of the basic Shockley equations that result from the random and nonrandom spatial variations of the chemical composition of a semiconductor were developed. These modifications underlie the existence of the extensive emitter recombination current that limits the voltage over the open circuit of solar cells. The measurement of parameters, series resistance and the base diffusion length is discussed. Two methods are presented for establishing the energy bandgap narrowing in the heavily-doped emitter region. Corrections that can be important in the application of one of these methods to small test cells are examined. Oxide-charge-induced high-low-junction emitter (OCI-HLE) test cells which exhibit considerably higher voltage over the open circuit than was previously seen in n-on-p solar cells are described.

  19. TiO2 anatase with a bandgap in the visible region.

    Science.gov (United States)

    Dette, Christian; Pérez-Osorio, Miguel A; Kley, Christopher S; Punke, Paul; Patrick, Christopher E; Jacobson, Peter; Giustino, Feliciano; Jung, Soon Jung; Kern, Klaus

    2014-11-12

    TiO2 anatase plays a central role in energy and environmental research. A major bottleneck toward developing artificial photosynthesis with TiO2 is that it only absorbs ultraviolet light, owing to its large bandgap of 3.2 eV. If one could reduce the bandgap of anatase to the visible region, TiO2-based photocatalysis could become a competitive clean energy source. Here, using scanning tunneling microscopy and spectroscopy in conjunction with density functional theory calculations, we report the discovery of a highly reactive titanium-terminated anatase surface with a reduced bandgap of less than 2 eV, stretching into the red portion of the solar spectrum. By tuning the surface preparation conditions, we can reversibly switch between the standard anatase surface and the newly discovered low bandgap surface phase. The identification of a TiO2 anatase surface phase with a bandgap in the visible and high chemical reactivity has important implications for solar energy conversion, photocatalysis, and artificial photosynthesis.

  20. Novel Approaches to Wide Bandgap CuInSe2 Based Absorbers

    Energy Technology Data Exchange (ETDEWEB)

    William N. Shafarman

    2011-04-28

    This project targeted the development of high performance wide bandgap solar cells based on thin film alloys of CuInSe2 to relax constraints on module design and enable tandem solar cell structures. This addressed goals of the Solar Energy Technologies Program for Next Generation PV to develop technology needed for higher thin film module efficiency as a means to reduce costs. Specific objectives of the research project were: 1) to develop the processes and materials required to improve the performance of wide bandgap thin film solar cells based on alloys of CuInSe2, and 2) to provide the fundamental science and engineering basis for the material, electronic, and device properties required to effectively apply these processes and materials to commercial manufacture. CuInSe2-based photovoltaics have established the highest efficiencies of the thin film materials at both the cell and module scales and are actively being scaled up to commercialization. In the highest efficiency cells and modules, the optical bandgap, a function of the CuInSe2-based alloy composition, is relatively low compared to the optimum match to the solar spectrum. Wider bandgap alloys of CuInSe2 produce higher cell voltages which can improve module performance and enable the development of tandem solar cells to boost the overall efficiency. A focus for the project was alloying with silver to form (AgCu)(InGa)Se2 pentenary thin films deposited by elemental co-evaporation which gives the broadest range of control of composition and material properties. This alloy has a lower melting temperature than Ag-free, Cu-based chalcopyrite compounds, which may enable films to be formed with lower defect densities and the (AgCu)(InGa)Se2 films give improved material properties and better device performance with increasing bandgap. A comprehensive characterization of optical, structural, and electronic properties of (AgCu)(InGa)Se2 was completed over the complete compositional range 0 ≤ Ga/(In+Ga) ≤ 1 and

  1. Method of fabricating bifacial tandem solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Wojtczuk, Steven J; Chiu, Philip T; Zhang, Xuebing; Gagnon, Edward; Timmons, Michael

    2014-10-07

    A method of fabricating on a semiconductor substrate bifacial tandem solar cells with semiconductor subcells having a lower bandgap than the substrate bandgap on one side of the substrate and with subcells having a higher bandgap than the substrate on the other including, first, growing a lower bandgap subcell on one substrate side that uses only the same periodic table group V material in the dislocation-reducing grading layers and bottom subcells as is present in the substrate and after the initial growth is complete and then flipping the substrate and growing the higher bandgap subcells on the opposite substrate side which can be of different group V material.

  2. Application and comparison of band gap narrowing models for passivated phosphorus doped silicon surfaces

    Science.gov (United States)

    Kimmerle, Achim; Greulich, Johannes; Haug, Halvard; Wolf, Andreas

    2016-01-01

    In this work, the recently proposed band-gap narrowing model by Yan and Cuevas [J. Appl. Phys. 114, 044508 (2013)] is evaluated by simulations of the recombination pre-factor J0 of highly phosphorus doped, passivated crystalline silicon surfaces, which are particularly relevant for solar cell applications. The results were fitted to experimental J0 data measured on a large range of samples exhibiting different dopant profiles and passivation coatings, both for planar and textured surfaces. For each sample, the surface recombination velocity parameter Sp was extracted by fitting the simulation results to the experimental data. We show that the Yan and Cuevas' model developed for Fermi-Dirac statistics leads to a smooth and monotonically increasing curve for Sp as a function of the surface dopant concentration Nsurf, for both investigated passivation layers. We provide a parameterization for this relation and compare the findings with those obtained with the widely used model by Schenk [J. Appl. Phys. 84, 3684 (1998)]. On the other hand, we show that the apparent band gap narrowing of Yan and Cuevas developed for use with Boltzmann statistics cannot be used to describe the experimental data, requiring unphysical negative Sp values for high Nsurf.

  3. Actively doped solid core Photonic Bandgap Fiber

    DEFF Research Database (Denmark)

    Broeng, Jes; Olausson, Christina Bjarnal Thulin; Lyngsøe, Jens Kristian;

    2010-01-01

    Solid photonic bandgap fibers offer distributed spectral filtering with extraordinary high suppression. This opens new possibilities of artificially tailoring the gain spectrum of fibers. We present record-performance of such fibers and outline their future applications....

  4. Porous-core honeycomb bandgap THz fiber

    DEFF Research Database (Denmark)

    Nielsen, Kristian; Rasmussen, Henrik K.; Jepsen, Peter Uhd

    2011-01-01

    In this Letter we propose a novel (to our knowledge) porous-core honeycomb bandgap design. The holes of the porous core are the same size as the holes in the surrounding cladding, thereby giving the proposed fiber important manufacturing benefits. The fiber is shown to have a 0:35-THz......-wide fundamental bandgap centered at 1:05 THz. The calculated minimum loss of the fiber is 0:25 dB=cm....

  5. Main Factors for Affecting Photonic Bandgap of Photonic Crystals

    Institute of Scientific and Technical Information of China (English)

    LI Xia; XUE Wei; JIANG Yu-rong; YU Zhi-nong; WANG Hua-qing

    2007-01-01

    The factors affecting one dimensional (1D) and two dimensional (2D) photonic crystals (PhCs) are systemically analyzed in this paper by numerical simulation.Transfer matrix method (TMM) is employed for 1D PCs, both finite difference time domain method (FDTD) and plane wave expansion method (PWE) are employed for 2D PCs.The result shows that the photonic bandgaps (PBG) are directly affected by crystal type, crystal lattice constant, modulation of refractive index and periodicity, and it is should be useful for design of different type photonic crystals with the required PBG and functional devices.Finally, as an example, a near-IR 1D PCs narrow filter was designed.

  6. A three-dimensional tetrahedral-shaped conjugated small molecule for organic solar cells

    Directory of Open Access Journals (Sweden)

    QIN Yang

    2014-04-01

    Full Text Available We report the synthesis of a novel three-dimensional tetrahedral-shaped small molecule,SO,containing a tetraphenylsilane core and cyanoester functionalized terthiophene arms.A deep lying HOMO energy level of -5.3 eV and a narrow bandgap of 1.9 eV were obtained from cyclic voltammetry measurements.Absorption,X-ray scattering and differential scanning calorimetry experiments all indicate high crystallinity of this compound.Solar cells employing SO were fabricated and evaluated.The relatively low performance was mainly ascribed to lack of appreciable phase separation,which is confirmed by optical microscopy.

  7. Narrow with tunable optical band gap of CdS based core shell nanoparticles: Applications in pollutant degradation and solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Murugadoss, G., E-mail: murugadoss_g@yahoo.com [Department of Electric Engineering and Computer Science, School of Engineering, University of Hyogo, 2167 Shosha, Himeji, Hypogo 671-2280 (Japan); Thangamuthu, R. [Electrochemical Materials Science Division, CSIR-Central Electrochemical Research Institute, Karaikudi 630006, Tamilnadu (India); Jayavel, R. [Centre for Nanoscience and Technology, Anna University, Chennai 600025, Tamilnadu (India); Rajesh Kumar, M. [Department of Physics, Annamalai University, Annamalai nagar 608 002, Tamilnadu (India)

    2015-09-15

    In this work, sulfide-based core–shell heterostructures were successfully synthesized by chemical method. Structural, morphological, chemical composition, optical, and thermal properties of core–shell materials were investigated using different analytical techniques. The thickness of the shell can be tuned by controlling the concentration of respective shell precursors. TEM and HR-TEM analyses show that the particles are spherical in shape with particle size in the range 3–5 nm. Optical studies reveal that the core–shell materials possess strong visible-light photocatalytic activity. Among the four photocatalysts, CdS/SnS showed the best activity towards photo-degradation of methylene blue (MB). Addition of shells to the CdS core has a clear impact on the performance of solar cells. - Highlights: • Sulfide based core shell nanoparticles were synthesized by chemical method. • Structural, morphological and optical properties were studied. • Strong photocatalytic samples showed week photovoltaic performance.

  8. CNTs-Modified Nb3O7F Hybrid Nanocrystal towards Faster Carrier Migration, Lower Bandgap and Higher Photocatalytic Activity

    Science.gov (United States)

    Huang, Fei; Li, Zhen; Yan, Aihua; Zhao, Hui; Liang, Huagen; Gao, Qingyu; Qiang, Yinghuai

    2017-01-01

    Novel semiconductor photocatalysts have been the research focus and received much attention in recent years. The key issues for novel semiconductor photocatalysts are to effectively harvest solar energy and enhance the separation efficiency of the electron-hole pairs. In this work, novel Nb3O7F/CNTs hybrid nanocomposites with enhanced photocatalytic activity have been successfully synthesized by a facile hydrothermal plus etching technique. The important finding is that appropriate pH values lead to the formation of Nb3O7F nanocrystal directly. A general strategy to introdue interaction between Nb3O7F and CNTs markedly enhances the photocatalytic activity of Nb3O7F. Comparatively, Nb3O7F/CNTs nanocomposites exhibit higher photodegradation efficiency and faster photodegradation rate in the solution of methylene blue (MB) under visible-light irradiation. The higher photocatalytic activity may be attributed to more exposed active sites, higher carrier migration and narrower bandgap because of good synergistic effect. The results here may inspire more engineering, new design and facile fabrication of novel photocatalysts with highly photocatalytic activity.

  9. Characterization of Narrow Band-gap Polymers Based on thiophene-phenylene-thiophene for Photovolatic Cells%用于太阳能电池的(噻吩-苯-噻吩)基窄带隙聚合物的性能研究

    Institute of Scientific and Technical Information of China (English)

    苏雪花; 李薇; 王守伟

    2014-01-01

    采用Stilling偶合反应合成了噻吩-苯-噻吩和2,5-二(三甲基锡)基噻并[3,2-b]噻吩窄带隙交替共轭聚合物PTPT-bT(Eg=2.03eV)。所得聚合物具有良好的热稳定性、溶解性及成膜性能。共聚物在四氢呋喃中和固体薄膜中的光致发光发射峰分别为566 nm和583nm。最高占有分子轨道(HOMO)和最低未占有分子轨道(LUMO)值分别为-5.29eV和-3.01eV。在模拟太阳光照AM1.5(89mW· cm-2)下,基于PTPT-bT:PC70 BM(1:4)共混膜的光伏器件的光电转换效率(PCE)为2.99%,开路电压(Voc)为0.80V,短路电流(Jsc)为6.97mA/cm2,填充因子为0.48。%The alternating narrow band -gap conjugated polymer PTPT -bT (Eg =2.03eV) is synthesized, which derived from thiophene -phenylene-thiophene and 2, 5-bis (trimethylstannyl) thieno[3,2-b] thionphene by Stilling coupling reaction .In THF solution and solid thin film , PL emission peaks of the copolymer are around 566nm and 583nm respectively.The values of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) are -5.29eV and -3.01eV respectively.Under AM 1.5 simulator (89mW· cm-2), the photovotaic devices based on PTPT -bT:PC70 BM(1:2) blend ITO/PEDOT:PSS/PTPT-bT:PC70 BM/Ba/Al show power conversion efficiency (PCE) of 2.99%, an open circuit voltage(Voc) of 0.80 V, a short circuit cur-rent (Isc) of 6.97mA/cm2 and a fill factor (FF) of 48%.

  10. Microfabricated bulk wave acoustic bandgap device

    Science.gov (United States)

    Olsson, Roy H.; El-Kady, Ihab F.; McCormick, Frederick; Fleming, James G.; Fleming, Carol

    2010-06-08

    A microfabricated bulk wave acoustic bandgap device comprises a periodic two-dimensional array of scatterers embedded within the matrix material membrane, wherein the scatterer material has a density and/or elastic constant that is different than the matrix material and wherein the periodicity of the array causes destructive interference of the acoustic wave within an acoustic bandgap. The membrane can be suspended above a substrate by an air or vacuum gap to provide acoustic isolation from the substrate. The device can be fabricated using microelectromechanical systems (MEMS) technologies. Such microfabricated bulk wave phononic bandgap devices are useful for acoustic isolation in the ultrasonic, VHF, or UHF regime (i.e., frequencies of order 1 MHz to 10 GHz and higher, and lattice constants of order 100 .mu.m or less).

  11. A Strategy to Achieve High-Efficiency Organolead Trihalide Perovskite Solar Cells

    Science.gov (United States)

    Andalibi, Shabnam; Rostami, Ali; Darvish, Ghafar; Moravvej-Farshi, Mohammad Kazem

    2016-11-01

    Recent theoretical and experimental reports have shown that organometal lead halide perovskite solar cells have attracted attention as a low-cost photovoltaic technology offering high power conversion efficiency. However, the photovoltaic efficiency of these materials is still limited by poor chemical and structural stability in the case of methylammonium lead triiodide and by large bandgap in the case of methylammonium lead tribromide or trichloride. To obtain high-performance devices, we have investigated the computationally optimal efficiency for these materials using the detailed-balance method and present optimal intermediate-band perovskite solar cells with high open-circuit voltage. We model different halide perovskites using density function theory calculations and study their bandgap and absorption coefficient. Based on calculation results, surprisingly Hg doping in different halide perovskites introduces a narrow partially filled intermediate band in the forbidden bandgap. We investigate electrical and optical properties of MAPb0.97Hg0.03I3, MAPb0.96Hg0.04Br3, and MAPb0.96Hg0.04Cl3 and calculate the high absorption efficiency of the different perovskite structures to create thin films suitable for photovoltaic devices.

  12. Modeling of realistic cladding structures for photonic bandgap fibers

    DEFF Research Database (Denmark)

    Mortensen, Niels Asger; Nielsen, Martin Dybendal

    2004-01-01

    . For the fundamental bandgap we find that the bandgap edges (the intersections with the air line) shift toward shorter wavelengths when the air-filling fraction f is increased. The bandgap also broadens, and the relative bandwidth increases exponentially with f2. Compared with recent experiments [Nature 424, 657 (2003...

  13. Development of wider bandgap n-type a-SiOx:H and μc-SiOx:H as both doped and intermediate reflecting layer for a-Si:H/ a-Si1-xGex:H tandem solar cells

    Science.gov (United States)

    Chen, Po-Wei; Chen, Pei-Ling; Tsai, Chuang-Chuang

    2016-07-01

    In this work, we developed a-SiOx:H(n) and μc-SiOx:H(n) films as n-type layer, intermediate reflecting layer (IRL), and back-reflecting layer (BRL) to improve the light management in silicon thin-film solar cells. In the development of SiOx:H films, by properly adjusting the oxygen content of the films, the optical bandgap of μc-SiOx:H(n) can be increased while maintaining sufficient conductivity. Similar effect was found for a-SiOx:H(n). In a-Si:H single-junction cells, employing a-SiOx:H(n) as the replacement for a-Si:H(n) resulted in a relative efficiency enhancement of 11.4% due to the reduced parasitic absorption loss. We have also found that μc-SiOx:H(n) can replace back ITO layer as BRL, leading to a relative efficiency gain of 7.6%. For a-Si:H/ a-Si1- x Ge x:H tandem cell, employing μc-SiOx:H(n) as IRL increased the current density of top cell. In addition, employing a-SiOx:H(n) as a replacement of a-Si:H(n) in the top cell increased the current density of bottom cell due to the reduction of absorption loss. Combining all the improvements, the a-Si:H/ a-Si1-xGex:H tandem cell with efficiency of 9.2%, V OC = 1.58 V, J SC = 8.43 mA/cm2, and FF = 68.4% was obtained. [Figure not available: see fulltext.

  14. High efficiency thin film CdTe and a-Si based solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Compaan, A. D.; Deng, X.; Bohn, R. G.

    2000-01-04

    This report describes work done by the University of Toledo during the first year of this subcontract. During this time, the CdTe group constructed a second dual magnetron sputter deposition facility; optimized reactive sputtering for ZnTe:N films to achieve 10 ohm-cm resistivity and {approximately}9% efficiency cells with a copper-free ZnTe:N/Ni contact; identified Cu-related photoluminescence features and studied their correlation with cell performance including their dependence on temperature and E-fields; studied band-tail absorption in CdS{sub x}Te{sub 1{minus}x} films at 10 K and 300 K; collaborated with the National CdTe PV Team on (1) studies of high-resistivity tin oxide (HRT) layers from ITN Energy Systems, (2) fabrication of cells on the HRT layers with 0, 300, and 800-nm CdS, and (3) preparation of ZnTe:N-based contacts on First Solar materials for stress testing; and collaborated with Brooklyn College for ellipsometry studies of CdS{sub x}Te{sub 1{minus}x} alloy films, and with the University of Buffalo/Brookhaven NSLS for synchrotron X-ray fluorescence studies of interdiffusion in CdS/CdTe bilayers. The a-Si group established a baseline for fabricating a-Si-based solar cells with single, tandem, and triple-junction structures; fabricated a-Si/a-SiGe/a-SiGe triple-junction solar cells with an initial efficiency of 9.7% during the second quarter, and 10.6% during the fourth quarter (after 1166 hours of light-soaking under 1-sun light intensity at 50 C, the 10.6% solar cells stabilized at about 9%); fabricated wide-bandgap a-Si top cells, the highest Voc achieved for the single-junction top cell was 1.02 V, and top cells with high FF (up to 74%) were fabricated routinely; fabricated high-quality narrow-bandgap a-SiGe solar cells with 8.3% efficiency; found that bandgap-graded buffer layers improve the performance (Voc and FF) of the narrow-bandgap a-SiGe bottom cells; and found that a small amount of oxygen partial pressure ({approximately}2 {times} 10

  15. Origin of unusual bandgap shift and dual emission in organic-inorganic lead halide perovskites.

    Science.gov (United States)

    Dar, M Ibrahim; Jacopin, Gwénolé; Meloni, Simone; Mattoni, Alessandro; Arora, Neha; Boziki, Ariadni; Zakeeruddin, Shaik Mohammed; Rothlisberger, Ursula; Grätzel, Michael

    2016-10-01

    Emission characteristics of metal halide perovskites play a key role in the current widespread investigations into their potential uses in optoelectronics and photonics. However, a fundamental understanding of the molecular origin of the unusual blueshift of the bandgap and dual emission in perovskites is still lacking. In this direction, we investigated the extraordinary photoluminescence behavior of three representatives of this important class of photonic materials, that is, CH3NH3PbI3, CH3NH3PbBr3, and CH(NH2)2PbBr3, which emerged from our thorough studies of the effects of temperature on their bandgap and emission decay dynamics using time-integrated and time-resolved photoluminescence spectroscopy. The low-temperature (perovskite composition, the bandgap exhibits an unusual blueshift by raising the temperature from 15 to 300 K. Density functional theory and classical molecular dynamics simulations allow for assigning the additional photoluminescence peak to the presence of molecularly disordered orthorhombic domains and also rationalize that the unusual blueshift of the bandgap with increasing temperature is due to the stabilization of the valence band maximum. Our findings provide new insights into the salient emission properties of perovskite materials, which define their performance in solar cells and light-emitting devices.

  16. Jihadism, Narrow and Wide

    DEFF Research Database (Denmark)

    Sedgwick, Mark

    2015-01-01

    The term “jihadism” is popular, but difficult. It has narrow senses, which are generally valuable, and wide senses, which may be misleading. This article looks at the derivation and use of “jihadism” and of related terms, at definitions provided by a number of leading scholars, and at media usage....... It distinguishes two main groups of scholarly definitions, some careful and narrow, and some appearing to match loose media usage. However, it shows that even these scholarly definitions actually make important distinctions between jihadism and associated political and theological ideology. The article closes...

  17. Bandgap Narrowing of Titanium Dioxide by Iron Doping for Enhanced Photocatalytic Performance of Nanohybrids with CNTs

    Science.gov (United States)

    Khang, Nguyen Cao; Thanh, Do Minh; Van Minh, Nguyen

    2016-10-01

    Fe-doped TiO2/carbon nanotube (CNT) nanohybrids have been synthesized by a hydrolysis method. The samples were characterized by scanning electron microscopy, high-resolution transmission electron microscopy (HR-TEM), x-ray diffraction analysis, and ultraviolet-visible (UV-Vis) optical absorption spectroscopy. HR-TEM reveals Fe-doped TiO2 nanoparticles of about 8 nm in size attached to CNT sidewalls. Compared with TiO2, the UV-Vis spectra of all the nanohybrid materials exhibited red-shift with increased absorbance in the visible range. The photocatalytic performance was tested by photocatalytic degradation of methylene blue (MB) and methylene orange (MO) under visible-light irradiation. The results suggest that Fe-doped TiO2/CNT nanohybrid catalysts exhibit much higher dye degradation activity compared with neat TiO2, with the highest activity being observed for 6% Fe-doped TiO2. The experimental results were combined with density functional theory calculations of electronic band structure and density of states to understand the bonding states between TiO2 and CNTs, proving that the TiO2/CNT system is stable.

  18. Monte Carlo analysis of Gunn oscillations in narrow and wide band-gap asymmetric nanodiodes

    Science.gov (United States)

    González, T.; Iñiguez-de-la Torre, I.; Pardo, D.; Mateos, J.; Song, A. M.

    2009-11-01

    By means of Monte Carlo simulations we show the feasibility of asymmetric nonlinear planar nanodiodes for the development of Gunn oscillations. For channel lengths about 1 μm, oscillation frequencies around 100 GHz are predicted in InGaAs diodes, being significantly higher, around 400 GHz, in the case of GaN structures. The DC to AC conversion efficiency is found to be higher than 1% for the fundamental and second harmonic frequencies in GaN diodes.

  19. Correlates of Narrow Bracketing

    DEFF Research Database (Denmark)

    Koch, Alexander; Nafziger, Julia

    We examine whether different phenomena of narrow bracketing can be traced back to some common characteristic and whether and how different phenomena are related. We find that making dominated lottery choices or ignoring the endowment when making risky choices are related phenomena and are both as...

  20. Advances in photonic bandgap fiber functionality

    DEFF Research Database (Denmark)

    Lyngsøe, Jens Kristian

    In order to take advantage of the many intriguing optical properties of photonic bandgap fibers, there are some technological challenges that have to be addressed. Among other things this includes transmission loss and the fibers ability to maintain field polarization. The work presented...... in this thesis addresses these two fundamental properties in both hollow core photonic crystal fibers and solid photonic bandgap fibers. Transmission loss in hollow core photonic crystal fibers is dominated by light scattering at the silica surfaces inside the fiber. In the current work it has been...... experimentally demonstrated that the minimum loss wavelength is located in the spectral region around 2000 nm, where the transmission loss in these fibers is significantly lower than in conventional solid silica fibers. Additionally it has been shown that transmission loss can be lowered roughly 40...

  1. Liquid Crystal photonic Bandgap Fiber Devices

    DEFF Research Database (Denmark)

    Wei, Lei

    In this Ph.D. thesis, an experimental investigation of liquid crystal photonic bandgap (LCPBG) fiber devices and applications is presented. Photonic crystal fibers (PCFs) consist of a cladding microstructure with periodic index variations and a core defined by a defect of the structure....... The presence of liquid crystals (LCs) in the air-holes of the PCF transforms the fiber from a total internal reflection (TIR) guiding type into a photonic bandgap (PBG) guiding type. The light is confined to the silica core by coherent scattering from the LC-filled air-holes and the transmission spectrum...... of each LCPBG fiber. Finally, the applications for LCPBG fiber devices based on the on-chip platform design have been demonstrated in realizing microwave true-time delay and creating an electrically tunable fiber laser. Referatet mailes...

  2. Liquid Crystal photonic Bandgap Fiber Devices

    DEFF Research Database (Denmark)

    Wei, Lei

    In this Ph.D. thesis, an experimental investigation of liquid crystal photonic bandgap (LCPBG) fiber devices and applications is presented. Photonic crystal fibers (PCFs) consist of a cladding microstructure with periodic index variations and a core defined by a defect of the structure....... The presence of liquid crystals (LCs) in the air-holes of the PCF transforms the fiber from a total internal reflection (TIR) guiding type into a photonic bandgap (PBG) guiding type. The light is confined to the silica core by coherent scattering from the LC-filled air-holes and the transmission spectrum...... of each LCPBG fiber. Finally, the applications for LCPBG fiber devices based on the on-chip platform design have been demonstrated in realizing microwave true-time delay and creating an electrically tunable fiber laser. Referatet mailes...

  3. Oscillatory quantum interference effects in narrow-gap semiconductor heterostructures

    Science.gov (United States)

    Lillianfeld, R. B.; Kallaher, R. L.; Heremans, J. J.; Chen, Hong; Goel, N.; Chung, S. J.; Santos, M. B.; Van Roy, W.; Borghs, G.

    2010-01-01

    We investigate quantum interference phenomena in narrow bandgap semiconductors under strong spin-orbit interaction, by measuring the magnetoresistance across mesoscopic closed-path structures fabricated in two-dimensional electron systems. We discuss our results in terms of four quantum interference effects brought about by geometric phases acquired by the electron wave functions: the Aharonov-Bohm phase, the Altshuler-Aronov-Spivak effect, the Berry's phase due to the evolution of the spin degree of freedom, and the Aharonov-Casher phase.

  4. Two-dimensional Kagome photonic bandgap waveguide

    DEFF Research Database (Denmark)

    Nielsen, Jens Bo; Søndergaard, Thomas; Libori, Stig E. Barkou;

    2000-01-01

    The transverse-magnetic photonic-bandgap-guidance properties are investigated for a planar two-dimensional (2-D) Kagome waveguide configuration using a full-vectorial plane-wave-expansion method. Single-moded well-localized low-index guided modes are found. The localization of the optical modes...... is investigated with respect to the width of the 2-D Kagome waveguide, and the number of modes existing for specific frequencies and waveguide widths is mapped out....

  5. Wide bandgap matrix switcher, amplifier and oscillator

    Energy Technology Data Exchange (ETDEWEB)

    Sampayan, Stephen

    2016-08-16

    An electronic device comprising an optical gate, an electrical input an electrical output and a wide bandgap material positioned between the electrical input and the electrical output to control an amount of current flowing between the electrical input and the electrical output in response to a stimulus received at the optical gate can be used in wideband telecommunication applications in transmission of multi-channel signals.

  6. Temperature and magnetization-dependent band-gap renormalization and optical many-body effects in diluted magnetic semiconductors

    OpenAIRE

    2005-01-01

    We calculate the Coulomb interaction induced density, temperature and magnetization dependent many-body band-gap renormalization in a typical diluted magnetic semiconductor GaMnAs in the optimally-doped metallic regime as a function of carrier density and temperature. We find a large (about 0.1 eV) band gap renormalization which is enhanced by the ferromagnetic transition. We also calculate the impurity scattering effect on the gap narrowing. We suggest that the temperature, magnetization, an...

  7. A new photonic bandgap cover for a patch antenna with a photonic bandgap substrate

    Institute of Scientific and Technical Information of China (English)

    林青春; 朱方明; 何赛灵

    2004-01-01

    A new photonic bandgap (PBG) cover for a patch antenna with a photonic bandgap substrate is introduced. The plane wave expansion method and the FDTD method were used to calculate such an antenna system. Numerical results for the input return loss, radiation pattern, surface wave, and the directivity of the antennas are presented. A comparison between the conventional patch antenna and the new PBG antenna is given. It is shown that the new PBG cover is very efficient for improving the radiation directivity. The physical reasons for the improvement are also given.

  8. Fluorene-based narrow-band-gap copolymers for red light- emitting diodes and bulk heterojunction photovoltaic cells

    Institute of Scientific and Technical Information of China (English)

    Mingliang SUN; Li WANG; Yangjun XIA; Bin DU; Ransheng LIU; Yong CAO

    2008-01-01

    A series of narrow band-gap conjugated copo-lymers (PFO-DDQ) derived from 9,9-dioctylfluorene (DOF) and 2,3-dimethyl-5,8-dithien-2-yl-quinoxalines (DDQ) is prepaid by the palladium-catalyzed Suzuki coupling reaction with the molar feed ratio of DDQ at around 1%,5%,15%,30% and 50%,respectively.The obtained polymers are readily soluble in common organic solvents.The solutions and the thin solid films of the copolymers absorb light from 300-590 nm with two absorbance.peaks at around 380 and 490 nm.The intens-ity of 490 nm peak increases with the increasing DDQ content in the polymers.Efficient energy transfer due to exciton trapping on narrow-band-gap DDQ sites has been observed.The PL emission consists exclusively of DDQ unit emission at around 591 643 nm depending on the DDQ content in solid film.The EL emission peaks are red-shifted from 580 nm for PFO-DDQ1 to 635 nm for PFO-DDQ50.The highest external quantum efficiency achieved with the device configuration ITO/PEDOT/ PVK/PFO-DDQt5/Ba/A1 is 1.33% with a luminous effi-ciency 1.54 cd/A.Bulk heterojunction photovoltaic cells fabricated from composite films of PFO-DDQ30 copoly-mer and [6,6]-phenyl C61 butyric acid methyl ester (PCBM) as electron donor and electron acceptor,respect-ively in device configuration:ITO/PEDOT:PSS/PFO-DDQ30:PCBM/PFPNBr/Al shows power conversion effi-ciencies of 1.18% with open-circuit voltage (Voc) of 0.90 V and short-circuit current density (Jsc) of 2.66 mA/cm2 under an AM1.5 solar simulator (100 mW/cm2).The photocurrent response wavelengths of the PVCs based on PFO-DDQ30/PCBM blends covers 300-700 nm.This indicates that these kinds of low band-gap polymers are promising candidates for polymeric solar cells and red light-emitting diodes.

  9. Heavily doped transparent-emitter regions in junction solar cells, diodes, and transistors

    Science.gov (United States)

    Shibib, M. A.; Lindholm, F. A.; Therez, F.

    1979-01-01

    The paper presents an analytical treatment of transparent-emitter devices, particularly solar cells, that is more complete than previously available treatments. The proposed approach includes the effects of bandgap narrowing, Fermi-Dirac statistics, built-in field due to impurity profile, and a finite surface recombination velocity at the emitter surface. It is demonstrated that the transparent-emitter model can predict experimental values of Voc observed on n(plus)-p thin diffused junction silicon solar cells made on low-resistivity (0.1 ohm-cm) substrates. A test is included for the self-consistent validity of the transparent-emitter model. This test compares the calculated transit time of minority carriers across the emitter with the Auger-impact minority-carrier lifetime within the emitter region.

  10. Heavily doped transparent-emitter regions in junction solar cells, diodes, and transistors

    Science.gov (United States)

    Shibib, M. A.; Lindholm, F. A.; Therez, F.

    1979-01-01

    The paper presents an analytical treatment of transparent-emitter devices, particularly solar cells, that is more complete than previously available treatments. The proposed approach includes the effects of bandgap narrowing, Fermi-Dirac statistics, built-in field due to impurity profile, and a finite surface recombination velocity at the emitter surface. It is demonstrated that the transparent-emitter model can predict experimental values of Voc observed on n(plus)-p thin diffused junction silicon solar cells made on low-resistivity (0.1 ohm-cm) substrates. A test is included for the self-consistent validity of the transparent-emitter model. This test compares the calculated transit time of minority carriers across the emitter with the Auger-impact minority-carrier lifetime within the emitter region.

  11. Determination of size and bandgap distributions of Si nanoparticles from photoluminescence excitation and emission spectra in n-type stain etched porous silicon

    Energy Technology Data Exchange (ETDEWEB)

    Rustamov, F.A., E-mail: farhad.rustamov@bsu.az; Darvishov, N.H.; Bagiev, V.E.; Mamedov, M.Z.; Bobrova, E.Y.; Qafarova, H.O.

    2014-10-15

    The photoluminescence excitation and emission spectra of n-type stain etched porous silicon layers were investigated. From these spectra the average values of optical bandgap and photoluminescence peak position were determined. Based on these experimental data, the photoluminescence emission spectra of porous silicon were analyzed by the phenomenological theory and the fitting parameters of the theory were defined. The size and bandgap distributions of silicon nanoparticles were determined and their mean values were calculated. It was found that the investigated PS samples are the ensemble of nanoparticles with size between 1.5 nm and 2.8 nm and a bandgap from 2 eV to 3.2 eV distributed with different probabilities depending on the formation time of porous silicon. It is shown that with increasing formation time, the average size of nanocrystals is slightly increasing, while the average bandgap is slightly narrowing. - Highlights: • Stain etched n-type porous silicon layers were formed in modified solution. • Joint theoretical analysis of excitation and emission spectra was performed. • Size and bandgap distributions of nanocrystals were determined. • Mean values of nanocrystal size and bandgap were determined.

  12. INVESTIGATION ON EMI EFFECTS IN BANDGAP VOLTAGE REFERENCES

    OpenAIRE

    Fiori, Franco; Crovetti S., Paolo

    2002-01-01

    International audience; In this paper the susceptibility of integrated bandgap voltage references to Electromagnetic Interference (EMI) is investigated by on-chip measurements carried out on Kuijk and Tsividis bandgap circuits. These measurements highlight the offset in the reference voltage induced by continuous wave (CW) EMI and the complete failures which may be experienced by bandgap circuits. The role of the susceptibility of the startup circuit and of the operational amplifier which are...

  13. Polarizing 50micrometers Core Yb-Doped Photonic Bandgap Fiber

    Science.gov (United States)

    2015-02-08

    properly. Recent reports demonstrate that the birefringence in photonic bandgap fibers (PBFs) can provide single-polarization operation by shifting the...add ref]. Here, we demonstrate a 50µm core Yb-doped polarizing photonic bandgap fiber (PBF) for single-polarization operation 1. REPORT DATE (DD-MM...19-08-2015 Approved for public release; distribution is unlimited. Polarizing 50µm core Yb-doped photonic bandgap fiber The views, opinions and/or

  14. Band gap narrowing models tested on low recombination phosphorus laser doped silicon

    Science.gov (United States)

    Dahlinger, Morris; Carstens, Kai

    2016-10-01

    This manuscript discusses bandgap narrowing models for highly phosphorus doped silicon. We simulate the recombination current pre-factor J0,phos in PC1Dmod 6.2 of measured doping profiles and apply the theoretical band gap narrowing model of Schenk [J. Appl. Phys. 84, 3684 (1998)] and an empirical band gap narrowing model of Yan and Cuevas [J. Appl. Phys. 114, 044508 (2013)]. The recombination current pre-factor of unpassivated and passivated samples measured by the photo conductance measurement and simulated J0,phos agrees well, when the band gap narrowing model of Yan and Cuevas is applied. With the band gap narrowing model of Schenk, the simulation cannot reproduce the measured J0,phos. Furthermore, the recombination current pre-factor of our phosphorus laser doped silicon samples are comparable with furnace diffused samples. There is no indication of recombination active defects, thus no laser induced defects in the diffused volume.

  15. Air-guiding Photonic Bandgap Fibers

    DEFF Research Database (Denmark)

    Hansen, Theis Peter

    2005-01-01

    Photonic bandgap fibers that guide light in an air core have attracted much interest since their first demonstration in 1999. The prospect of low-loss guiding of light in air has importance for a multitude of applications, such as data transmission, gas sensors, dispersion compensation and guiding...... of high-power pulses. The low overlap between light and glass affects both the loss and nonlinear properties of the fiber. At the same time, the strong overlap between light and air provides a mean for creating convenient gas-filled devices with extremely long interaction lengths. In this project...

  16. Development of High Efficiency, Stacked Multiple Bandgap Solar Cells.

    Science.gov (United States)

    1982-09-01

    calculated spectral responses and experiental measurements for top cells. 154 Reasonably good agreement between theory and experiment is seen f or the...2.52 S. Mukai, 1. Makita, and S. Gonda, J. Appl. Phys., 50, 1979, p. 1304. 2.53 C. Flores and D. Passoni (private communication ). 2.54 A. S. Jordan, J

  17. Contact and Bandgap Engineering in Two Dimensional Crystal

    Science.gov (United States)

    Chu, Tao

    At the heart of semiconductor research, bandgap is one of the key parameters for materials and determine their applications in modern technologies. For traditional bulk semiconductors, the bandgap is determined by the chemical composition and specific arrangement of the crystal lattices, and usually invariant during the device operation. Nevertheless, it is highly desirable for many optoelectronic and electronic applications to have materials with continuously tunable bandgap available. In the past decade, 2D layered materials including graphene and transition metal dichalcogenides (TMDs) have sparked interest in the scientific community, owing to their unique material properties and tremendous potential in various applications. Among many newly discovered properties that are non-existent in bulk materials, the strong in-plane bonding and weak van der Waals inter-planar interaction in these 2D layered structures leads to a widely tunable bandgap by electric field. This provides an extra knob to engineer the fundamental material properties and open a new design space for novel device operation. This thesis focuses on this field controlled dynamic bandgap and can be divided into three parts: (1) bilayer graphene is the first known 2D crystal with a bandgap can be continuously tuned by electric field. However, the electrical transport bandgaps is much smaller than both theoretical predictions and extracted bandgaps from optical measurements. In the first part of the thesis, the limiting factors of preventing achieving a large transport bandgap in bilayer graphene are investigated and different strategies to achieve a large transport bandgap are discussed, including the vertically scaling of gate oxide and patterning channel into ribbon structure. With a record large transport bandgap of ~200meV, a dual-gated semiconducting bilayer graphene P/N junction with extremely scaled gap of 20nm in-between is fabricated. A tunable local maxima feature, associated with 1D v

  18. Voc Degradation in TF-VLS Grown InP Solar Cells

    Energy Technology Data Exchange (ETDEWEB)

    Sun, Yubo; Sun, Xingshu; Johnston, Steve; Sutter-Fella, Carolin M.; Hettick, Mark; Javey, Ali; Bermel, Peter

    2016-11-21

    Here we consider two hypotheses to explain the open-circuit voltage (VOC) degradation observed in thin-film vapor-liquid-solid (TF-VLS) grown p-type InP photovoltaic cells: bandgap narrowing and local shunting. First, a bandgap (Eg) narrowing effect is hypothesized, based on the surface inhomogeneity of VLS InP captured by the photoluminescence (PL) image. The PL data was used to estimate a spatially-resolved active VOC across surface of the InP sample. Combining this data with the effective Jsc allowed an assessment of the I-V characteristics of individual unit cells. Next, an H-SPICE diode compact model was utilized to reproduce the I-V characteristics of the whole sample. We find a good fit to the I-V performance of TF-VLS grown InP solar cell. Second, a local shunting effect was also considered as an alternative explanation of the VOC degradation effect. Again, PL image data was used, and small local shunt resistance was added in arbitrary elementary unit cells to represent certain dark spots seen in the PL image and dictate the VOC degradation occurred in the sample.

  19. Computation with narrow CTCs

    CERN Document Server

    Say, A C Cem

    2011-01-01

    We examine some variants of computation with closed timelike curves (CTCs), where various restrictions are imposed on the memory of the computer, and the information carrying capacity and range of the CTC. We give full characterizations of the classes of languages recognized by polynomial time probabilistic and quantum computers that can send a single classical bit to their own past. Such narrow CTCs are demonstrated to add the power of limited nondeterminism to deterministic computers, and lead to exponential speedup in constant-space probabilistic and quantum computation. We show that, given a time machine with constant negative delay, one can implement CTC-based computations without the need to know about the runtime beforehand.

  20. Direct-indirect character of the bandgap in methylammonium lead iodide perovskite

    Science.gov (United States)

    Hutter, Eline M.; Gélvez-Rueda, María C.; Osherov, Anna; Bulović, Vladimir; Grozema, Ferdinand C.; Stranks, Samuel D.; Savenije, Tom J.

    2017-01-01

    Metal halide perovskites such as methylammonium lead iodide (CH3NH3PbI3) are generating great excitement due to their outstanding optoelectronic properties, which lend them to application in high-efficiency solar cells and light-emission devices. However, there is currently debate over what drives the second-order electron-hole recombination in these materials. Here, we propose that the bandgap in CH3NH3PbI3 has a direct-indirect character. Time-resolved photo-conductance measurements show that generation of free mobile charges is maximized for excitation energies just above the indirect bandgap. Furthermore, we find that second-order electron-hole recombination of photo-excited charges is retarded at lower temperature. These observations are consistent with a slow phonon-assisted recombination pathway via the indirect bandgap. Interestingly, in the low-temperature orthorhombic phase, fast quenching of mobile charges occurs independent of the temperature and photon excitation energy. Our work provides a new framework to understand the optoelectronic properties of metal halide perovskites and analyse spectroscopic data.

  1. Gas sensing using air-guiding photonic bandgap fibers

    DEFF Research Database (Denmark)

    Ritar, Tuomo; Tuominen, J.; Ludvigsen, Hanne

    2004-01-01

    We demonstrate the high sensitivity of gas sensing using a novel air-guiding photonic bandgap fiber. The bandgap fiber is spliced to a standard single-mode fiber at the input end for easy coupling and filled with gas through the other end placed in a vacuum chamber. The technique is applied...

  2. Electrically tunable liquid crystal photonic bandgap fiber laser

    DEFF Research Database (Denmark)

    Olausson, Christina Bjarnal Thulin; Scolari, Lara; Wei, Lei;

    2010-01-01

    We demonstrate electrical tunability of a fiber laser by using a liquid crystal photonic bandgap fiber. Tuning of the laser is achieved by combining the wavelength filtering effect of a liquid crystal photonic bandgap fiber device with an ytterbium-doped photonic crystal fiber. We fabricate an al...

  3. Review of wide band-gap semiconductors technology

    Directory of Open Access Journals (Sweden)

    Jin Haiwei

    2016-01-01

    Full Text Available Silicon carbide (SiC and gallium nitride (GaN are typical representative of the wide band-gap semiconductor material, which is also known as third-generation semiconductor materials. Compared with the conventional semiconductor silicon (Si or gallium arsenide (GaAs, wide band-gap semiconductor has the wide band gap, high saturated drift velocity, high critical breakdown field and other advantages; it is a highly desirable semiconductor material applied under the case of high-power, high-temperature, high-frequency, anti-radiation environment. These advantages of wide band-gap devices make them a hot spot of semiconductor technology research in various countries. This article describes the research agenda of United States and European in this area, focusing on the recent developments of the wide band-gap technology in the US and Europe, summed up the facing challenge of the wide band-gap technology.

  4. Quaternary alloy semiconductor nanobelts with bandgap spanning the entire visible spectrum.

    Science.gov (United States)

    Pan, Anlian; Liu, Ruibin; Sun, Minghua; Ning, Cun-Zheng

    2009-07-15

    We used an improved cothermal evaporation route for the first time to achieve quaternary semiconductor nanostructured alloys, using an example of Zn(x)Cd(1-x)S(y)Se(1-y) nanobelts. The PL (bandgap) of these as-grown nanostructured alloys can be continuously tunable across the entire visible spectrum through experimentally controlling their compositions. Such widely controlled alloy nanostructures via composition/light emission provide a new material platform for applications in wavelength-tunable lasers, multicolor detectors, full-spectrum solar cells, LEDs, and color displays.

  5. Supercritical synthesis and in situ deposition of PbS nanocrystals with oleic acid passivation for quantum dot solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Tavakoli, M.M. [Department of Materials Science and Engineering, Sharif University of Technology, 14588 Tehran (Iran, Islamic Republic of); Simchi, A., E-mail: simchi@sharif.edu [Department of Materials Science and Engineering, Sharif University of Technology, 14588 Tehran (Iran, Islamic Republic of); Institute for Nanoscience and Nanotechnology, Sharif University of Technology, 14588 Tehran (Iran, Islamic Republic of); Aashuri, H. [Department of Materials Science and Engineering, Sharif University of Technology, 14588 Tehran (Iran, Islamic Republic of)

    2015-04-15

    Colloidal quantum dot solar cells have recently attracted significant attention due to their low-processing cost and surging photovoltaic performance. In this paper, a novel, reproducible, and simple solution-based process based on supercritical fluid toluene is presented for in situ growth and deposition PbS nanocrystals with oleic-acid passivation. A lead precursor containing sulfur was mixed with oleic acid in toluene and processed in a supercritical fluid condition at different temperatures of 140, 270 and 330 °C for 20 min. The quantum dots were deposited on a fluorine-doped tin oxide glass substrate inside the supercritical reactor. Transmission electron microscopy, X-ray diffraction, absorption and dynamic light scattering showed that the nanocrystals processed at the supercritical condition (330 °C) are fully crystalline with a narrow size distribution of ∼3 nm with an absorption wavelength of 915 nm (bandgap of 1.3 eV). Fourier transform infrared spectroscopy indicated that the PbS quantum dots are passivated by oleic acid molecules during the growth. Photovoltaic characteristics of Schottky junction solar cells showed an improvement over devices prepared by spin-coating. - Highlights: • Supercritical fluid processing and in situ deposition of PbS QDs are presented. • The prepared nanocrystals are mono-dispersed with an optical bandgap of 1.3 eV. • Photovoltaic performance of the in situ deposited nanocrystals is reported. • An improved PV performance compared to spin coated Schottky solar cells is shown.

  6. Study program to improve the open-circuit voltage of low resistivity single crystal silicon solar cells

    Science.gov (United States)

    Minnucci, J. A.; Matthei, K. W.

    1980-01-01

    The results of a 14 month program to improve the open circuit voltage of low resistivity silicon solar cells are described. The approach was based on ion implantation in 0.1- to 10.0-ohm-cm float-zone silicon. As a result of the contract effort, open circuit voltages as high as 645 mV (AMO 25 C) were attained by high dose phosphorus implantation followed by furnace annealing and simultaneous SiO2 growth. One key element was to investigate the effects of bandgap narrowing caused by high doping concentrations in the junction layer. Considerable effort was applied to optimization of implant parameters, selection of furnace annealing techniques, and utilization of pulsed electron beam annealing to minimize thermal process-induced defects in the completed solar cells.

  7. Liquid Crystals and Photonic Bandgap Fiber Components

    DEFF Research Database (Denmark)

    Weirich, Johannes; Wei, Lei; Scolari, Lara

    Liquid Crystal(LC)filled Photonic Crystal Fibers(PCFs) represent a promising platform for the design and the fabrication of tunable all-in fiber devices. Tunability is achieved by varying the refractive index of the LC thermally, optically or electrically. In this contribution we present important...... parts of the LC theory as well as an application of a LC infiltrated PCF subject to an external electrostatic field. The fiber is placed between two electrodes and the voltage is increased step by step leading to the reorientation of the LC in the fiber capillaries. This mechanism can be used to produce...... a swichable polarizer, and an on chip LC photonic bandgap fiber polarimeter is presented, which admits strong attenuation of one polarization direction while the other one is nearly unaffected....

  8. Quantum electrodynamics near a photonic bandgap

    Science.gov (United States)

    Liu, Yanbing; Houck, Andrew A.

    2017-01-01

    Photonic crystals are a powerful tool for the manipulation of optical dispersion and density of states, and have thus been used in applications from photon generation to quantum sensing with nitrogen vacancy centres and atoms. The unique control provided by these media makes them a beautiful, if unexplored, playground for strong-coupling quantum electrodynamics, where a single, highly nonlinear emitter hybridizes with the band structure of the crystal. Here we demonstrate that such a hybridization can create localized cavity modes that live within the photonic bandgap, whose localization and spectral properties we explore in detail. We then demonstrate that the coloured vacuum of the photonic crystal can be employed for efficient dissipative state preparation. This work opens exciting prospects for engineering long-range spin models in the circuit quantum electrodynamics architecture, as well as new opportunities for dissipative quantum state engineering.

  9. Novel 1-D Sandwich Photonic Bandgap Structure

    Institute of Scientific and Technical Information of China (English)

    庞云波; 高葆新

    2004-01-01

    A sandwich photonic bandgap (PBG) structure is a novel PBG structure whose periodic lattice is buried in the middle of a substrate. Neither drilling nor suspending the substrate is required, and the integrity of the ground plane is maintained. This paper presents several modification techniques for sandwich PBG structure fabrication. The forbidden gap can be improved by adopting the chirping technique, applying the tapering technique, enlarging the periodic elements, adjusting the location of the periodic lattice in the substrate, and using different dielectric media H-shape elements. A finite difference time domain method is applied to analyze the structures. Deep and wide stopbands can be obtained using the modified sandwich structures. Experimental measurement results agree well with the theoretical analysis.

  10. Bandgap engineering of GaN nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Ming, Bang-Ming; Yan, Hui [College of Materials Science and Engineering, Beijing University of Technology, Beijing 100124 (China); Wang, Ru-Zhi, E-mail: wrz@bjut.edu.cn, E-mail: yamcy@csrc.ac.cn [College of Materials Science and Engineering, Beijing University of Technology, Beijing 100124 (China); Beijing Computational Science Research Center, Beijing, 100094 (China); Yam, Chi-Yung, E-mail: wrz@bjut.edu.cn, E-mail: yamcy@csrc.ac.cn [Beijing Computational Science Research Center, Beijing, 100094 (China); Xu, Li-Chun [College of Physics and Optoelectronics, Taiyuan University of Technology, Taiyuan 030024 (China); Lau, Woon-Ming [Beijing Computational Science Research Center, Beijing, 100094 (China); Chengdu Green Energy and Green Manufacturing Technology R& D Center, Chengdu, Sichuan, 610207 (China)

    2016-05-15

    Bandgap engineering has been a powerful technique for manipulating the electronic and optical properties of semiconductors. In this work, a systematic investigation of the electronic properties of [0001] GaN nanowires was carried out using the density functional based tight-binding method (DFTB). We studied the effects of geometric structure and uniaxial strain on the electronic properties of GaN nanowires with diameters ranging from 0.8 to 10 nm. Our results show that the band gap of GaN nanowires depends linearly on both the surface to volume ratio (S/V) and tensile strain. The band gap of GaN nanowires increases linearly with S/V, while it decreases linearly with increasing tensile strain. These linear relationships provide an effect way in designing GaN nanowires for their applications in novel nano-devices.

  11. Jacquard-woven photonic bandgap fiber displays

    CERN Document Server

    Sayed, Imran; Skorobogatiy, Maksim

    2010-01-01

    We present an overview of photonic textile displays woven on a Jacquard loom, using newly discovered polymer photonic bandgap fibers that have the ability to change color and appearance when illuminated with ambient or transmitted light. The photonic fiber can be thin (smaller than 300 microns in diameter) and highly flexible, which makes it possible to weave in the weft on a computerized Jacquard loom and develop intricate double weave structures together with a secondary weft yarn. We demonstrate how photonic crystal fibers enable a variety of color and structural patterns on the textile, and how dynamic imagery can be created by balancing the ambient and emitted radiation. Finally, a possible application in security ware for low visibility conditions is described as an example.

  12. Photovoltaic efficiency of an indirect bandgap material

    Science.gov (United States)

    Tomasik, Michelle; Mangan, Niall; Grossman, Jeffrey

    2015-03-01

    Photovoltaic materials with direct band gap transitions absorb light more readily than those with indirect gaps, allowing for thinner devices. However, direct bands also suffer faster rates of radiative recombination than indirect bandgap materials. Some novel photovoltaic absorber materials, such as tin sulfide, have both direct and indirect gaps. Such materials raise the question of whether the multiple energy states benefit or harm device efficiency. We develop a model for current in a device with direct and indirect band gaps using detailed balance, similar to the Shockley-Quiesser model for direct band photovoltaics. We explore the effects of the following on device performance: transition probability of carriers between the direct and indirect state, and relative transport rate in each band.

  13. Narrow, duplicated internal auditory canal

    Energy Technology Data Exchange (ETDEWEB)

    Ferreira, T. [Servico de Neurorradiologia, Hospital Garcia de Orta, Avenida Torrado da Silva, 2801-951, Almada (Portugal); Shayestehfar, B. [Department of Radiology, UCLA Oliveview School of Medicine, Los Angeles, California (United States); Lufkin, R. [Department of Radiology, UCLA School of Medicine, Los Angeles, California (United States)

    2003-05-01

    A narrow internal auditory canal (IAC) constitutes a relative contraindication to cochlear implantation because it is associated with aplasia or hypoplasia of the vestibulocochlear nerve or its cochlear branch. We report an unusual case of a narrow, duplicated IAC, divided by a bony septum into a superior relatively large portion and an inferior stenotic portion, in which we could identify only the facial nerve. This case adds support to the association between a narrow IAC and aplasia or hypoplasia of the vestibulocochlear nerve. The normal facial nerve argues against the hypothesis that the narrow IAC is the result of a primary bony defect which inhibits the growth of the vestibulocochlear nerve. (orig.)

  14. Development of amorphous silicon-germanium-alloys for stacked solar cells; Entwicklung von amorphen Silizium-Germanium-Legierungen fuer den Einsatz in Stapelsolarzellen

    Energy Technology Data Exchange (ETDEWEB)

    Lundszien, D.

    2001-01-01

    To obtain high efficiency silicon based thin film solar cells, the concept of stacked solar cells is routinely used. The use of component cells with different optical bandgaps provides a better utilization of the solar spectrum. In a stacked cell structure, a high quality narrow bandgap material is needed for the active layer of the bottom cell. Amorphous silicon-germanium-alloys (a-SiGe:H) have been successfully employed because of their tunable optical bandgap E{sub G} between 1.8 eV (a-Si:H) and 1.1 eV (a-Ge:H). Considerable effort has been put into the development of a-SiGe:H. Still, with increasing Ge content, the material shows a characteristic deterioration of its electronic properties, like an exponential increase of the defect density, thus counteracting the gain in absorption obtained for higher Ge contents. It is the defect density which has the dominant influence on carrier transport and cell efficiency by affecting the mobility lifetime product and the electric field in the devices. The performance of a-SiGe:H pin solar cells with a wide range of Ge contents i.e. a wide range of optical band gaps (E{sub G}=1.3 to 1.6 eV) are compared. It is demonstrated how the deterioration of the material properties can be overcome by careful adjustment of the device design and the use of highly reflective ZnO/Ag back contacts. (orig.)

  15. Electrically tunable liquid crystal photonic bandgap fiber laser

    DEFF Research Database (Denmark)

    Olausson, Christina Bjarnal Thulin; Scolari, Lara; Wei, Lei

    2010-01-01

    We demonstrate electrical tunability of a fiber laser by using a liquid crystal photonic bandgap fiber. Tuning of the laser is achieved by combining the wavelength filtering effect of a liquid crystal photonic bandgap fiber device with an ytterbium-doped photonic crystal fiber. We fabricate an all......-spliced laser cavity based on a liquid crystal photonic bandgap fiber mounted on a silicon assembly, a pump/signal combiner with single-mode signal feed-through and an ytterbium-doped photonic crystal fiber. The laser cavity produces a single-mode output and is tuned in the range 1040-1065nm by applying...

  16. Optimum design of band-gap beam structures

    DEFF Research Database (Denmark)

    Olhoff, Niels; Niu, Bin; Cheng, Gengdong

    2012-01-01

    -sectional area. To study the band-gap for travelling waves, a repeated inner segment of the optimized beams is analyzed using Floquet theory and the waveguide finite element (WFE) method. Finally, the frequency response is computed for the optimized beams when these are subjected to an external time......The design of band-gap structures receives increasing attention for many applications in mitigation of undesirable vibration and noise emission levels. A band-gap structure usually consists of a periodic distribution of elastic materials or segments, where the propagation of waves is impeded...

  17. Bandgap tuning in SrTi(N,O,F){sub 3} by anionic-lattice variation

    Energy Technology Data Exchange (ETDEWEB)

    Yoon, Songhak; Maegli, Alexandra E.; Karvonen, Lassi; Matam, Santhosh K.; Shkabko, Andrey [Laboratory for Solid State Chemistry and Catalysis, Empa-Swiss Federal Laboratories for Materials Science and Technology, CH-8600 Dübendorf (Switzerland); Riegg, Stefan [Lehrstuhl für Experimentalphysik 5, EKM, Universität Augsburg, Universitätsstraße 1, 86135 Augsburg (Germany); Großmann, Thomas; Ebbinghaus, Stefan G. [Institut für Chemie, Martin-Luther Universität Halle-Wittenberg, Kurt-Mothes-Straße 2, 06120 Halle/Saale (Germany); Pokrant, Simone [Laboratory for Solid State Chemistry and Catalysis, Empa-Swiss Federal Laboratories for Materials Science and Technology, CH-8600 Dübendorf (Switzerland); Weidenkaff, Anke, E-mail: anke.weidenkaff@empa.ch [Laboratory for Solid State Chemistry and Catalysis, Empa-Swiss Federal Laboratories for Materials Science and Technology, CH-8600 Dübendorf (Switzerland)

    2013-10-15

    Polycrystalline SrTiO{sub 3} and SrTi(O,F){sub 3} powders were synthesized by a solid-state reaction. A partial substitution of oxygen by nitrogen was subsequently carried out using thermal ammonolysis resulting in SrTi(N,O){sub 3} and SrTi(N,O,F){sub 3}. Powder X-ray diffraction (XRD) revealed a cubic perovskite structure with space group Pm-3m for all samples. The thermal ammonolysis slightly increased the lattice parameters, crystallite sizes and strain. As a result from the co-substitution of oxygen with nitrogen and fluorine for SrTi(N,O,F){sub 3}, highly distorted TiO{sub 6} octahedra were detected using X-ray absorption near edge structure (XANES) spectroscopy. The weakening of all active modes of the Raman spectra after thermal ammonolysis also indicated enhanced distortions in the local crystal structure. SrTi(N,O,F){sub 3} has the largest amount of nitrogen as well as fluorine among all four samples as determined by thermogravimetric analysis (TGA), elemental analysis and X-ray photoelectron spectroscopy (XPS). In the UV–vis spectra a distinctive shift of the absorption-edge energy was observed exclusively for the SrTi(N,O,F){sub 3} sample from 390 to 510 nm corresponding to a bandgap narrowing from 3.18 to 2.43 eV. - Graphical abstract: Figure shows the shift of the absorption-edge energy for the SrTi(N,O,F){sub 3} sample from 390 to 510 nm corresponding to a bandgap narrowing from 3.18 to 2.43 eV. Display Omitted - Highlights: • Synthesis of phase-pure SrTi(N,O,F){sub 3} via solid-state reaction. • The incorporated nitrogen contents increase by the presence of fluorine in SrTi(N,O,F){sub 3}. • Co-substitution with nitrogen and fluorine is beneficial for the bandgap narrowing compared to by only nitrogen or fluorine substitution.

  18. Efficient Planar Heterojunction Perovskite Solar Cells Based on Formamidinium Lead Bromide.

    Science.gov (United States)

    Hanusch, Fabian C; Wiesenmayer, Erwin; Mankel, Eric; Binek, Andreas; Angloher, Philipp; Fraunhofer, Christina; Giesbrecht, Nadja; Feckl, Johann M; Jaegermann, Wolfram; Johrendt, Dirk; Bein, Thomas; Docampo, Pablo

    2014-08-21

    The development of medium-bandgap solar cell absorber materials is of interest for the design of devices such as tandem solar cells and building-integrated photovoltaics. The recently developed perovskite solar cells can be suitable candidates for these applications. At present, wide bandgap alkylammonium lead bromide perovskite absorbers require a high-temperature sintered mesoporous TiO2 photoanode in order to function efficiently, which makes them unsuitable for some of the above applications. Here, we present for the first time highly efficient wide bandgap planar heterojunction solar cells based on the structurally related formamidinium lead bromide. We show that this material exhibits much longer diffusion lengths of the photoexcited species than its methylammonium counterpart. This results in planar heterojunction solar cells exhibiting power conversion efficiencies approaching 7%. Hence, formamidinium lead bromide is a strong candidate as a wide bandgap absorber in perovskite solar cells.

  19. Ultrafast electron and hole transfer in bulk heterojunctions of low-bandgap polymers

    Science.gov (United States)

    Kozlov, Oleg V.; Pavelyev, Vlad G.; de Gier, Hilde D.; Havenith, Remco W. A.; van Loosdrecht, Paul H. M.; Hummelen, Jan C.; Pshenichnikov, Maxim S.

    2016-12-01

    In modern bulk heterojunction (BHJ) organic solar cells, blends of low-bandgap polymer and [70]PCBM acceptor are used in the active layer. In this combination, the polymer absorbs photons from the red and near-IR parts of the solar spectrum, while the blue and near-UV photons are harvested by [70]PCBM. As a result, both electron transfer from polymer to [70]PCBM and hole transfer from [70]PCBM to polymer are of utmost importance in free charge generation and have to be optimized simultaneously. Here we study electron and hole transfer processes in BHJ blends of two low-bandgap polymers, BTT-DPP and PCPDTBT, by ultrafast photoinduced spectroscopy (PIA). By tracking the PIA dynamics, we observed substantially different charge separation pathways in BHJs of the two polymers with [70]PCBM. From the photoinduced anisotropy dynamics, we demonstrated that in the PCPDTBT:[70]PCBM system both electron and hole transfer processes are highly efficient, while in the BTTBPP:[ 70]PCBM electron transfer is blocked due to the unfortunate energy level alignment leaving hole transfer the only pathway to free charge generation. Calculations at the density functional theory level are used to gain more insight into our findings. The presented results highlight the importance of the energy level alignment on the charge separation process.

  20. Low bandgap polymers synthesized by FeCl{sub 3} oxidative polymerization

    Energy Technology Data Exchange (ETDEWEB)

    Cai, Tianqi [Materials and Surface Chemistry/Polymer Technology, Chalmers University of Technology, SE-412 96 Goeteborg (Sweden); School of Materials Science and Engineering, East China University of Science and Technology, Meilong Road 130, 200237 Shanghai (China); Zhou, Yi; Zhang, Fengling; Inganaes, Olle [Biomolecular and Organic Electronics, IFM, and Centre of Organic Electronics, Linkoeping University, SE-581 83 Linkoeping (Sweden); Wang, Ergang; Hellstroem, Stefan [Materials and Surface Chemistry/Polymer Technology, Chalmers University of Technology, SE-412 96 Goeteborg (Sweden); Xu, Shiai [School of Materials Science and Engineering, East China University of Science and Technology, Meilong Road 130, 200237 Shanghai (China); Andersson, Mats R. [Materials and Surface Chemistry/Polymer Technology, Chalmers University of Technology, SE-412 96 Goeteborg (Sweden); Biomolecular and Organic Electronics, IFM, and Centre of Organic Electronics, Linkoeping University, SE-581 83 Linkoeping (Sweden)

    2010-07-15

    Four low bandgap polymers, combining an alkyl thiophene donor with benzo[c][1,2,5]thiadiazole, 2,3-diphenylquinoxaline, 2,3-diphenylthieno[3,4-b]pyrazine and 6,7-diphenyl-[1,2,5]thiadiazolo[3,4-g]quinoxaline acceptors in a donor-acceptor-donor architecture, were synthesized via FeCl{sub 3} oxidative polymerization. The molecular weights of the polymers were improved by introducing o-dichlorobenzene (ODCB) as the reaction solvent instead of the commonly used solvent, chloroform. The photophysical, electrochemical and photovoltaic properties of the resulting polymers were investigated and compared. The optical bandgaps of the polymers vary between 1.0 and 1.9 eV, which is promising for solar cells. The devices spin-coated from an ODCB solution of P1DB:[70]PCBM showed a power conversion efficiency of 1.08% with an open-circuit voltage of 0.91 V and a short-circuit current density of 3.36 mA cm{sup -2} under irradiation from an AM1.5G solar simulator (100 mW cm{sup -2}). (author)

  1. Microstructured and Photonic Bandgap Fibers for Applications in the Resonant Bio- and Chemical Sensors

    Directory of Open Access Journals (Sweden)

    Maksim Skorobogatiy

    2009-01-01

    Full Text Available We review application of microstructured and photonic bandgap fibers for designing resonant optical sensors of changes in the value of analyte refractive index. This research subject has recently invoked much attention due to development of novel fiber types, as well as due to development of techniques for the activation of fiber microstructure with functional materials. Particularly, we consider two sensors types. The first sensor type employs hollow core photonic bandgap fibers where core guided mode is confined in the analyte filled core through resonant effect in the surrounding periodic reflector. The second sensor type employs metalized microstructured or photonic bandgap waveguides and fibers, where core guided mode is phase matched with a plasmon propagating at the fiber/analyte interface. In resonant sensors one typically employs fibers with strongly nonuniform spectral transmission characteristics that are sensitive to changes in the real part of the analyte refractive index. Moreover, if narrow absorption lines are present in the analyte transmission spectrum, due to Kramers-Kronig relation this will also result in strong variation in the real part of the refractive index in the vicinity of an absorption line. Therefore, resonant sensors allow detection of minute changes both in the real part of the analyte refractive index (10−6–10−4 RIU, as well as in the imaginary part of the analyte refractive index in the vicinity of absorption lines. In the following we detail various resonant sensor implementations, modes of operation, as well as analysis of sensitivities for some of the common transduction mechanisms for bio- and chemical sensing applications. Sensor designs considered in this review span spectral operation regions from the visible to terahertz.

  2. Optimum design of band-gap beam structures

    DEFF Research Database (Denmark)

    Olhoff, Niels; Niu, Bin; Cheng, Gengdong

    2012-01-01

    -sectional area. To study the band-gap for travelling waves, a repeated inner segment of the optimized beams is analyzed using Floquet theory and the waveguide finite element (WFE) method. Finally, the frequency response is computed for the optimized beams when these are subjected to an external time......The design of band-gap structures receives increasing attention for many applications in mitigation of undesirable vibration and noise emission levels. A band-gap structure usually consists of a periodic distribution of elastic materials or segments, where the propagation of waves is impeded...... or significantly suppressed for a range of external excitation frequencies. Maximization of the band-gap is therefore an obvious objective for optimum design. This problem is sometimes formulated by optimizing a parameterized design model which assumes multiple periodicity in the design. However, it is shown...

  3. High Power Wide Bandgap Engineered MMW MMIC Transceiver Project

    Data.gov (United States)

    National Aeronautics and Space Administration — During this phase I SBIR effort unique proven lattice and bandgap engineering techniques will be utilized to epitaxially grow InAlAs / InGaAs on GaN substrate for...

  4. Design of Bandgap Reference in Switching Power Supply

    Institute of Scientific and Technical Information of China (English)

    XU Li; NIU Ping-juan; FU Xian-song; DING Ke; PENG Xiao-lei

    2009-01-01

    A bandgap voltage reference is designed to meet the requirements of low power loss,low temperature coefficient and high power source rejection ratio(PSRR) in the intergrated circuit.Based on the analysis of conventional bandgap reference circuit,and combined with the integral performance of IC,the specific design index of the bandgap reference is put forward.In the meantime,the circuit and the layout are designed with Chartered 0.35 μm dual gate CMOS process.The simulation result shows that the coefficient is less than 30ppm/℃ with the temperature from -50℃ to 150℃. The bandgap reference has the characteristics of low power and high PSRR.

  5. Investigation of colloidal PbS quantum dot-based solar cells with near infrared emission.

    Science.gov (United States)

    Lim, Sungoh; Kim, Yohan; Lee, Jeongno; Han, Chul Jong; Kang, Jungwon; Kim, Jiwan

    2014-12-01

    Colloidal quantum dots (QD)-based solar cells with near infrared (NIR) emission have been investigated. Lead sulfide (PbS) QDs, which have narrow band-gap and maximize the absorption of NIR spectrum, were chosen as active materials for efficient solar cells. The inverted structure of indium tin oxide/titanium dioxide/PbS QDs/poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate)/silver (ITO/TiO2/PbS QDs/ PSS/Ag) was applied for favorable electron and hole seperation from the PbS QD. Through the ligand exchange by 1,2-Ethanedithiol (EDT), the interparticle distance of the PbS QDs in thin film became closer and the performance of the PbS QD-based solar cells was improved. Our PbS QD-based inverted solar cells showed open circuit voltages (V(oc)) of 0.33 V, short circuit current density (J(sc)) of 10.89 mA/cm2, fill factor (FF) of 30%, and power conversion efficiency (PCE) of 1.11%. In our PbS QD-based multifunctional solar cell, the NIR light emission intensity was simply detected with photodiode system, which implies the potential of multi-functional diode device for various applications.

  6. Nanocrystalline germanium nip solar cells with spectral sensitivities extending into 1450 nm

    Science.gov (United States)

    Li, Chang; Ni, Jian; Sun, Xiaoxiang; Wang, Xinyu; Li, Zhenglong; Cai, Hongkun; Li, Juan; Zhang, Jianjun

    2017-02-01

    To absorb the infrared part of the solar spectrum more efficiently, narrow bandgap hydrogenated nanocrystalline germanium (nc-Ge:H) thin films were fabricated by radio frequency plasma enhanced chemical vapor deposition at a low temperature of 180 °C. While the incubation layer of the nc-Ge:H was reduced to less than 5 nm by using the ultra-high hydrogen dilution, the negative photoconductivity behavior was still observed as the thickness of nc-Ge:H up to 30 nm. Therefore, as the best candidate for solar cells application, the nc-Ge:H (20 nm)/nc-Si:H (10 nm) periodic multilayer structure was prepared and used as the absorption layer of nc-Ge:H nip solar cells. More importantly, the spectral sensitivities extending into the wavelength of 1450 nm were achieved in the nc-Ge:H nip solar cells. In addition, the annealing for the nc-Ge:H nip solar cells was carried out. While the overall short circuit current density of the device is improved after 500 °C annealing, the spectral sensitivities in the infrared region is decreased due to the the coalescence of Ge crystallites.

  7. Wide-bandgap III-Nitride based Second Harmonic Generation

    Science.gov (United States)

    2014-10-02

    Jun-2014 Approved for Public Release; Distribution Unlimited Final Report: Wide-bandgap III - Nitride based Second Harmonic Generation The views...Report: Wide-bandgap III - Nitride based Second Harmonic Generation Report Title It was demonstrated that GaN, AlGaN and AlN lateral polar structures can...research have been socialized to the III - Nitride Optoelectronics Center of Excellence (ARL SEDD) and to the 2013 ARO Staff Research Symposium and at

  8. Bandgap Restructuring of the Layered Semiconductor Gallium Telluride in Air.

    Science.gov (United States)

    Fonseca, Jose J; Tongay, Sefaattin; Topsakal, Mehmet; Chew, Annabel R; Lin, Alan J; Ko, Changhyun; Luce, Alexander V; Salleo, Alberto; Wu, Junqiao; Dubon, Oscar D

    2016-08-01

    A giant bandgap reduction in layered GaTe is demonstrated. Chemisorption of oxygen to the Te-terminated surfaces produces significant restructuring of the conduction band resulting in a bandgap below 0.8 eV, compared to 1.65 eV for pristine GaTe. Localized partial recovery of the pristine gap is achieved by thermal annealing, demonstrating that reversible band engineering in layered semiconductors is accessible through their surfaces.

  9. Large-area single-mode photonic bandgap vcsels

    DEFF Research Database (Denmark)

    Birkedal, Dan; Gregersen, N.; Bischoff, S.;

    2003-01-01

    We demonstrate that the photonic bandgap effect can be used to control the modes of large area vertical cavity surface emitting lasers. We obtain more than 20 dB side mode suppression ratios in a 10-micron area device.......We demonstrate that the photonic bandgap effect can be used to control the modes of large area vertical cavity surface emitting lasers. We obtain more than 20 dB side mode suppression ratios in a 10-micron area device....

  10. Degenerate four wave mixing in solid core photonic bandgap fibers

    DEFF Research Database (Denmark)

    Rasmussen, Per Dalgaard; Lægsgaard, Jesper; Bang, Ole

    2008-01-01

    Degenerate four wave mixing in solid core photonic bandgap fibers is studied theoretically. We demonstrate the possibility of generating parametric gain across bandgaps, and propose a specific design suited for degenerate four wave mixing when pumping at 532nmm. the possibility of tuning the effi...... the efficency of the parametric gain by varying the temperature is also considered. The sults are verified by numerical simultations of pulse propagation....

  11. Transmission properties of hollow-core photonic bandgap fibers

    DEFF Research Database (Denmark)

    Falk, Charlotte Ijeoma; Hald, Jan; Petersen, Jan C.

    2010-01-01

    Variations in optical transmission of four types of hollow-core photonic bandgap fibers are measured as a function of laser frequency. These variations influence the potential accuracy of gas sensors based on molecular spectroscopy in hollow-core fibers.......Variations in optical transmission of four types of hollow-core photonic bandgap fibers are measured as a function of laser frequency. These variations influence the potential accuracy of gas sensors based on molecular spectroscopy in hollow-core fibers....

  12. Bandgap calculations and trends of organometal halide perovskites

    DEFF Research Database (Denmark)

    Castelli, Ivano Eligio; García Lastra, Juan Maria; Thygesen, Kristian Sommer

    2014-01-01

    of Cs, CH3NH3, and HC(NH2)2 as A-cation, Sn and Pb as B-ion, and a combination of Cl, Br, and I as anions. The calculated gaps span over a region from 0.5 to 5.0 eV. In addition, the trends over bandgaps have been investigated: the bandgap increases with an increase of the electronegativities...

  13. Bandgap modulation in photoexcited topological insulator Bi2Te3 via atomic displacements

    Science.gov (United States)

    Hada, Masaki; Norimatsu, Katsura; Tanaka, Sei'ichi; Keskin, Sercan; Tsuruta, Tetsuya; Igarashi, Kyushiro; Ishikawa, Tadahiko; Kayanuma, Yosuke; Miller, R. J. Dwayne; Onda, Ken; Sasagawa, Takao; Koshihara, Shin-ya; Nakamura, Kazutaka G.

    2016-07-01

    The atomic and electronic dynamics in the topological insulator (TI) Bi2Te3 under strong photoexcitation were characterized with time-resolved electron diffraction and time-resolved mid-infrared spectroscopy. Three-dimensional TIs characterized as bulk insulators with an electronic conduction surface band have shown a variety of exotic responses in terms of electronic transport when observed under conditions of applied pressure, magnetic field, or circularly polarized light. However, the atomic motions and their correlation between electronic systems in TIs under strong photoexcitation have not been explored. The artificial and transient modification of the electronic structures in TIs via photoinduced atomic motions represents a novel mechanism for providing a comparable level of bandgap control. The results of time-domain crystallography indicate that photoexcitation induces two-step atomic motions: first bismuth and then tellurium center-symmetric displacements. These atomic motions in Bi2Te3 trigger 10% bulk bandgap narrowing, which is consistent with the time-resolved mid-infrared spectroscopy results.

  14. Research and development of photovoltaic power system. Optimization of bandgap of chalcopyrite semiconductors; Taiyoko hatsuden system no kenkyu kaihatsu. Kinseitaihaba no saitekika no kenkyu

    Energy Technology Data Exchange (ETDEWEB)

    Konagai, M. [Tokyo Institute of Technology, Tokyo (Japan). Faculty of Engineering

    1994-12-01

    This paper reports the result obtained during fiscal 1994 on research on research on optimization of bandgap in thin film compound solar cells. In research on Cu(InGa)Se2 thin film solar cells by using a gas phase selenide making process, discussions were given on optimizing the following three processes: a process to raise temperature of a precursor film formed at a substrate temperature of about 150{degree}C, a selenide making process to perform annealing at about 500{degree}C, and a temperature reducing process. Good characteristics were obtained when selenium amount in the precursor is about 50%. In a bandgap control viewpoint, it was found that the conversion efficiency decreases rapidly when Ga composition is higher than 50%. A conversion efficiency of 14.9% was obtained to date at the Ga/(In+Ga) ratio of 0.4. In research on Cu(InGa)Se2 thin film solar cells by using a simultaneous deposition method, a conversion efficiency of 13.5% was obtained at a bandgap width of about 1.3 eV during research on manufacturing ZnO/CdS/Cu(InGa)Se2 thin film solar cells by using the simultaneous deposition method. Research has been carried out on manufacturing Cu(InGa)Se2 thin film solar cells using ZnSe interface layers. 8 figs.

  15. Siemens solar CIS photovoltaic module and system performance at the National Renewable Energy Laboratory

    Energy Technology Data Exchange (ETDEWEB)

    Strand, T.; Kroposki, B.; Hansen, R. [National Renewable Energy Lab., Golden, CO (United States); Willett, D. [Siemens Solar Industries, Camarillo, CA (United States)

    1996-05-01

    This paper evaluates the individual module and array performance of Siemens Solar Industries copper indium diselenide (CIS) polycrystalline thin-film technology. This is accomplished by studying module and array performance over time. Preliminary temperature coefficients for maximum power, maximum-power voltage, maximum-power current, open-circuit voltage, short-circuit current, and fill factor are determined at both the module and array level. These coefficients are used to correct module/array performance to 25{degrees}C to evaluate stability. The authors show that CIS exhibits a strong inverse correlation between array power and back-of-module temperature. This is due mainly to the narrow bandgap of the CIS material, which results in a strong inverse correlation between voltage and temperature. They also show that the temperature-corrected module and array performance has been relatively stable over the evaluation interval ({approx}2 years).

  16. On the Suppression Band and Bandgap of Planar Electromagnetic Bandgap Structures

    Directory of Open Access Journals (Sweden)

    Baharak Mohajer-Iravani

    2014-01-01

    Full Text Available Electromagnetic bandgap structures are considered a viable solution for the problem of switching noise in printed circuit boards and packages. Less attention, however, has been given to whether or not the introduction of EBGs affects the EMI potential of the circuit to couple unwanted energy to neighboring layers or interconnects. In this paper, we show that the bandgap of EBG structures, as generated using the Brillouin diagram, does not necessarily correspond to the suppression bandwidth typically generated using S-parameters. We show that the reactive near fields radiating from openings within the EBG layers can be substantial and are present in the entire frequency band including propagating and nonpropagating mode regions. These fields decay fast with distance; however, they can couple significant energy to adjacent layers and to signal lines. The findings are validated using full-wave three-dimensional numerical simulation. Based on this work, design guidelines for EBG structures can be drawn to insure not only suppression of switching noise but also minimization of EMI and insuring signal integrity.

  17. Simulation Design for Rutile-TiO2 Nanostructures with a Large Complete-Photonic Bandgap in Electrolytes

    Directory of Open Access Journals (Sweden)

    Toshihiro Isobe

    2012-10-01

    Full Text Available The photonic bands of various TiO2 2D photonic crystals, i.e., cylindrical, square and hexagonal columns connected with/without walls and filled with acetonitrile, were investigated from the perspective of dye-sensitized solar cells. The finite-difference time-domain methods revealed that two-dimensional (2D photonic crystals with rods connected with walls composed of TiO2 and electrolytes had complete photonic band gaps under specific conditions. This optimally designed bandgap reaches a large Δω/ωmid value, 1.9%, in a triangular array of square rods connected with walls, which is the largest complete 2D bandgap thus far reported for a photochemical system. These discoveries would promote the photochemical applications of photonic crystals.

  18. Direct bandgap GeSn light emitting diodes for short-wave infrared applications grown on Si

    Science.gov (United States)

    von den Driesch, Nils; Stange, Daniela; Wirths, Stephan; Rainko, Denis; Mussler, Gregor; Stoica, Toma; Ikonic, Zoran; Hartmann, Jean-Michel; Grützmacher, Detlev; Mantl, Siegfried; Buca, Dan

    2016-03-01

    The experimental demonstration of fundamental direct bandgap, group IV GeSn alloys has constituted an important step towards realization of the last missing ingredient for electronic-photonic integrated circuits, i.e. the efficient group IV laser source. In this contribution, we present electroluminescence studies of reduced-pressure CVD grown, direct bandgap GeSn light emitting diodes (LEDs) with Sn contents up to 11 at.%. Besides homojunction GeSn LEDs, complex heterojunction structures, such as GeSn/Ge multi quantum wells (MQWs) have been studied. Structural and compositional investigations confirm high crystalline quality, abrupt interfaces and tailored strain of the grown structures. While also being suitable for light absorption applications, all devices show light emission in a narrow short-wave infrared (SWIR) range. Temperature dependent electroluminescence (EL) clearly indicates a fundamentally direct bandgap in the 11 at.% Sn sample, with room temperature emission at around 0.55 eV (2.25 µm). We have, however, identified some limitations of the GeSn/Ge MQW approach regarding emission efficiency, which can be overcome by introducing SiGeSn ternary alloys as quantum confinement barriers.

  19. Influence of transition metal doping (X  =  Mn, Fe, Co, Ni) on the structure and bandgap of ferroelectric Bi3.15Nd0.85Ti2X1O12

    Science.gov (United States)

    Chen, Xiaoqin; Huang, Feng; Lu, Zhangwu; Xue, Yun; Min, Jingjing; Li, Jihui; Xiao, Jun; Yang, Fujun; Zeng, Xiangbin

    2017-03-01

    Although the internal field can effectively maintain the separation between photo-excited charge carriers, the wide bandgap restrains ferroelectric materials from visible light absorption. This study examined the effects of transition metal (TM) Mn, Fe, Co or Ni doping on the structure and bandgap of Bi3.15Nd0.85Ti3O12 (BNdT) prepared by the molten salt synthesis method. No other non-bismuth layered structure phases were introduced. Mn, Co or Ni doping does not change the three-layered perovskite structure of BNdT while Fe doping increases the layer number from three to four. The doping of TM ions decreases the bandgap obviously. Among them, Mn-doped BNdT shows the largest bandgap reduction by ~1.6 eV. The narrowed bandgap was discussed to be attributed to the electronegativity of TM ions and the lattice distortion induced by doping together. The present work provides an available way to control the bandgap of complex oxide materials and provides a new tool for manipulating oxide optoelectronics.

  20. Direct-Indirect Nature of the Bandgap in Lead-Free Perovskite Nanocrystals.

    Science.gov (United States)

    Zhang, Yuhai; Yin, Jun; Parida, Manas R; Ahmed, Ghada H; Pan, Jun; Bakr, Osman M; Brédas, Jean-Luc; Mohammed, Omar F

    2017-07-20

    With record efficiencies achieved in lead halide perovskite-based photovoltaics, urgency has shifted toward finding alternative materials that are stable and less toxic. Bismuth-based perovskite materials are currently one of the most promising candidates among those alternatives. However, the band structures of these materials, including the nature of the bandgaps, remain elusive due to extremely low photoluminescence quantum yield (PLQY) and scattering issues in their thin-film form. Here, we reveal the specific nature of the material's electronic transitions by realizing monodisperse colloidal nanocrystals (NCs) of hexagonal-phase Cs3Bi2X9 perovskites, which afford well-resolved PL features. Interestingly, the PL profile exhibits a dual-spectral feature at room temperature with comparable intensities, based on which we propose an exciton recombination process involving both indirect and direct transitions simultaneously-an observation further supported by temperature-dependent and density functional theory (DFT) calculations. Our findings provide experimental and theoretical insights into the nature of the bandgaps in bismuth halide materials-essential information for assessing their viability in solar cells and optoelectronics.

  1. Direct-Indirect Nature of the Bandgap in Lead-Free Perovskite Nanocrystals

    KAUST Repository

    Zhang, Yuhai

    2017-06-23

    With record efficiencies achieved in lead halide perovskite-based photovoltaics, urgency has shifted toward finding alternative materials that are stable and less toxic. Bismuth-based perovskite materials are currently one of the most promising candidates among those alternatives. However, the band structures of these materials, including the nature of the bandgaps, remain elusive due to extremely low photoluminescence quantum yield (PLQY) and scattering issues in their thin-film form. Here, we reveal the specific nature of the material\\'s electronic transitions by realizing monodisperse colloidal nanocrystals (NCs) of hexagonal-phase Cs3Bi2X9 perovskites, which afford well-resolved PL features. Interestingly, the PL profile exhibits a dual-spectral feature at room temperature with comparable intensities, based on which we propose an exciton recombination process involving both indirect and direct transitions simultaneously-an observation further supported by temperature-dependent and density functional theory (DFT) calculations. Our findings provide experimental and theoretical insights into the nature of the bandgaps in bismuth halide materials-essential information for assessing their viability in solar cells and optoelectronics.

  2. The Miscibility of PCBM in Low Band-Gap Conjugated Polymers in Organic Photovoltaics

    Science.gov (United States)

    Chen, Huipeng; You, Wei; Peet, Jeff; Azoulay, Jason; Bazan, Guillermo; Dadmun, Mark

    2012-02-01

    Understanding the morphology of the photoactive layer in organic photovoltaics (OPVs) is essential to optimizing conjugated polymer-based solar cells to meet the targeted efficiency of 10%. The miscibility and interdiffusion of components are among the key elements that impact the development of morphology and structure in OPV active layers. This study uses neutron reflectivity to correlate the structure of low band gap polymers to their miscibility with PCBM. Several low band gap polymers that exhibit power conversion efficiencies exceeding 7%, including PBnDT-DTffBT were examined. The intermixing of low band-gap polymer and PCBM bilayers was monitored by neutron reflectivity before and after thermal annealing, providing quantification of the miscibility and interdiffusion of PCBM within the low band gap polymer layer. These results indicate that the miscibility of PCBM ranges from 3% to 26% with the low band-gap polymers studied. The correlation between low band gap polymer structure and miscibility of PCBM will also be discussed.

  3. Chemical and Bandgap Engineering in Monolayer Hexagonal Boron Nitride

    Science.gov (United States)

    Ba, Kun; Jiang, Wei; Cheng, Jingxin; Bao, Jingxian; Xuan, Ningning; Sun, Yangye; Liu, Bing; Xie, Aozhen; Wu, Shiwei; Sun, Zhengzong

    2017-04-01

    Monolayer hexagonal boron nitride (h-BN) possesses a wide bandgap of ~6 eV. Trimming down the bandgap is technically attractive, yet poses remarkable challenges in chemistry. One strategy is to topological reform the h-BN’s hexagonal structure, which involves defects or grain boundaries (GBs) engineering in the basal plane. The other way is to invite foreign atoms, such as carbon, to forge bizarre hybrid structures like hetero-junctions or semiconducting h-BNC materials. Here we successfully developed a general chemical method to synthesize these different h-BN derivatives, showcasing how the chemical structure can be manipulated with or without a graphene precursor, and the bandgap be tuned to ~2 eV, only one third of the pristine one’s.

  4. Bandgap renormalization in single-wall carbon nanotubes.

    Science.gov (United States)

    Zhu, Chunhui; Liu, Yujie; Xu, Jieying; Nie, Zhonghui; Li, Yao; Xu, Yongbing; Zhang, Rong; Wang, Fengqiu

    2017-09-11

    Single-wall carbon nanotubes (SWNTs) have been extensively explored as an ultrafast nonlinear optical material. However, due to the numerous electronic and morphological arrangements, a simple and self-contained physical model that can unambiguously account for the rich photocarrier dynamics in SWNTs is still absent. Here, by performing broadband degenerate and non-degenerate pump-probe experiments on SWNTs of different chiralities and morphologies, we reveal strong evidences for the existence of bandgap renormalization in SWNTs. In particularly, it is found that the broadband transient response of SWNTs can be well explained by the combined effects of Pauli blocking and bandgap renormalization, and the distinct dynamics is further influenced by the different sensitivity of degenerate and non-degenerate measurements to these two concurrent effects. Furthermore, we attribute optical-phonon bath thermalization as an underlying mechanism for the observed bandgap renormalization. Our findings provide new guidelines for interpreting the broadband optical response of carbon nanotubes.

  5. Ultrasensitive twin-core photonic bandgap fiber refractive index sensor

    DEFF Research Database (Denmark)

    Yuan, Scott Wu; Town, Graham; Bang, Ole

    2009-01-01

    We propose a microfluidic refractive index sensor based on new polymer twin-core photonic bandgap fiber (PBGF). The sensor can achieve ultrahigh detection limit, i.e. >1.4times10-7RIU refractive index unit (RIU), by measuring the coupling wavelength shift.......We propose a microfluidic refractive index sensor based on new polymer twin-core photonic bandgap fiber (PBGF). The sensor can achieve ultrahigh detection limit, i.e. >1.4times10-7RIU refractive index unit (RIU), by measuring the coupling wavelength shift....

  6. Compact electrically controlled broadband liquid crystal photonic bandgap fiber polarizer

    DEFF Research Database (Denmark)

    Wei, Lei; Alkeskjold, Thomas Tanggaard; Bjarklev, Anders Overgaard

    2009-01-01

    An electrically controlled liquid crystal photonic-bandgap fiber polarizer is experimentally demonstrated. A maximum 21.3dB electrically tunable polarization extinction ratio is achieved with 45° rotatable transmission axis as well as switched on and off in 1300nm–1600nm.......An electrically controlled liquid crystal photonic-bandgap fiber polarizer is experimentally demonstrated. A maximum 21.3dB electrically tunable polarization extinction ratio is achieved with 45° rotatable transmission axis as well as switched on and off in 1300nm–1600nm....

  7. The band-gap enhanced photovoltaic structure

    Science.gov (United States)

    Tessler, Nir

    2016-05-01

    We critically examine the recently suggested structure that was postulated to potentially add 50% to the photo-conversion efficiency of organic solar cells. We find that the structure could be realized using stepwise increase in the gap as long as the steps are not above 0.1 eV. We also show that the charge extraction is not compromised due to an interplay between the contact's space charge and the energy level modification, which result in a flat energy band at the extracting contact.

  8. Effect of Dielectric Constant Contrast and Filling Factor to Photonic Bandgap

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    The effect of dielectric constant contrast and the filling factor to the photonic bandgap in a 2-D square lattice photonic crystal is discussed. The location, width and number of photonic bandgap can be modulated.

  9. Solar upconversion with plasmon-enhanced bimolecular complexes

    Energy Technology Data Exchange (ETDEWEB)

    Dionne, Jennifer [Stanford Univ., CA (United States)

    2017-04-14

    Upconversion of sub-bandgap photons is a promising approach to exceed the Shockley-Queisser limit in solar technologies. However, due to the low quantum efficiencies and narrow absorption bandwidths of upconverters, existing systems have only led to fractional percent improvements in photovoltaic devices (~0.01%). In this project, we aimed to develop an efficient upconverting material that could improve cell efficiencies by at least one absolute percent. To achieve this goal, we first used thermodynamic calculations to determine cell efficiencies with realistic upconverting materials. Then, we designed, synthesized, and characterized nanoantennas that promise >100x enhancement in both the upconverter absorption cross-section and emissive radiative rate. Concurrently, we optimized the upconverer by designing new ionic and molecular complexes that promise efficient solid-state upconversion. Lastly, with Bosch, we simulated record-efficiency semi-transparent cells that will allow for ready incorporation of our upconverting materials. While we were not successful in designing record efficiency upconverters during our three years of funding, we gained significant insight into the existing limitations of upconverters and how to best address these challenges. Ongoing work is aimed at addressing these limitations, to make upconversion a cost-competitive solar technology in future years.

  10. High-power Yb-doped photonic bandgap fiber amplifier at 1150-1200 nm

    DEFF Research Database (Denmark)

    Shirakawa, A; Maruyama, H; Ueda, K

    2009-01-01

    Ytterbium-doped solid-core photonic bandgap fiber amplifiers operating at the long-wavelength edge of the ytterbium gain band are reported. The low-loss bandgap transmission window is formed in the very low gain region, whilst outside the bandgap, large attenuation inhibits the exponential growth...... knowledge, these are the highest output powers generating from active photonic bandgap fibers, as well as from ytterbium-doped fiber lasers at these wavelengths. (C) 2009 Optical Society of America...

  11. Thieno[3,4-c]Pyrrole-4,6-Dione-Based Polymer Acceptors for High Open-Circuit Voltage All-Polymer Solar Cells

    KAUST Repository

    Liu, Shengjian

    2017-04-20

    While polymer acceptors are promising fullerene alternatives in the fabrication of efficient bulk heterojunction (BHJ) solar cells, the range of efficient material systems relevant to the “all-polymer” BHJ concept remains narrow, and currently limits the perspectives to meet the 10% efficiency threshold in all-polymer solar cells. This report examines two polymer acceptor analogs composed of thieno[3,4-c]pyrrole-4,6-dione (TPD) and 3,4-difluorothiophene ([2F]T) motifs, and their BHJ solar cell performance pattern with a low-bandgap polymer donor commonly used with fullerenes (PBDT-TS1; taken as a model system). In this material set, the introduction of a third electron-deficient motif, namely 2,1,3-benzothiadiazole (BT), is shown to (i) significantly narrow the optical gap (Eopt) of the corresponding polymer (by ≈0.2 eV) and (ii) improve the electron mobility of the polymer by over two orders of magnitude in BHJ solar cells. In turn, the narrow-gap P2TPDBT[2F]T analog (Eopt = 1.7 eV) used as fullerene alternative yields high open-circuit voltages (VOC) of ≈1.0 V, notable short-circuit current values (JSC) of ≈11.0 mA cm−2, and power conversion efficiencies (PCEs) nearing 5% in all-polymer BHJ solar cells. P2TPDBT[2F]T paves the way to a new, promising class of polymer acceptor candidates.

  12. Quantum Junction Solar Cells

    KAUST Repository

    Tang, Jiang

    2012-09-12

    Colloidal quantum dot solids combine convenient solution-processing with quantum size effect tuning, offering avenues to high-efficiency multijunction cells based on a single materials synthesis and processing platform. The highest-performing colloidal quantum dot rectifying devices reported to date have relied on a junction between a quantum-tuned absorber and a bulk material (e.g., TiO 2); however, quantum tuning of the absorber then requires complete redesign of the bulk acceptor, compromising the benefits of facile quantum tuning. Here we report rectifying junctions constructed entirely using inherently band-aligned quantum-tuned materials. Realizing these quantum junction diodes relied upon the creation of an n-type quantum dot solid having a clean bandgap. We combine stable, chemically compatible, high-performance n-type and p-type materials to create the first quantum junction solar cells. We present a family of photovoltaic devices having widely tuned bandgaps of 0.6-1.6 eV that excel where conventional quantum-to-bulk devices fail to perform. Devices having optimal single-junction bandgaps exhibit certified AM1.5 solar power conversion efficiencies of 5.4%. Control over doping in quantum solids, and the successful integration of these materials to form stable quantum junctions, offers a powerful new degree of freedom to colloidal quantum dot optoelectronics. © 2012 American Chemical Society.

  13. Optically controlled photonic bandgap structures for microstrip circuits

    CERN Document Server

    Cadman, D A

    2003-01-01

    This thesis is concerned with the optical control of microwave photonic bandgap circuits using high resistivity silicon. Photoconducting processes that occur within silicon are investigated. The influence of excess carrier density on carrier mobility and lifetime is examined. In addition, electron-hole pair recombination mechanisms (Shockley-Read-Hall, Auger, radiative and surface) are investigated. The microwave properties of silicon are examined, in particular the variation of silicon reflectivity with excess carrier density. Filtering properties of microstrip photonic bandgap structures and how they may be controlled optically are studied. A proof-of-concept microstrip photonic bandgap structure with optical control is designed, simulated and measured. With no optical illumination incident upon the silicon, the microstrip photonic bandgap structure's filtering properties are well-defined; a 3dB stopband width of 2.6GHz, a 6dB bandwidth of 2GHz and stopband depth of -11.6dB at the centre frequency of 9.9GHz...

  14. AlN Bandgap Temperature Dependence from its Optical Properties

    Science.gov (United States)

    2008-06-07

    AlN bandgap temperature dependence from its optical properties E. Silveira a,, J.A. Freitas b, S.B. Schujman c, L.J. Schowalter c a Depto. de Fisica ...range. The energy gap in semiconductors in general changes due to contributions from the electron–phonon interaction and due to the lattice thermal

  15. Spontaneous emission and nonlinear effects in photonic bandgap materials

    Science.gov (United States)

    Fogel, Ishella S.; Bendickson, Jon M.; Tocci, Michael D.; Bloemer, Mark J.; Scalora, Michael; Bowden, Charles M.; Dowling, Jonathan P.

    1998-03-01

    We summarize and review our theoretical and experimental work on spontaneous emission and nonlinear effects in one-dimensional, photonic bandgap (PBG) structures. We present a new result: a method for calculating the normal-mode solutions - and hence the spontaneous emission of embedded emitters - in an arbitrary, linear, lossless, one-dimensional, PBG structure.

  16. Mode Division Multiplexing Exploring Hollow-Core Photonic Bandgap Fibers

    DEFF Research Database (Denmark)

    Xu, Jing; Lyngso, Jens Kristian; Leick, Lasse

    2013-01-01

    We review our recent exploratory investigations on mode division multiplexing using hollow-core photonic bandgap fibers (HC-PBGFs). Compared with traditional multimode fibers, HC-PBGFs have several attractive features such as ultra-low nonlinearities, low-loss transmission window around 2 µm etc....

  17. Liquid Crystal Photonic bandgap Fibers: Modeling and Devices

    DEFF Research Database (Denmark)

    Weirich, Johannes

    In this PhD thesis an experimental and numerical investigation of liquid crystal infiltrated photonic bandgap fibers (LCPBGs) is presented. A simulation scheme for modeling LCPBG devices including electrical tunability is presented. New experimental techniques, boundary coating and the applicatio...

  18. Analysis of photonic band-gap structures in stratified medium

    DEFF Research Database (Denmark)

    Tong, Ming-Sze; Yinchao, Chen; Lu, Yilong;

    2005-01-01

    Purpose - To demonstrate the flexibility and advantages of a non-uniform pseudo-spectral time domain (nu-PSTD) method through studies of the wave propagation characteristics on photonic band-gap (PBG) structures in stratified medium Design/methodology/approach - A nu-PSTD method is proposed...

  19. Design for maximum band-gaps in beam structures

    DEFF Research Database (Denmark)

    Olhoff, Niels; Niu, Bin; Cheng, Gengdong

    2012-01-01

    This paper aims to extend earlier optimum design results for transversely vibrating Bernoulli-Euler beams by determining new optimum band-gap beam structures for (i) different combinations of classical boundary conditions, (ii) much larger values of the orders n and n-1 of adjacent upper and lowe...

  20. Advances in wide bandgap SiC for optoelectronics

    DEFF Research Database (Denmark)

    Ou, Haiyan; Ou, Yiyu; Argyraki, Aikaterini

    2014-01-01

    Silicon carbide (SiC) has played a key role in power electronics thanks to its unique physical properties like wide bandgap, high breakdown field, etc. During the past decade, SiC is also becoming more and more active in optoelectronics thanks to the progress in materials growth and nanofabrication...

  1. Photonic bandgap structures for long-range surface plasmon polaritons

    DEFF Research Database (Denmark)

    Bozhevolnyi, Sergey I.; Boltasseva, Alexandra; Søndergaard, Thomas

    2005-01-01

    -size thickness variations result in the pronounced band gap effect, and obtain very good agreement between measured and simulated (transmission and reflection) spectra. This effect is exploited to realize a compact wavelength add-drop filter with the bandwidth of -20 nm centered at 1550 nm. The possibilities...... of achieving a full bandgap (in the surface plane) for LR-SPPs are also discussed....

  2. Automating Energy Bandgap Measurements in Semiconductors Using LabVIEW

    Science.gov (United States)

    Garg, Amit; Sharma, Reena; Dhingra, Vishal

    2010-01-01

    In this paper, we report the development of an automated system for energy bandgap and resistivity measurement of a semiconductor sample using Four-Probe method for use in the undergraduate laboratory of Physics and Electronics students. The automated data acquisition and analysis system has been developed using National Instruments USB-6008 DAQ…

  3. Bandgap Opening in Graphene Induced by Patterned Hydrogen Adsorption

    DEFF Research Database (Denmark)

    Balog, Richard; Jørgensen, Bjarke; Nilsson, Louis

    2010-01-01

    fermions, and graphene shows ballistic charge transport, turning it into an ideal material for circuit fabrication. However, graphene lacks a bandgap around the Fermi level, which is the defining concept for semiconductor materials and essential for controlling the conductivity by electronic means. Theory...

  4. Design of photonic bandgap fibers by topology optimization

    DEFF Research Database (Denmark)

    Dühring, Maria Bayard; Sigmund, Ole; Feurer, Thomas

    2010-01-01

    A method based on topology optimization is presented to design the cross section of hollow-core photonic bandgap fibers for minimizing energy loss by material absorption. The optical problem is modeled by the timeharmonic wave equation and solved with the finite element program Comsol Multiphysics...

  5. Electrically controllable liquid crystal photonic bandgap fiber with dual-frequency control

    DEFF Research Database (Denmark)

    Scolari, Lara; Alkeskjold, Thomas Tanggaard; Riishede, Jesper

    2005-01-01

    We present an electrically tunable liquid crystal photonic bandgap fiber device based on a dual frequency liquid crystal with pre-tilted molecules that allows the bandgaps to be continuously tuned. The frequency dependent behavior of the liquid crystal enables active shifting of the bandgaps toward...

  6. Very Small Bandgap π-Conjugated Polymers with Extended Thienoquinoids.

    Science.gov (United States)

    Kawabata, Kohsuke; Saito, Masahiko; Osaka, Itaru; Takimiya, Kazuo

    2016-06-22

    The introduction of quinoidal character to π-conjugated polymers is one of the effective approaches to reducing the bandgap. Here we synthesized new π-conjugated polymers (PBTD4T and PBDTD4T) incorporating thienoquinoids 2,2'-bithiophene-5,5'-dione (BTD) and benzo[1,2-b:4,5-b']dithiophene-2,6-dione (BDTD) as strong electron-deficient (acceptor) units. PBTD4T showed a deep LUMO energy level of -3.77 eV and a small bandgap of 1.28 eV, which are similar to those of the analog using thieno[3,2-b]thiophene-2,5-dione (TTD) (PTTD4T). PBDTD4T had a much deeper LUMO energy level of -4.04 eV and a significantly smaller bandgap of 0.88 eV compared to those of the other two polymers. Interestingly, PBDTD4T showed high transparency in the visible region. The very small bandgap of PBDTD4T can be rationalized by the enhanced contribution of the resonance backbone structure in which the p-benzoquinodimethane skeleton in the BDTD unit plays a crucial role. PBTD4T and PBDTD4T exhibited ambipolar charge transport with more balanced mobilities between the hole and the electron than PTTD4T. We believe that the very small bandgap, i.e., the high near-infrared activity, as well as the well-balanced ambipolar property of the π-conjugated polymers based on these units would be of particular interest in the fabrication of next-generation organic devices.

  7. Optimal design of tunable phononic bandgap plates under equibiaxial stretch

    Science.gov (United States)

    Hedayatrasa, Saeid; Abhary, Kazem; Uddin, M. S.; Guest, James K.

    2016-05-01

    Design and application of phononic crystal (PhCr) acoustic metamaterials has been a topic with tremendous growth of interest in the last decade due to their promising capabilities to manipulate acoustic and elastodynamic waves. Phononic controllability of waves through a particular PhCr is limited only to the spectrums located within its fixed bandgap frequency. Hence the ability to tune a PhCr is desired to add functionality over its variable bandgap frequency or for switchability. Deformation induced bandgap tunability of elastomeric PhCr solids and plates with prescribed topology have been studied by other researchers. Principally the internal stress state and distorted geometry of a deformed phononic crystal plate (PhP) changes its effective stiffness and leads to deformation induced tunability of resultant modal band structure. Thus the microstructural topology of a PhP can be altered so that specific tunability features are met through prescribed deformation. In the present study novel tunable PhPs of this kind with optimized bandgap efficiency-tunability of guided waves are computationally explored and evaluated. Low loss transmission of guided waves throughout thin walled structures makes them ideal for fabrication of low loss ultrasound devices and structural health monitoring purposes. Various tunability targets are defined to enhance or degrade complete bandgaps of plate waves through macroscopic tensile deformation. Elastomeric hyperelastic material is considered which enables recoverable micromechanical deformation under tuning finite stretch. Phononic tunability through stable deformation of phononic lattice is specifically required and so any topology showing buckling instability under assumed deformation is disregarded. Nondominated sorting genetic algorithm (GA) NSGA-II is adopted for evolutionary multiobjective topology optimization of hypothesized tunable PhP with square symmetric unit-cell and relevant topologies are analyzed through finite

  8. A narrow-bandgap benzobisthiadiazole derivative with high near-infrared photothermal conversion efficiency and robust photostability for cancer therapy.

    Science.gov (United States)

    Huang, Shuo; Kannadorai, Ravi Kumar; Chen, Yuan; Liu, Quan; Wang, Mingfeng

    2015-03-11

    Photothermal therapy has emerged as a promising tool for treatment of diseases such as cancers. Previous photothermal agents have been largely limited to inorganic nanomaterials and conductive polymers that are barely biodegradable, thus raising issues of long-term toxicity for clinical applications. Here we report a new photothermal agent based on colloidal nanoparticles formed by a small-molecular dye, benzo[1,2-c;4,5-c']bis[1,2,5]thiadiazole-4,7-bis(5-(2-ethylhexyl)thiophene). These nanoparticles showed strong near-infrared absorption, robust photostability and high therapeutic efficiency for photothermal treatment of cancer cells.

  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 grown in microgravity, because convection causes crystalline defects by mising hot and cold fluids and generating temperature fluctuations in them.

  10. Benzo[1,2-b:4,5-b′]Dithiophene-6,7-Difluoroquinoxaline Small Molecule Donors with >8% BHJ Solar Cell Efficiency

    KAUST Repository

    Liang, Ru-Ze

    2017-07-14

    Solution-processable small molecule (SM) donors are promising alternatives to their polymer counterparts in bulk-heterojunction (BHJ) solar cells. While SM donors with favorable spectral absorption, self-assembly patterns, optimum thin-film morphologies, and high carrier mobilities in optimized donor–acceptor blends are required to further BHJ device efficiencies, material structure governs each one of those attributes. As a result, the rational design of SM donors with gradually improved BHJ solar cell efficiencies must concurrently address: (i) bandgap tuning and optimization of spectral absorption (inherent to the SM main chain) and (ii) pendant-group substitution promoting structural order and mediating morphological effects. In this paper, the rational pendant-group substitution in benzo[1,2-b:4,5-b′]dithiophene–6,7-difluoroquinoxaline SMs is shown to be an effective approach to narrowing the optical gap (Eopt) of the SM donors (SM1 and SM2), without altering their propensity to order and form favorable thin-film BHJ morphologies with PC71BM. Systematic device examinations show that power conversion efficiencies >8% and open-circuit voltages (VOC) nearing 1 V can be achieved with the narrow-gap SM donor analog (SM2, Eopt = 1.6 eV) and that charge transport in optimized BHJ solar cells proceeds with minimal, nearly trap-free recombination. Detailed device simulations, light intensity dependence, and transient photocurrent analyses emphasize how carrier recombination impacts BHJ device performance upon optimization of active layer thickness and morphology.

  11. Kinetic narrowing of size distribution

    Science.gov (United States)

    Dubrovskii, V. G.

    2016-05-01

    We present a model that reveals an interesting possibility for narrowing the size distribution of nanostructures when the deterministic growth rate changes its sign from positive to negative at a certain stationary size. Such a behavior occurs in self-catalyzed one-dimensional III-V nanowires and more generally whenever a negative "adsorption-desorption" term in the growth rate is compensated by a positive "diffusion flux." By asymptotically solving the Fokker-Planck equation, we derive an explicit representation for the size distribution that describes either Poissonian broadening or self-regulated narrowing depending on the parameters. We show how the fluctuation-induced spreading of the size distribution can be completely suppressed in systems with size self-stabilization. These results can be used for obtaining size-uniform ensembles of different nanostructures.

  12. "Credit Markets and Narrow Banking"

    OpenAIRE

    Ronnie Phillips

    1992-01-01

    Maurice Allais's view that the credit created by fractional reserve banking is equivalent to counterfeiting has led him to recommend the separation of the depository and lending functions of banks. This proposal has recently been reintroduced by James Tobin and others under the term "narrow banking." Proponents cite the potential for enhanced safety of the payments mechanism and the elimination of costs associated with the preses system of Federal deposit insurance. This plan resembles the "1...

  13. High-Performance Non-Fullerene Polymer Solar Cells Based on a Pair of Donor-Acceptor Materials with Complementary Absorption Properties.

    Science.gov (United States)

    Lin, Haoran; Chen, Shangshang; Li, Zhengke; Lai, Joshua Yuk Lin; Yang, Guofang; McAfee, Terry; Jiang, Kui; Li, Yunke; Liu, Yuhang; Hu, Huawei; Zhao, Jingbo; Ma, Wei; Ade, Harald; Yan, He

    2015-12-01

    A 7.3% efficiency non-fullerene polymer solar cell is realized by combining a large-bandgap polymer PffT2-FTAZ-2DT with a small-bandgap acceptor IEIC. The complementary absorption of donor polymer and small-molecule acceptor is responsible for the high-performance of the solar-cell device. This work provides important guidance to improve the performance of non-fullerene polymer solar cells.

  14. Simulation Evidence of Hexagonal‐to‐Tetragonal ZnSe Structure Transition: A Monolayer Material with a Wide‐Range Tunable Direct Bandgap

    Science.gov (United States)

    Li, Lei; Li, Pengfei; Lu, Ning; Dai, Jun

    2015-01-01

    2D material with tunable direct bandgap in the intermediate region (i.e., ≈2–3 eV) is key to the achievement of high efficiency in visible‐light optical devices. Herein, a simulation evidence of structure transition of monolayer ZnSe from the experimental pseudohexagonal structure to the tetragonal structure (t‐ZnSe) under lateral pressure is shown, suggesting a possible fabrication route to achieve the t‐ZnSe monolayer. The as‐produced t‐ZnSe monolayer exhibits highly tunable bandgap under the biaxial strains, allowing strain engineering of t‐ZnSe's bandgap over a wide range of 2–3 eV. Importantly, even under the biaxial strain up to 7%, the t‐ZnSe monolayer still keeps its direct‐gap property in the desirable range of 2.40–3.17 eV (corresponding to wavelength of green light to ultraviolet). The wide‐range tunability of direct bandgap appears to be a unique property of the t‐ZnSe monolayer, suggesting its potential application as a light‐emitting 2D material in red–green–blue light emission diodes or as complementary light‐absorption material in the blue–yellow region for multijunction solar cells. The straddling of the band edge of the t‐ZnSe monolayer over the redox potential of water splitting reaction also points to its plausible application for visible‐light‐driven water splitting. PMID:27774379

  15. Simulation Evidence of Hexagonal-to-Tetragonal ZnSe Structure Transition: A Monolayer Material with a Wide-Range Tunable Direct Bandgap.

    Science.gov (United States)

    Li, Lei; Li, Pengfei; Lu, Ning; Dai, Jun; Zeng, Xiao Cheng

    2015-12-01

    2D material with tunable direct bandgap in the intermediate region (i.e., ≈2-3 eV) is key to the achievement of high efficiency in visible-light optical devices. Herein, a simulation evidence of structure transition of monolayer ZnSe from the experimental pseudohexagonal structure to the tetragonal structure (t-ZnSe) under lateral pressure is shown, suggesting a possible fabrication route to achieve the t-ZnSe monolayer. The as-produced t-ZnSe monolayer exhibits highly tunable bandgap under the biaxial strains, allowing strain engineering of t-ZnSe's bandgap over a wide range of 2-3 eV. Importantly, even under the biaxial strain up to 7%, the t-ZnSe monolayer still keeps its direct-gap property in the desirable range of 2.40-3.17 eV (corresponding to wavelength of green light to ultraviolet). The wide-range tunability of direct bandgap appears to be a unique property of the t-ZnSe monolayer, suggesting its potential application as a light-emitting 2D material in red-green-blue light emission diodes or as complementary light-absorption material in the blue-yellow region for multijunction solar cells. The straddling of the band edge of the t-ZnSe monolayer over the redox potential of water splitting reaction also points to its plausible application for visible-light-driven water splitting.

  16. Towards efficient solar-to-hydrogen conversion: Fundamentals and recent progress in copper-based chalcogenide photocathodes

    Directory of Open Access Journals (Sweden)

    Chen Yubin

    2016-09-01

    Full Text Available Photoelectrochemical (PEC water splitting for hydrogen generation has been considered as a promising route to convert and store solar energy into chemical fuels. In terms of its large-scale application, seeking semiconductor photoelectrodes with high efficiency and good stability should be essential. Although an enormous number of materials have been explored for solar water splitting in the last several decades, challenges still remain for the practical application. P-type copper-based chalcogenides, such as Cu(In, GaSe2 and Cu2ZnSnS4, have shown impressive performance in photovoltaics due to narrow bandgaps, high absorption coefficients, and good carrier transport properties. The obtained high efficiencies in photovoltaics have promoted the utilization of these materials into the field of PEC water splitting. A comprehensive review on copper-based chalcogenides for solar-to-hydrogen conversion would help advance the research in this expanding area. This review will cover the physicochemical properties of copper-based chalco-genides, developments of various photocathodes, strategies to enhance the PEC activity and stability, introductions of tandem PEC cells, and finally, prospects on their potential for the practical solar-to-hydrogen conversion. We believe this review article can provide some insights of fundamentals and applications of copper-based chalco-genide thin films for PEC water splitting.

  17. Towards efficient solar-to-hydrogen conversion: Fundamentals and recent progress in copper-based chalcogenide photocathodes

    Science.gov (United States)

    Chen, Yubin; Feng, Xiaoyang; Liu, Maochang; Su, Jinzhan; Shen, Shaohua

    2016-09-01

    Photoelectrochemical (PEC) water splitting for hydrogen generation has been considered as a promising route to convert and store solar energy into chemical fuels. In terms of its large-scale application, seeking semiconductor photoelectrodes with high efficiency and good stability should be essential. Although an enormous number of materials have been explored for solar water splitting in the last several decades, challenges still remain for the practical application. P-type copper-based chalcogenides, such as Cu(In, Ga)Se2 and Cu2ZnSnS4, have shown impressive performance in photovoltaics due to narrow bandgaps, high absorption coefficients, and good carrier transport properties. The obtained high efficiencies in photovoltaics have promoted the utilization of these materials into the field of PEC water splitting. A comprehensive review on copper-based chalcogenides for solar-to-hydrogen conversion would help advance the research in this expanding area. This review will cover the physicochemical properties of copper-based chalco-genides, developments of various photocathodes, strategies to enhance the PEC activity and stability, introductions of tandem PEC cells, and finally, prospects on their potential for the practical solar-to-hydrogen conversion. We believe this review article can provide some insights of fundamentals and applications of copper-based chalco-genide thin films for PEC water splitting.

  18. Energy level alignment in TiO2/metal sulfide/polymer interfaces for solar cell applications.

    Science.gov (United States)

    Lindblad, Rebecka; Cappel, Ute B; O'Mahony, Flannan T F; Siegbahn, Hans; Johansson, Erik M J; Haque, Saif A; Rensmo, Håkan

    2014-08-28

    Semiconductor sensitized solar cell interfaces have been studied with photoelectron spectroscopy to understand the interfacial electronic structures. In particular, the experimental energy level alignment has been determined for complete TiO2/metal sulfide/polymer interfaces. For the metal sulfides CdS, Sb2S3 and Bi2S3 deposited from single source metal xanthate precursors, it was shown that both driving forces for electron injection into TiO2 and hole transfer to the polymer decrease for narrower bandgaps. The energy level alignment results were used in the discussion of the function of solar cells with the same metal sulfides as light absorbers. For example Sb2S3 showed the most favourable energy level alignment with 0.3 eV driving force for electron injection and 0.4 eV driving force for hole transfer and also the most efficient solar cells due to high photocurrent generation. The energy level alignment of the TiO2/Bi2S3 interface on the other hand showed no driving force for electron injection to TiO2, and the performance of the corresponding solar cell was very low.

  19. Influence of absorber doping in a-SiC:H/a-Si:H/a-SiGe:H solar cells

    Science.gov (United States)

    Nawaz, Muhammad; Ahmad, Ashfaq

    2012-04-01

    This work deals with the design evaluation and influence of absorber doping for a-Si:H/a-SiC:H/a-SiGe:H based thin-film solar cells using a two-dimensional computer aided design (TCAD) tool. Various physical parameters of the layered structure, such as doping and thickness of the absorber layer, have been studied. For reliable device simulation with realistic predictability, the device performance is evaluated by implementing necessary models (e.g., surface recombinations, thermionic field emission tunneling model for carrier transport at the heterojunction, Schokley—Read Hall recombination model, Auger recombination model, bandgap narrowing effects, doping and temperature dependent mobility model and using Fermi—Dirac statistics). A single absorber with a graded design gives an efficiency of 10.1% for 800 nm thick multiband absorption. Similarly, a tandem design shows an efficiency of 10.4% with a total absorber of thickness of 800 nm at a bandgap of 1.75 eV and 1.0 eV for the top a-Si and bottom a-SiGe component cells. A moderate n-doping in the absorber helps to improve the efficiency while p doping in the absorber degrades efficiency due to a decrease in the VOC (and fill factor) of the device.

  20. Influence of absorber doping in a-SiC:H/a-Si:H/a-SiGe:H solar cells

    Institute of Scientific and Technical Information of China (English)

    Muhammad Nawaz; Ashfaq Ahmad

    2012-01-01

    This work deals with the design evaluation and influence of absorber doping for a-Si:H/a-SiC:H/a-SiGe:H based thin-film solar cells using a two-dimensional computer aided design (TCAD) tool.Various physical parameters of the layered structure,such as doping and thickness of the absorber layer,have been studied.For reliable device simulation with realistic predictability,the device performance is evaluated by implementing necessary models (e.g.,surface recombinations,thermionic field emission tunneling model for carrier transport at the heterojunction,Schokley-Read Hall recombination model,Auger recombination model,bandgap narrowing effects,doping and temperature dependent mobility model and using Fermi-Dirac statistics).A single absorber with a graded design gives an efficiency of 10.1% for 800 nm thick multiband absorption.Similarly,a tandem design shows an efficiency of 10.4% with a total absorber of thickness of 800 nm at a bandgap of 1.75 eV and 1.0 eV for the top a-Si and bottom a-SiGe component cells.A moderate n-doping in the absorber helps to improve the efficiency while p doping in the absorber degrades efficiency due to a decrease in the Voc (and fill factor) of the device.

  1. Water Will Be the Coal of the Future—The Untamed Dream of Jules Verne for a Solar Fuel

    Directory of Open Access Journals (Sweden)

    Vladimir K. Ryabchuk

    2016-11-01

    Full Text Available This article evokes the futuristic visions of two giants, one a writer, Jules Verne, who foresaw water as the coal of the future, and the other a scientist, Giacomo Ciamician, who foresaw the utilization of solar energy as an energy source with which to drive photochemical and photocatalytic reactions for the betterment of mankind. Specifically, we examine briefly the early work of the 1960s and 1970s on the photosplitting of free water and water adsorbed on solid supports, based mostly on metal oxides, from which both hydrogen and oxygen evolve in the expected stoichiometric ratio of 2 to 1. The two oil crises of the 1970s (1973 and 1979 spurred the interest of researchers from various disciplines (photochemistry, photo-catalysis and photoelectrochemistry in search of a Holy Grail photocatalyst, process, or strategy to achieve efficient water splitting so as to provide an energy source alternative to fossil fuels. Some approaches to the photosplitting of water adsorbed on solid insulators (high bandgap materials; Ebg ≥ 5 eV and semiconductor photocatalysts (metal oxides are described from which we deduce that metal oxides with bandgap energies around 5 eV (e.g., ZrO2 are more promising materials to achieve significant water splitting on the basis of quantum yields than narrower bandgap photocatalysts (e.g., TiO2; Ebg ≈ 3.0–3.2 eV, which tend to be relatively inactive by comparison. Although proof of concept of the photosplitting of water has been demonstrated repeatedly in the last four decades, much remains to be done to find the Holy Grail photocatalyst and/or strategy to achieve significant yields of hydrogen.

  2. Water Will Be the Coal of the Future-The Untamed Dream of Jules Verne for a Solar Fuel.

    Science.gov (United States)

    Ryabchuk, Vladimir K; Kuznetsov, Vyacheslav N; Emeline, Alexei V; Artem'ev, Yurii M; Kataeva, Galina V; Horikoshi, Satoshi; Serpone, Nick

    2016-11-29

    This article evokes the futuristic visions of two giants, one a writer, Jules Verne, who foresaw water as the coal of the future, and the other a scientist, Giacomo Ciamician, who foresaw the utilization of solar energy as an energy source with which to drive photochemical and photocatalytic reactions for the betterment of mankind. Specifically, we examine briefly the early work of the 1960s and 1970s on the photosplitting of free water and water adsorbed on solid supports, based mostly on metal oxides, from which both hydrogen and oxygen evolve in the expected stoichiometric ratio of 2 to 1. The two oil crises of the 1970s (1973 and 1979) spurred the interest of researchers from various disciplines (photochemistry, photo-catalysis and photoelectrochemistry) in search of a Holy Grail photocatalyst, process, or strategy to achieve efficient water splitting so as to provide an energy source alternative to fossil fuels. Some approaches to the photosplitting of water adsorbed on solid insulators (high bandgap materials; Ebg ≥ 5 eV) and semiconductor photocatalysts (metal oxides) are described from which we deduce that metal oxides with bandgap energies around 5 eV (e.g., ZrO₂) are more promising materials to achieve significant water splitting on the basis of quantum yields than narrower bandgap photocatalysts (e.g., TiO₂; Ebg ≈ 3.0-3.2 eV), which tend to be relatively inactive by comparison. Although proof of concept of the photosplitting of water has been demonstrated repeatedly in the last four decades, much remains to be done to find the Holy Grail photocatalyst and/or strategy to achieve significant yields of hydrogen.

  3. Transient absorption spectroscopy studies on polythiophene-fullerene bulk heterojunction organic blend films sensitized with a low-bandgap polymer.

    Science.gov (United States)

    Löslein, Heiko; Ameri, Tayebeh; Matt, Gebhard J; Koppe, Markus; Egelhaaf, Hans J; Troeger, Anna; Sgobba, Vito; Guldi, Dirk M; Brabec, Christoph J

    2013-07-12

    Recently, the concept of near-infrared sensitization is successfully employed to increase the light harvesting in large-bandgap polymer-based solar cells. To gain deeper insights into the operation mechanism of ternary organic solar cells, a comprehensive understanding of charge transfer-charge transport in ternary blends is a necessity. Herein, P3HT:PCPDTBT:PCBM ternary blend films are investigated by transient absorption spectroscopy. Hole transfer from PCPDTBT-positive polarons to P3HT in the P3HT:PCPDTBT:PCBM 0.9:0.1:1 blend film can be visualized. This process evolves within 140 ps and is discussed with respect to the proposed charge-generation mechanisms.

  4. Narrowing SWNT diameter distribution using size-separated ferritin-based Fe catalysts.

    Science.gov (United States)

    Durrer, Lukas; Greenwald, Jason; Helbling, Thomas; Muoth, Matthias; Riek, Roland; Hierold, Christofer

    2009-09-02

    Sensors and devices made from single-walled carbon nanotubes (SWNTs) are most often electrically probed through metal leads contacting the semiconducting SWNTs (s-SWNTs). Contact barriers in general and Schottky barriers (SBs) in particular are usually obtained at a metal-semiconductor interface. The unique one-dimensional structure (1D) of SWNTs allows tailoring of the SB heights through the contact metal type and the size of the s-SWNT bandgap. A large workfunction reduces the SB height (e.g. using Pd as the metal contact material). The bandgap of an SWNT is inversely proportional to its diameter. Ohmic contacts--the preferable choice--are achieved for s-SWNTs with diameters greater than 2 nm on Pd metal leads. SWNT device reproducibility, on the other hand, requires a narrow distribution of the SWNT diameters. Here, we present a method to fabricate SWNTs with a large and adjustable mean diameter (1.9-2.4 nm) and very narrow diameter distribution (+/- 0.27 nm at mean diameter 1.9 nm). The results are achieved through a size separation of the ferritin catalyst particles by sedimentation velocity centrifugation prior to their use in the chemical vapor deposition (CVD) formation of SWNTs.

  5. Narrowing SWNT diameter distribution using size-separated ferritin-based Fe catalysts

    Energy Technology Data Exchange (ETDEWEB)

    Durrer, Lukas; Helbling, Thomas; Muoth, Matthias; Hierold, Christofer [Micro and Nanosystems, Department of Mechanical and Process Engineering, ETH Zuerich, CH-8092 Zurich (Switzerland); Greenwald, Jason; Riek, Roland, E-mail: lukas.durrer@micro.mavt.ethz.c [Laboratory of Physical Chemistry, ETH Zurich, CH-8093 Zuerich (Switzerland)

    2009-09-02

    Sensors and devices made from single-walled carbon nanotubes (SWNTs) are most often electrically probed through metal leads contacting the semiconducting SWNTs (s-SWNTs). Contact barriers in general and Schottky barriers (SBs) in particular are usually obtained at a metal-semiconductor interface. The unique one-dimensional structure (1D) of SWNTs allows tailoring of the SB heights through the contact metal type and the size of the s-SWNT bandgap. A large workfunction reduces the SB height (e.g. using Pd as the metal contact material). The bandgap of an SWNT is inversely proportional to its diameter. Ohmic contacts-the preferable choice-are achieved for s-SWNTs with diameters greater than 2 nm on Pd metal leads. SWNT device reproducibility, on the other hand, requires a narrow distribution of the SWNT diameters. Here, we present a method to fabricate SWNTs with a large and adjustable mean diameter (1.9-2.4 nm) and very narrow diameter distribution ({+-} 0.27 nm at mean diameter 1.9 nm). The results are achieved through a size separation of the ferritin catalyst particles by sedimentation velocity centrifugation prior to their use in the chemical vapor deposition (CVD) formation of SWNTs.

  6. Composition/bandgap selective dry photochemical etching of semiconductor materials

    Energy Technology Data Exchange (ETDEWEB)

    Ashby, C.I.H.; Dishman, J.L.

    1985-10-11

    Disclosed is a method of selectively photochemically dry etching a first semiconductor material of a given composition and direct bandgap Eg/sub 1/ in the presence of a second semiconductor material of a different composition and direct bandgap Eg/sub 2/, wherein Eg/sub 2/ > Eg/sub 1/, said second semiconductor material substantially not being etched during said method. The method comprises subjecting both materials to the same photon flux and to the same gaseous etchant under conditions where said etchant would be ineffective for chemical etching of either material were the photons not present, said photons being of an energy greater than Eg/sub 1/ but less than Eg/sub 2/, whereby said first semiconductor material is photochemically etched and said second material is substantially not etched.

  7. Composition/bandgap selective dry photochemical etching of semiconductor materials

    Energy Technology Data Exchange (ETDEWEB)

    Ashby, Carol I. H. (Edgewood, NM); Dishman, James L. (Albuquerque, NM)

    1987-01-01

    A method of selectively photochemically dry etching a first semiconductor material of a given composition and direct bandgap Eg.sub.1 in the presence of a second semiconductor material of a different composition and direct bandgap Eg.sub.2, wherein Eg.sub.2 >Eg.sub.1, said second semiconductor material substantially not being etched during said method, comprises subjecting both materials to the same photon flux and to the same gaseous etchant under conditions where said etchant would be ineffective for chemical etching of either material were the photons not present, said photons being of an energy greater than Eg.sub.1 but less than Eg.sub.2, whereby said first semiconductor material is photochemically etched and said second material is substantially not etched.

  8. Composition/bandgap selective dry photochemical etching of semiconductor materials

    Energy Technology Data Exchange (ETDEWEB)

    Ashby, C.I.H.; Dishman, J.L.

    1987-03-10

    A method is described of selectively photochemically dry etching a first semiconductor material of a given composition and direct bandgap E/sub g1/ in the presence of a second semiconductor material of a different composition and direct bandgap E/sub g2/, wherein E/sub g2/>E/sub g1/. The second semiconductor material is not substantially etched during the method, comprising subjecting both materials to the same photon flux and to the same gaseous etchant under conditions where the etchant would be ineffective for chemical etching of either material where the photons are not present, the photons being of an energy greater than E/sub g1/ but less than E/sub g2/, whereby the first semiconductor material is photochemically etched and the second material is substantially not etched.

  9. High extinction ratio bandgap of photonic crystals in LNOI wafer

    Science.gov (United States)

    Zhang, Shao-Mei; Cai, Lu-Tong; Jiang, Yun-Peng; Jiao, Yang

    2017-02-01

    A high-extinction-ratio bandgap of air-bridge photonic crystal slab, in the near infrared, is reported. These structures were patterned in single-crystalline LiNbO3 film bonded to SiO2/LiNbO3 substrate by focused ion beam. To improve the vertical confinement of light, the SiO2 layer was removed by 3.6% HF acid. Compared with photonic crystals sandwiched between SiO2 and air, the structures suspending in air own a robust photonic bandgap and high transmission efficiency at valence band region. The measured results are in good agreement with numerically computed transmission spectra by finite-difference time-domain method. The air-bridge photonic crystal waveguides were formed by removing one line holes. We reveal experimentally the guiding characteristics and calculate the theoretical results for photonic crystal waveguides in LiNbO3 film.

  10. Quantum electrodynamics near a photonic band-gap

    Science.gov (United States)

    Liu, Yanbing; Houck, Andrew

    Quantum electrodynamics predicts the localization of light around an atom in photonic band-gap (PBG) medium or photonic crystal. Here we report the first experimental realization of the strong coupling between a single artificial atom and an one dimensional PBG medium using superconducting circuits. In the photonic transport measurement, we observe an anomalous Lamb shift and a large band-edge avoided crossing when the artificial atom frequency is tuned across the band-edge. The persistent peak within the band-gap indicates the single photon bound state. Furthermore, we study the resonance fluorescence of this bound state, again demonstrating the breakdown of the Born-Markov approximation near the band-edge. This novel architecture can be directly generalized to study many-body quantum electrodynamics and to construct more complicated spin chain models.

  11. Low Loss Plastic Terahertz Photonic Band-Gap Fibres

    Institute of Scientific and Technical Information of China (English)

    GENG You-Fu; TAN Xiao-Ling; ZHONG Kai; WANG Peng; YAO Jian-Quan

    2008-01-01

    We report a numerical investigation on terahertz wave propagation in plastic photonic band-gap fibres which are characterized by a 19-unit-cell air core and hexagonal air holes with rounded corners in cladding. Using the finite element method, the leakage loss and absorption loss are calculated and the transmission properties are analysed.The lowest loss of 0.268 dB/m is obtained. Numerical results show that the fibres could liberate the constraints of background materials beyond the transparency region in terahertz wave band, and efficiently minimize the effect of absorption by background materials, which present great advantage of plastic photonic band-gap fibres in long distance terahertz delivery.

  12. Experimental Methods for Implementing Graphene Contacts to Finite Bandgap Semiconductors

    DEFF Research Database (Denmark)

    Meyer-Holdt, Jakob

    for molecular electronics with parallel CVD graphene bottom electrodes with SiO2 passivation was successfully fabricated and electronically characterized. A functioning Carbon Burger was not achieved. Along the work on the Carbon Burger, the scope was broadened and focus was put on implementing graphene......Present Ph.D. thesis describes my work on implanting graphene as electrical contact to finite bandgap semiconductors. Different transistor architectures, types of graphene and finite bandgap semiconductors have been employed. The device planned from the beginning of my Ph.D. fellowship...... was a graphene-C60 monolayergraphene vertical transistor named the Carbon Burger. The fabrication of such device proved increasingly difficult to achieve and many experimental methods to handle graphene were implemented and improved in attempt to fabricate the Carbon Burger. In the end, a device platform...

  13. Omnidirectional bandgaps in Fibonacci quasicrystals containing single-negative materials.

    Science.gov (United States)

    Deng, Xin-Hua; Liu, Jiang-Tao; Huang, Jie-Hui; Zou, Liner; Liu, Nian-Hua

    2010-02-10

    The band structure and bandgaps of one-dimensional Fibonacci quasicrystals composed of epsilon-negative materials and mu-negative materials are studied. We show that an omnidirectional bandgap (OBG) exists in the Fibonacci structure. In contrast to the Bragg gaps, such an OBG is insensitive to the incident angle and the polarization of light, and the width and location of the OBG cease to change with increasing Fibonacci order, but vary with the thickness ratio of both components, and the OBG closes when the thickness ratio is equal to the golden ratio. Moreover, the general formulations of the higher and lower band edges of the OBG are obtained by the effective medium theory. These results could lead to further applications of Fibonacci structures.

  14. Comparison of Wide-Bandgap Semiconductors for Power Electronics Applications

    Energy Technology Data Exchange (ETDEWEB)

    Ozpineci, B.

    2004-01-02

    Recent developmental advances have allowed silicon (Si) semiconductor technology to approach the theoretical limits of the Si material; however, power device requirements for many applications are at a point that the present Si-based power devices cannot handle. The requirements include higher blocking voltages, switching frequencies, efficiency, and reliability. To overcome these limitations, new semiconductor materials for power device applications are needed. For high power requirements, wide-bandgap semiconductors like silicon carbide (SiC), gallium nitride (GaN), and diamond, with their superior electrical properties, are likely candidates to replace Si in the near future. This report compares wide-bandgap semiconductors with respect to their promise and applicability for power applications and predicts the future of power device semiconductor materials.

  15. Design techniques for superposition of acoustic bandgaps using fractal geometries

    CERN Document Server

    Castiñeira-Ibáñez, S; Sánchez-Pérez, J V; Garcia-Raffi, L M

    2010-01-01

    Research into properties of heterogeneous artificial materials, consisting of arrangements of rigid scatterers embedded in a medium with different elastic properties, has been intense throughout last two decades. The capability to prevent the transmission of waves in predetermined bands of frequencies -called bandgaps- becomes one of the most interesting properties of these systems, and leads to the possibility of designing devices to control wave propagation. The underlying physical mechanism is destructive Bragg interference. Here we show a technique that enables the creation of a wide bandgap in these materials, based on fractal geometries. We have focused our work in the acoustic case where these materials are called Phononic/Sonic Crystals (SC) but, the technique could be applied any types of crystals and wave types in ranges of frequencies where the physics of the process is linear.

  16. Band structure of germanium carbides for direct bandgap silicon photonics

    Science.gov (United States)

    Stephenson, C. A.; O'Brien, W. A.; Penninger, M. W.; Schneider, W. F.; Gillett-Kunnath, M.; Zajicek, J.; Yu, K. M.; Kudrawiec, R.; Stillwell, R. A.; Wistey, M. A.

    2016-08-01

    Compact optical interconnects require efficient lasers and modulators compatible with silicon. Ab initio modeling of Ge1-xCx (x = 0.78%) using density functional theory with HSE06 hybrid functionals predicts a splitting of the conduction band at Γ and a strongly direct bandgap, consistent with band anticrossing. Photoreflectance of Ge0.998C0.002 shows a bandgap reduction supporting these results. Growth of Ge0.998C0.002 using tetrakis(germyl)methane as the C source shows no signs of C-C bonds, C clusters, or extended defects, suggesting highly substitutional incorporation of C. Optical gain and modulation are predicted to rival III-V materials due to a larger electron population in the direct valley, reduced intervalley scattering, suppressed Auger recombination, and increased overlap integral for a stronger fundamental optical transition.

  17. Treating temperature effect on bandgap in polymer opal photonic crystals

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    The optical reflective spectra and microstruc- tures of polystyrene opal photonic crystals treated with dif- ferent temperatures have been investigated. With tempera- ture increasing, the polystyrene spheres in opal structure transform to dodecahedrons, and the peak of reflective spec- trum moves to shorter wavelength. The experiment result testifies the effect of the effective refractive index and the filling ratio to the bandgap position, and it corresponds to the theoretical simulative result.

  18. Feasibility of detecting single atoms using photonic bandgap cavities

    OpenAIRE

    Lev, Benjamin; Srinivasan, Kartik; Barclay, Paul; Painter, Oskar; Mabuchi, Hideo

    2004-01-01

    We propose an atom-cavity chip that combines laser cooling and trapping of neutral atoms with magnetic microtraps and waveguides to deliver a cold atom to the mode of a fiber taper coupled photonic bandgap (PBG) cavity. The feasibility of this device for detecting single atoms is analyzed using both a semi-classical treatment and an unconditional master equation approach. Single-atom detection seems achievable in an initial experiment involving the non-deterministic delivery of weakly trapped...

  19. Driven tracers in narrow channels

    Science.gov (United States)

    Cividini, J.; Mukamel, D.; Posch, H. A.

    2017-01-01

    Steady-state properties of a driven tracer moving in a narrow two-dimensional (2D) channel of quiescent medium are studied. The tracer drives the system out of equilibrium, perturbs the density and pressure fields, and gives the bath particles a nonzero average velocity, creating a current in the channel. Three models in which the confining effect of the channel is probed are analyzed and compared in this study: the first is the simple symmetric exclusion process (SSEP), for which the stationary density profile and the pressure on the walls in the frame of the tracer are computed. We show that the tracer acts like a dipolar source in an average velocity field. The spatial structure of this 2D strip is then simplified to a one-dimensional (1D) SSEP, in which exchanges of position between the tracer and the bath particles are allowed. Using a combination of mean-field theory and exact solution in the limit where no exchange is allowed gives good predictions of the velocity of the tracer and the density field. Finally, we show that results obtained for the 1D SSEP with exchanges also apply to a gas of overdamped hard disks in a narrow channel. The correspondence between the parameters of the SSEP and of the gas of hard disks is systematic and follows from simple intuitive arguments. Our analytical results are checked numerically.

  20. Spectral Narrowing in Semiconductor Microcavities

    Science.gov (United States)

    La Rocca, G. C.; Bassani, F.; Agranovich, V. M.

    1998-03-01

    The notion of in-plane motional narrowing of cavity polariton (CP) lines has been recently considered ( D.M. Whittaker et al.), Phys. Rev. Lett. 77, 4792 (1996); V. Savona et al.. Phys. Rev. Lett. 78, 4470 (1997). We point out that, in the presence of N>1 resonating quantum wells (QWs), the exciton component in a CP is coherently delocalized over all the individual QWs. Besides the two CP branches, also a dark exciton branch is present given by N-1 states similarly delocalized, but orthogonal to the cavity photon mode. If the QW disorder potential is weak compared to the Rabi splitting, it is seen by a CP as reduced by a factor 1/√N because of averaging along the cavity axis (G.C. La Rocca, F. Bassani, V.M. Agranovich, JOSA B 15), (1998). As for the in-plane motional narrowing, a simple scaling procedure shows that it would imply that the inhomogeneous linewidth of a CP be reduced by about four orders of magnitude compared to a QW exciton, which is incompatible with the experimental observations. The physical reason of such a shortcoming is that the disorder introduces localized exciton states which can resonantly scatter CPs, mixing them with states having a large k vector as well as with dark exciton states.

  1. Hollow multilayer photonic bandgap fibers for NIR applications

    Science.gov (United States)

    Kuriki, Ken; Shapira, Ofer; Hart, Shandon D.; Benoit, Gilles; Kuriki, Yuka; Viens, Jean F.; Bayindir, Mehmet; Joannopoulos, John D.; Fink, Yoel

    2004-04-01

    Here we report the fabrication of hollow-core cylindrical photonic bandgap fibers with fundamental photonic bandgaps at near-infrared wavelengths, from 0.85 to 2.28 μm. In these fibers the photonic bandgaps are created by an all-solid multilayer composite meso-structure having a photonic crystal lattice period as small as 260 nm, individual layers below 75 nm and as many as 35 periods. These represent, to the best of our knowledge, the smallest period lengths and highest period counts reported to date for hollow PBG fibers. The fibers are drawn from a multilayer preform into extended lengths of fiber. Light is guided in the fibers through a large hollow core that is lined with an interior omnidirectional dielectric mirror. We extend the range of materials that can be used in these fibers to include poly(ether imide) (PEI) in addition to the arsenic triselenide (As2Se3) glass and poly(ether sulfone) (PES) that have been used previously. Further, we characterize the refractive indices of these materials over a broad wavelength range (0.25 - 15 μm) and incorporated the measured optical properties into calculations of the fiber photonic band structure and a preliminary loss analysis.

  2. Bandgap tunability at single-layer molybdenum disulphide grain boundaries

    KAUST Repository

    Huang, Yu Li

    2015-02-17

    Two-dimensional transition metal dichalcogenides have emerged as a new class of semiconductor materials with novel electronic and optical properties of interest to future nanoelectronics technology. Single-layer molybdenum disulphide, which represents a prototype two-dimensional transition metal dichalcogenide, has an electronic bandgap that increases with decreasing layer thickness. Using high-resolution scanning tunnelling microscopy and spectroscopy, we measure the apparent quasiparticle energy gap to be 2.40±0.05 eV for single-layer, 2.10±0.05 eV for bilayer and 1.75±0.05 eV for trilayer molybdenum disulphide, which were directly grown on a graphite substrate by chemical vapour deposition method. More interestingly, we report an unexpected bandgap tunability (as large as 0.85±0.05 eV) with distance from the grain boundary in single-layer molybdenum disulphide, which also depends on the grain misorientation angle. This work opens up new possibilities for flexible electronic and optoelectronic devices with tunable bandgaps that utilize both the control of two-dimensional layer thickness and the grain boundary engineering.

  3. Structure and optical bandgap relationship of π-conjugated systems.

    Science.gov (United States)

    Botelho, André Leitão; Shin, Yongwoo; Liu, Jiakai; Lin, Xi

    2014-01-01

    In bulk heterojunction photovoltaic systems both the open-circuit voltage as well as the short-circuit current, and hence the power conversion efficiency, are dependent on the optical bandgap of the electron-donor material. While first-principles methods are computationally intensive, simpler model Hamiltonian approaches typically suffer from one or more flaws: inability to optimize the geometries for their own input; absence of general, transferable parameters; and poor performance for non-planar systems. We introduce a set of new and revised parameters for the adapted Su-Schrieffer-Heeger (aSSH) Hamiltonian, which is capable of optimizing geometries, along with rules for applying them to any [Formula: see text]-conjugated system containing C, N, O, or S, including non-planar systems. The predicted optical bandgaps show excellent agreement to UV-vis spectroscopy data points from literature, with a coefficient of determination [Formula: see text], a mean error of -0.05 eV, and a mean absolute deviation of 0.16 eV. We use the model to gain insights from PEDOT, fused thiophene polymers, poly-isothianaphthene, copolymers, and pentacene as sources of design rules in the search for low bandgap materials. Using the model as an in-silico design tool, a copolymer of benzodithiophenes along with a small-molecule derivative of pentacene are proposed as optimal donor materials for organic photovoltaics.

  4. Structure and optical bandgap relationship of π-conjugated systems.

    Directory of Open Access Journals (Sweden)

    André Leitão Botelho

    Full Text Available In bulk heterojunction photovoltaic systems both the open-circuit voltage as well as the short-circuit current, and hence the power conversion efficiency, are dependent on the optical bandgap of the electron-donor material. While first-principles methods are computationally intensive, simpler model Hamiltonian approaches typically suffer from one or more flaws: inability to optimize the geometries for their own input; absence of general, transferable parameters; and poor performance for non-planar systems. We introduce a set of new and revised parameters for the adapted Su-Schrieffer-Heeger (aSSH Hamiltonian, which is capable of optimizing geometries, along with rules for applying them to any [Formula: see text]-conjugated system containing C, N, O, or S, including non-planar systems. The predicted optical bandgaps show excellent agreement to UV-vis spectroscopy data points from literature, with a coefficient of determination [Formula: see text], a mean error of -0.05 eV, and a mean absolute deviation of 0.16 eV. We use the model to gain insights from PEDOT, fused thiophene polymers, poly-isothianaphthene, copolymers, and pentacene as sources of design rules in the search for low bandgap materials. Using the model as an in-silico design tool, a copolymer of benzodithiophenes along with a small-molecule derivative of pentacene are proposed as optimal donor materials for organic photovoltaics.

  5. High PSRR bandgap reference used in boost circuit

    Science.gov (United States)

    Li, Yi; Duan, Baoxing; Wang, Yong; Yang, Yintang

    2017-03-01

    Based on pre-regulated voltage structure, a voltage bandgap reference with high power supply rejection ratio (PSRR) is presented in this paper. A pre-regulated voltage structure is used in the circuit to achieve isolating the supply voltage of the bandgap core circuit from VDD to reach a high PSRR. The circuit was designed and simulated in 0.35um BCD technology. The results show the output voltage variation versus temperature (-50°C -100°C) is 8.8 ppm/°C, bandgap reference voltage is 1.236V, current consumption is 30.3 µA. Noise is 53.54 µV/Hz-1/2 at 1Hz. PSRR is -91dB at low frequency, -90.3dB at 1 kHz and -30.3dB at 1MHz. thus, the circuit maintains a good performance in PSRR through a broad frequency.

  6. A generic concept to overcome bandgap limitations for designing highly efficient multi-junction photovoltaic cells.

    Science.gov (United States)

    Guo, Fei; Li, Ning; Fecher, Frank W; Gasparini, Nicola; Ramirez Quiroz, Cesar Omar; Bronnbauer, Carina; Hou, Yi; Radmilović, Vuk V; Radmilović, Velimir R; Spiecker, Erdmann; Forberich, Karen; Brabec, Christoph J

    2015-07-16

    The multi-junction concept is the most relevant approach to overcome the Shockley-Queisser limit for single-junction photovoltaic cells. The record efficiencies of several types of solar technologies are held by series-connected tandem configurations. However, the stringent current-matching criterion presents primarily a material challenge and permanently requires developing and processing novel semiconductors with desired bandgaps and thicknesses. Here we report a generic concept to alleviate this limitation. By integrating series- and parallel-interconnections into a triple-junction configuration, we find significantly relaxed material selection and current-matching constraints. To illustrate the versatile applicability of the proposed triple-junction concept, organic and organic-inorganic hybrid triple-junction solar cells are constructed by printing methods. High fill factors up to 68% without resistive losses are achieved for both organic and hybrid triple-junction devices. Series/parallel triple-junction cells with organic, as well as perovskite-based subcells may become a key technology to further advance the efficiency roadmap of the existing photovoltaic technologies.

  7. Overcoming the Cut-Off Charge Transfer Bandgaps at the PbS Quantum Dot Interface

    KAUST Repository

    El-Ballouli, Ala'a O.

    2015-11-17

    Light harvesting from large size of semiconductor PbS quantum dots (QDs) with a bandgap of less than 1 eV is one of the greatest challenges precluding the development of PbS QD-based solar cells because the interfacial charge transfer (CT) from such QDs to the most commonly used electron acceptor materials is very inefficient, if it occurs at all. Thus, an alternative electron-accepting unit with a new driving force for CT is urgently needed to harvest the light from large-sized PbS QDs. Here, a cationic porphyrin is utilized as a new electron acceptor unit with unique features that bring the donor–acceptor components into close molecular proximity, allowing ultrafast and efficient electron transfer for QDs of all sizes, as inferred from the drastic photoluminescence quenching and the ultrafast formation of the porphyrin anionic species. The time-resolved results clearly demonstrate the possibility of modulating the electron transfer process between PbS QDs and porphyrin moieties not only by the size quantization effect but also by the interfacial electrostatic interaction between the positively charged porphyrin and the negatively charged QDs. This approach provides a new pathway for engineering QD-based solar cells that make the best use of the diverse photons making up the Sun\\'s broad irradiance spectrum.

  8. A generic concept to overcome bandgap limitations for designing highly efficient multi-junction photovoltaic cells

    Science.gov (United States)

    Guo, Fei; Li, Ning; Fecher, Frank W.; Gasparini, Nicola; Quiroz, Cesar Omar Ramirez; Bronnbauer, Carina; Hou, Yi; Radmilović, Vuk V.; Radmilović, Velimir R.; Spiecker, Erdmann; Forberich, Karen; Brabec, Christoph J.

    2015-01-01

    The multi-junction concept is the most relevant approach to overcome the Shockley–Queisser limit for single-junction photovoltaic cells. The record efficiencies of several types of solar technologies are held by series-connected tandem configurations. However, the stringent current-matching criterion presents primarily a material challenge and permanently requires developing and processing novel semiconductors with desired bandgaps and thicknesses. Here we report a generic concept to alleviate this limitation. By integrating series- and parallel-interconnections into a triple-junction configuration, we find significantly relaxed material selection and current-matching constraints. To illustrate the versatile applicability of the proposed triple-junction concept, organic and organic-inorganic hybrid triple-junction solar cells are constructed by printing methods. High fill factors up to 68% without resistive losses are achieved for both organic and hybrid triple-junction devices. Series/parallel triple-junction cells with organic, as well as perovskite-based subcells may become a key technology to further advance the efficiency roadmap of the existing photovoltaic technologies. PMID:26177808

  9. Photonic band-gap and defect modes of a one-dimensional photonic crystal under localized compression

    Science.gov (United States)

    Sánchez, A.; Porta, A. V.; Orozco, S.

    2017-05-01

    The rupture of periodicity caused by one defect (defect layer) in a one-dimensional photonic crystal (1DPhC) results in a narrow transmission spectral line in the photonic band-gap, and the field distribution shows a strong confinement in the proximity of the defect layer. In this work, we present a theoretical model to calculate the frequency of defect modes caused by defect layers induced by localized mechanical stress. Two periodical arrangements were studied: one with layers of poly(methyl-methacrylate) (PMMA) and polystyrene (PS), PMMA-PS; the other with layers of PMMA and fused silica (SiO2), PMMA-SiO2. The defect layers were induced by localized compression (tension). The frequencies of the defect modes were calculated using elasto-optical theory and plane wave expansion and perturbation methods. Numerical results show that the frequency of the defect mode increases (decreases) when the compression (tension) increases. Based on the theoretical model developed, we show that compression of n layers of a 1DPhC induces n defect modes whose frequencies depend on the compression magnitude in the case of normal incidence of electromagnetic waves, in accordance with the results reported for other types of defect layers. The methodology shows the feasibility of the plane wave expansion and perturbation methods to study the frequency of the defect modes. Both periodical arrangements are suitable for designing mechanically tunable (1DPhC)-based narrow pass band filters and narrow reflectors in the (60, 65) THz range.

  10. Advances in thin-film solar cells

    CERN Document Server

    Dharmadasa, I M

    2012-01-01

    This book concentrates on the latest developments in our understanding of solid-state device physics. The material presented is mainly experimental and based on CdTe thin-film solar cells. It extends these new findings to CIGS thin-film solar cells and presents a new device design based on graded bandgap multilayer solar cells. This design has been experimentally tested using the well-researched GaAs/AlGaAs system and initial devices have shown impressive device parameters. These devices are capable of absorbing all radiation (UV, visible, and infra-red) within the solar spectrum and combines

  11. Luminescence in Conjugated Molecular Materials under Sub-bandgap Excitation

    Energy Technology Data Exchange (ETDEWEB)

    So, Franky [University of Florida

    2014-05-08

    Light emission in semiconductors occurs when they are under optical and electrical excitation with energy larger than the bandgap energy. In some low-dimensional semiconductor heterostructure systems, this thermodynamic limit can be violated due to radiative Auger recombination (AR), a process in which the sub-bandgap energy released from a recombined electron-hole pair is transferred to a third particle leading to radiative band-to-band recombination.1 Thus far, photoluminescence up-conversion phenomenon has been observed in some low dimensional semiconductor systems, and the effect is very weak and it can only be observed at low temperatures. Recently, we discovered that efficient electroluminescence in poly[2-methoxy-5-(2’-ethylhexyloxy)-1, phenylenevinylene] (MEH-PPV) polymer light-emitting devices (PLEDs) at drive voltages below its bandgap voltage could be observed when a ZnO nanoparticles (NPs) electron injection layer was inserted between the polymer and the aluminum electrode. Specifically, emitted photons with energy of 2.13 eV can be detected at operating voltages as low as 1.2 V at room temperature. Based on these data, we propose that the sub-bandgap turn-on in the MEH-PPV device is due to an Auger-assisted energy up-conversion process. The significance of this discovery is three-fold. First, radiative recombination occurs at operating voltages below the thermodynamic bandgap voltage. This process can significantly reduce the device operating voltage. For example, the current density of the device with the ZnO NC layer is almost two orders of magnitude higher than that of the device without the NC layer. Second, a reactive metal is no longer needed for the cathode. Third, this electroluminescence up-conversion process can be applied to inorganic semiconductors systems as well and their operation voltages of inorganic LEDs can be reduced to about half of the bandgap energy. Based on our initial data, we propose that the sub-bandgap turn-on in MEH

  12. Broad Diphotons from Narrow States

    CERN Document Server

    An, Haipeng; Zhang, Yue

    2015-01-01

    ATLAS and CMS have each reported a modest diphoton excess consistent with the decay of a broad resonance at ~ 750 GeV. We show how this signal can arise in a weakly coupled theory comprised solely of narrow width particles. In particular, if the decaying particle is produced off-shell, then the associated diphoton resonance will have a broad, adjustable width. We present simplified models which explain the diphoton excess through the three-body decay of a scalar or fermion. Our minimal ultraviolet completion is a weakly coupled and renormalizable theory of a singlet scalar plus a heavy vector-like quark and lepton. The smoking gun of this mechanism is an asymmetric diphoton peak recoiling against missing transverse energy, jets, or leptons.

  13. 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.

  14. Local resonance and Bragg bandgaps in sandwich beams containing periodically inserted resonators

    CERN Document Server

    Sharma, Bhisham

    2015-01-01

    We study the low frequency wave propagation behavior of sandwich beams containing periodically embedded internal resonators. A closed form expression for the propagation constant is obtained using a phased array approach and verified using finite element simulations. We show that local resonance and Bragg bandgaps coexist in such a system and that the width of both bandgaps is a function of resonator parameters as well as their periodicity. The interaction between the two bandgaps is studied by varying the local resonance frequency. We find that a single combined bandgap does not exist for this system and that the Bragg bandgaps transition into sub-wavelength bandgaps when the local resonance frequency is above their associated classical Bragg frequency.

  15. Energy Bandgap and Edge States in an Epitaxially Grown Graphene/h-BN Heterostructure.

    Science.gov (United States)

    Hwang, Beomyong; Hwang, Jeongwoon; Yoon, Jong Keon; Lim, Sungjun; Kim, Sungmin; Lee, Minjun; Kwon, Jeong Hoon; Baek, Hongwoo; Sung, Dongchul; Kim, Gunn; Hong, Suklyun; Ihm, Jisoon; Stroscio, Joseph A; Kuk, Young

    2016-08-09

    Securing a semiconducting bandgap is essential for applying graphene layers in switching devices. Theoretical studies have suggested a created bulk bandgap in a graphene layer by introducing an asymmetry between the A and B sub-lattice sites. A recent transport measurement demonstrated the presence of a bandgap in a graphene layer where the asymmetry was introduced by placing a graphene layer on a hexagonal boron nitride (h-BN) substrate. Similar bandgap has been observed in graphene layers on metal substrates by local probe measurements; however, this phenomenon has not been observed in graphene layers on a near-insulating substrate. Here, we present bulk bandgap-like features in a graphene layer epitaxially grown on an h-BN substrate using scanning tunneling spectroscopy. We observed edge states at zigzag edges, edge resonances at armchair edges, and bandgap-like features in the bulk.

  16. Energy Bandgap and Edge States in an Epitaxially Grown Graphene/h-BN Heterostructure

    Science.gov (United States)

    Hwang, Beomyong; Hwang, Jeongwoon; Yoon, Jong Keon; Lim, Sungjun; Kim, Sungmin; Lee, Minjun; Kwon, Jeong Hoon; Baek, Hongwoo; Sung, Dongchul; Kim, Gunn; Hong, Suklyun; Ihm, Jisoon; Stroscio, Joseph A.; Kuk, Young

    2016-08-01

    Securing a semiconducting bandgap is essential for applying graphene layers in switching devices. Theoretical studies have suggested a created bulk bandgap in a graphene layer by introducing an asymmetry between the A and B sub-lattice sites. A recent transport measurement demonstrated the presence of a bandgap in a graphene layer where the asymmetry was introduced by placing a graphene layer on a hexagonal boron nitride (h-BN) substrate. Similar bandgap has been observed in graphene layers on metal substrates by local probe measurements; however, this phenomenon has not been observed in graphene layers on a near-insulating substrate. Here, we present bulk bandgap-like features in a graphene layer epitaxially grown on an h-BN substrate using scanning tunneling spectroscopy. We observed edge states at zigzag edges, edge resonances at armchair edges, and bandgap-like features in the bulk.

  17. Cryogenic Detectors (Narrow Field Instruments)

    Science.gov (United States)

    Hoevers, H.; Verhoeve, P.

    Two cryogenic imaging spectrometer arrays are currently considered as focal plane instruments for XEUS. The narrow field imager 1 (NFI 1) will cover the energy range from 0.05 to 3 keV with an energy resolution of 2 eV, or better, at 500 eV. A second narrow field imager (NFI 2) covers the energy range from 1 to 15 keV with an energy resolution of 2 eV (at 1 keV) and 5 eV (at 7 keV), creating some overlap with part of the NFI 1 energy window. Both narrow field imagers have a 0.5 arcmin field of view. Their imaging capabilities are matched to the XEUS optics of 2 to 5 arcsec leading to 1 arcsec pixels. The detector arrays will be cooled by a closed cycle system comprising a mechanical cooler with a base temperature of 2.5 K and either a low temperature 3He sorption pump providing the very low temperature stage and/or an Adiabatic Demagnetization Refrigerator (ADR). The ADR cooler is explicitly needed to cool the NFI 2 array. The narrow field imager 1} Currently a 48 times 48 element array of superconducting tunnel junctions (STJ) is envisaged. Its operating temperature is in the range between 30 and 350 mK. Small, single Ta STJs (20-50 mum on a side) have shown 3.5 eV (FWHM) resolution at E = 525 eV and small arrays have been successfully demonstrated (6 times 6 pixels), or are currently tested (10 times 12 pixels). Alternatively, a prototype Distributed Read-Out Imaging Device (DROID), consisting of a linear superconducting Ta absorber of 20 times 100 mum2, including a 20 times 20 mum STJ for readout at either end, has shown a measured energy resolution of 2.4 eV (FWHM) at E = 500 eV. Simulations involving the diffusion properties as well as loss and tunnel rates have shown that the performance can be further improved by slight modifications in the geometry, and that the size of the DROIDS can be increased to 0.5-1.0 mm without loss in energy resolution. The relatively large areas and good energy resolution compared to single STJs make DROIDS good candidates for the

  18. Photoelectrochemistry, Electronic Structure, and Bandgap Sizes of Semiconducting Cu(I)-Niobates and Cu(I)-Tantalates

    Energy Technology Data Exchange (ETDEWEB)

    Maggard, Paul A.

    2013-11-14

    Semiconducting metal-oxides have remained of intense research interest owing to their potential for achieving efficient solar-driven photocatalytic reactions in aqueous solutions that occur as a result of their bandgap excitation. The photocatalytic reduction of water or carbon dioxide to generate hydrogen or hydrocarbon fuels, respectively, can be driven on p-type (photocathodic) electrodes with suitable band energies. However, metal-oxide semiconductors are typically difficult to dope as p-type with a high mobility of carriers. The supported research led to the discovery of new p-type Cu(I)-niobate and Cu(I)-tantalate film electrodes that can be prepared on FTO glass. New high-purity flux syntheses and the full structural determination of several Cu(I)-containing niobates and tantalates have been completed, as well as new investigations of their optical and photoelectrochemical properties and electronic structures via density-functional theory calculations. For example, CuNbO3, Cu5Ta11O30 and CuNb3O8 were prepared in high purity and their structures were characterized by both single-crystal and powder X-ray diffraction techniques. These two classes of Cu(I)-containing compounds exhibit optical bandgap sizes ranging from ~1.3 eV to ~2.6 eV. Photoelectrochemical measurements of these compounds show strong photon-driven cathodic currents that confirm the p-type semiconductor behavior of CuNbO3, CuNb3O8, and Cu5Ta11O30. Incident-photon-to-current efficiencies are measured that approach greater than ~1%. Electronic-structure calculations based on density functional theory reveal the visible-light absorption stems from a nearly-direct bandgap transition involving a copper-to-niobium or tantalum (d10 to d0) charge-transfer excitations.

  19. Maximizing bandgaps in two-dimensional photonic crystals a variational algorithm

    CERN Document Server

    Paul, P; Paul, Prabasaj; Ndi, Francis C.

    2002-01-01

    We present an algorithm for the maximization of photonic bandgaps in two-dimensional crystals. Once the translational symmetries of the underlying structure have been imposed, our algorithm finds a global maximal (and complete, if one exists) bandgap. Additionally, we prove two remarkable results related to maximal bandgaps: the so-called `maximum contrast' rule, and about the location in the Brillouin zone of band edges.

  20. Application of pressure to shift the bandgap in polystyrene-based photonic crystals

    Science.gov (United States)

    Johnson, Nigel P.; Khokhar, Ali Z.; McLachlan, Martyn A.; McComb, David W.; De La Rue, Richard M.

    2004-09-01

    We describe a simple technique for the selective area modification of the bandgap in planar 3-D photonic crystals (PhC). The PhCs are grown by controlled drying of monosized polystyrene spheres. Uniaxial pressure of 41 MPa can produce a shift in the bandgap of ~90 nm from 230 nm spheres. An unexpected broadening of the bandgap is attributed to the change in topology associated with large necks formed between spheres at pressures greater than 10 MPa.

  1. Exploring Direct to Indirect Bandgap Transition in Silicon Nanowires: Size Effect

    Science.gov (United States)

    Shi, Lihong; Zhang, Gang

    2016-10-01

    We have investigated the electronic band structure of [110] silicon nanowires (SiNWs) using first-principles calculations. We find that, in the ultrathin diameter regime, SiNWs have a direct bandgap, but the energy difference between the indirect and direct fundamental bandgaps decreases as the nanowire diameter increases. This indicates that larger [110] SiNWs could have an indirect bandgap. Fundamentally, a series of quantitative direct-indirect bandgap transitional diameters are obtained for different cross-sectional geometries, with the largest values for SiNWs with triangular cross section.

  2. Urbach's rule derived from thermal fluctuations in the band-gap energy

    DEFF Research Database (Denmark)

    Skettrup, Torben

    1978-01-01

    The exponential absorption edge (known as Urbach's rule) observed in most materials is interpreted in terms of thermal fluctuations in the band-gap energy. The main contribution to the temperature shift of the band-gap energy is due to the temperature-dependent self-energies of the electrons...... and holes interacting with the phonons. Since the phonon number is fluctuating in thermal equilibrium, the band-gap energy is also fluctuating resulting in an exponential absorption tail below the average band-gap energy. These simple considerations are applied to derive Urbach's rule at high temperatures...

  3. New UV detectors for solar observations

    Science.gov (United States)

    Hochedez, Jean-Francois E.; Schuehle, Udo H.; Pau, Jose L.; Alvarez, Jose; Hainaut, Olivier; Appourchaux, Thierry P.; Auret, F. D.; Belsky, Andrei; Bergonzo, Philippe; Castex, M. C.; Deneuville, A.; Dhez, Pierre; Fleck, Bernhard; Haenen, Ken; Idir, Mourad; Kleider, Jean Paul; Lefeuvre, Elie; Lemaire, Philippe; Monroy, E.; Muret, P.; Munoz, Elias; Nesladek, Milos; Omnes, Franck; Pace, Emanuele; Peacock, Anthony J.; Van Hoof, Chris A.

    2003-02-01

    BOLD (Blind to the Optical Light Detectors) is an international initiative dedicated to the development of novel imaging detectors for UV solar observations. It relies on the properties of wide bandgap materials (in particular diamond and Al-Ga-nitrides). The investigation is proposed in view of the Solar Orbiter (S.O.) UV instruments, for which the expected benefits of the new sensors -primarily visible blindness and radiation hardness- will be highly valuable. Despite various advances in the technology of imaging detectors over the last decades, the present UV imagers based on silicon CCDs or microchannel plates exhibit limitations inherent to their actual material and technology. Yet, the utmost spatial resolution, fast temporal cadence, sensitivity, and photometric accuracy will be decisive for the forthcoming solar space missions. The advent of imagers based on wide-bandgap materials will permit new observations and, by simplifying their design, cheaper instruments. As for the Solar Orbiter, the aspiration for wide-bandgap material (WBGM) based UV detectors is still more sensible because the spacecraft will approach the Sun where the heat and the radiation fluxes are high. We describe the motivations, and present the program to achieve revolutionary flight cameras within the Solar Orbiter schedule as well as relevant UV measurements.

  4. High bandgap III-V alloys for high efficiency optoelectronics

    Science.gov (United States)

    Alberi, Kirstin; Mascarenhas, Angelo; Wanlass, Mark

    2017-01-10

    High bandgap alloys for high efficiency optoelectronics are disclosed. An exemplary optoelectronic device may include a substrate, at least one Al.sub.1-xIn.sub.xP layer, and a step-grade buffer between the substrate and at least one Al.sub.1-xIn.sub.xP layer. The buffer may begin with a layer that is substantially lattice matched to GaAs, and may then incrementally increase the lattice constant in each sequential layer until a predetermined lattice constant of Al.sub.1-xIn.sub.xP is reached.

  5. Soliton formation in hollow-core photonic bandgap fibers

    DEFF Research Database (Denmark)

    Lægsgaard, Jesper

    2009-01-01

    of an approximate scaling relation is tested. It is concluded that compression of input pulses of several ps duration and sub-MW peak power can lead to a formation of solitons with ∼100 fs duration and multi-megawatt peak powers. The dispersion slope of realistic hollow-core fibers appears to be the main obstacle......The formation of solitons upon compression of linearly chirped pulses in hollow-core photonic bandgap fibers is investigated numerically. The dependence of soliton duration on the chirp and power of the input pulse and on the dispersion slope of the fiber is investigated, and the validity...

  6. Accurate modelling of fabricated hollow-core photonic bandgap fibers.

    Science.gov (United States)

    Fokoua, Eric Numkam; Sandoghchi, Seyed Reza; Chen, Yong; Jasion, Gregory T; Wheeler, Natalie V; Baddela, Naveen K; Hayes, John R; Petrovich, Marco N; Richardson, David J; Poletti, Francesco

    2015-09-07

    We report a novel approach to reconstruct the cross-sectional profile of fabricated hollow-core photonic bandgap fibers from scanning electron microscope images. Finite element simulations on the reconstructed geometries achieve a remarkable match with the measured transmission window, surface mode position and attenuation. The agreement between estimated scattering loss from surface roughness and measured loss values indicates that structural distortions, in particular the uneven distribution of glass across the thin silica struts on the core boundary, have a strong impact on the loss. This provides insight into the differences between idealized models and fabricated fibers, which could be key to further fiber loss reduction.

  7. Liquid-impermeable inverse opals with invariant photonic bandgap.

    Science.gov (United States)

    Kang, Hyelim; Lee, Joon-Seok; Chang, Won Seok; Kim, Shin-Hyun

    2015-02-18

    Omniphobic inverse opals are created by structurally and chemically modifying the surface of inverse opals through reactive ion etching. During the etching, void arrays of the inverse opal surface evolves to a triangular post array with re-entrant geometry. The elaborate structure can efficiently pin the air-liquid interface and retain air cavities against water and oil, thereby providing liquid-impermeable inverse opals with invariant photonic bandgap. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. High bandgap III-V alloys for high efficiency optoelectronics

    Energy Technology Data Exchange (ETDEWEB)

    Alberi, Kirstin; Mascarenhas, Angelo; Wanlass, Mark

    2017-01-10

    High bandgap alloys for high efficiency optoelectronics are disclosed. An exemplary optoelectronic device may include a substrate, at least one Al.sub.1-xIn.sub.xP layer, and a step-grade buffer between the substrate and at least one Al.sub.1-xIn.sub.xP layer. The buffer may begin with a layer that is substantially lattice matched to GaAs, and may then incrementally increase the lattice constant in each sequential layer until a predetermined lattice constant of Al.sub.1-xIn.sub.xP is reached.

  9. Waveguidance by the photonic bandgap effect in optical fibres

    DEFF Research Database (Denmark)

    Broeng, Jes; Søndergaard, Thomas; Barkou, Stig Eigil;

    1999-01-01

    Photonic crystals form a new class of intriguing building blocks to be utilized in future optoelectronics and electromagnetics. One of the most exciting possiblilties offered by phtonic crystals is the realization of new types of electromagnetic waveguides. In the optical domain, the most mature...... technology for such photonic bandgap (PBG) waveguides is in optical fibre configurations. These new fibres can be classified in a fundamentally different way to all optical waveguides and possess radically different guiding properties due to PBG guidance, as opposed to guidance by total internal refelction...

  10. Formation of the Terrestrial Planets from a Narrow Annulus

    CERN Document Server

    Hansen, Brad

    2009-01-01

    We show that the assembly of the Solar System terrestrial planets can be successfully modelled with all of the mass initially confined to a narrow annulus between 0.7 and 1.0 AU. With this configuration, analogues of Mercury and Mars often form from the collisional evolution of material diffusing out of the annulus under the scattering of the forming Earth and Venus analogues. The final systems also possess eccentricities and inclinations that match the observations, without recourse to dynamical friction from remnant small body populations. Finally, the characteristic assembly timescale for Earth analogues is rapid in this model, and consistent with cosmochemical models based on the $^{182}$Hf--$^{182}$W isotopes. The agreement between this model and the observations suggests that terrestrial planet systems may also be formed in `planet traps', as has been proposed recently for the cores of giant planets in our solar system and others.

  11. Anger perceptually and conceptually narrows cognitive scope.

    Science.gov (United States)

    Gable, Philip A; Poole, Bryan D; Harmon-Jones, Eddie

    2015-07-01

    For the last 50 years, research investigating the effect of emotions on scope of cognitive processing was based on models proposing that affective valence determined cognitive scope. More recently, our motivational intensity model suggests that this past work had confounded valence with motivational intensity. Research derived from this model supports the idea that motivational intensity, rather than affective valence, explains much of the variance emotions have on cognitive scope. However, the motivational intensity model is limited in that the empirical work has examined only positive affects high in approach and negative affects high in avoidance motivation. Thus, perhaps only approach-positive and avoidance-negative states narrow cognitive scope. The present research was designed to clarify these conceptual issues by examining the effect of anger, a negatively valenced approach-motivated state, on cognitive scope. Results revealed that anger narrowed attentional scope relative to a neutral state and that attentional narrowing to anger was similar to the attentional narrowing caused by high approach-motivated positive affects (Study 1). This narrowing of attention was related to trait approach motivation (Studies 2 and Study 3). Anger also narrowed conceptual cognitive categorization (Study 4). Narrowing of categorization related to participants' approach motivation toward anger stimuli. Together, these results suggest that anger, an approach-motivated negative affect, narrows perceptual and conceptual cognitive scope. More broadly, these results support the conceptual model that motivational intensity per se, rather than approach-positive and avoidance-negative states, causes a narrowing of cognitive scope.

  12. Electronic structure characterization and bandgap engineeringofsolar hydrogen materials

    Energy Technology Data Exchange (ETDEWEB)

    Guo, Jinghua

    2007-11-01

    Bandgap, band edge positions as well as the overall band structure of semiconductors are of crucial importance in photoelectrochemical and photocatalytic applications. The energy position of the band edge level can be controlled by the electronegativity of the dopants, the pH of the solution (flatband potential variation of 60 mV per pH unit), as well as by quantum confinement effects. Accordingly, band edges and bandgap can be tailored to achieve specific electronic, optical or photocatalytic properties. Synchrotron radiation with photon energy at or below 1 keV is giving new insight into such areas as condensed matter physics and extreme ultraviolet optics technology. In the soft x-ray region, the question tends to be, what are the electrons doing as they migrated between the atoms. In this paper, I will present a number of soft x-ray spectroscopic study of nanostructured 3d metal compounds Fe{sub 2}O{sub 3} and ZnO.

  13. Graded bandgap semiconduc-tor thin film photoelectrodes

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    A graded bandgap oxide semiconductor thin film electrode was designed in order to obtain a photoelectrochemically stable photoelectrode, with wide absorption range. The graded bandgap Ti1-xVxO2 film electrode was prepared by heating the stacked layers of V/Ti in varying ratios, which were coated on the substrate by the sol-gel method using the starting solution with various V/Ti ratios. XPS result showed that the composition gradient was achieved for the film. The Ti1-xVxO2 film electrode was found to be photoelectrochemically stable. Its photovoltage was about 360 mV. Obvious visible light photoresponse was observed for the Ti1-xVxO2 film electrode. Compared with the pure TiO2 electrode, the photocurrent onset potential of the Ti1-xVxO2 film electrode was shifted positively, probably because the accumulation of vanadium at the electrode sur-face causes the recombination of the electrons and holes, and the lowest level of the conduction band of Ti1-xVxO2 is lower than that of TiO2. Impedance analysis showed that the donor density of the Ti1-xVxO2 film electrode was higher than that of TiO2 film electrode.

  14. Lyapunov exponents for one-dimensional aperiodic photonic bandgap structures

    Science.gov (United States)

    Kissel, Glen J.

    2011-10-01

    Existing in the "gray area" between perfectly periodic and purely randomized photonic bandgap structures are the socalled aperoidic structures whose layers are chosen according to some deterministic rule. We consider here a onedimensional photonic bandgap structure, a quarter-wave stack, with the layer thickness of one of the bilayers subject to being either thin or thick according to five deterministic sequence rules and binary random selection. To produce these aperiodic structures we examine the following sequences: Fibonacci, Thue-Morse, Period doubling, Rudin-Shapiro, as well as the triadic Cantor sequence. We model these structures numerically with a long chain (approximately 5,000,000) of transfer matrices, and then use the reliable algorithm of Wolf to calculate the (upper) Lyapunov exponent for the long product of matrices. The Lyapunov exponent is the statistically well-behaved variable used to characterize the Anderson localization effect (exponential confinement) when the layers are randomized, so its calculation allows us to more precisely compare the purely randomized structure with its aperiodic counterparts. It is found that the aperiodic photonic systems show much fine structure in their Lyapunov exponents as a function of frequency, and, in a number of cases, the exponents are quite obviously fractal.

  15. Optical bandgap of semiconductor nanostructures: Methods for experimental data analysis

    Science.gov (United States)

    Raciti, R.; Bahariqushchi, R.; Summonte, C.; Aydinli, A.; Terrasi, A.; Mirabella, S.

    2017-06-01

    Determination of the optical bandgap (Eg) in semiconductor nanostructures is a key issue in understanding the extent of quantum confinement effects (QCE) on electronic properties and it usually involves some analytical approximation in experimental data reduction and modeling of the light absorption processes. Here, we compare some of the analytical procedures frequently used to evaluate the optical bandgap from reflectance (R) and transmittance (T) spectra. Ge quantum wells and quantum dots embedded in SiO2 were produced by plasma enhanced chemical vapor deposition, and light absorption was characterized by UV-Vis/NIR spectrophotometry. R&T elaboration to extract the absorption spectra was conducted by two approximated methods (single or double pass approximation, single pass analysis, and double pass analysis, respectively) followed by Eg evaluation through linear fit of Tauc or Cody plots. Direct fitting of R&T spectra through a Tauc-Lorentz oscillator model is used as comparison. Methods and data are discussed also in terms of the light absorption process in the presence of QCE. The reported data show that, despite the approximation, the DPA approach joined with Tauc plot gives reliable results, with clear advantages in terms of computational efforts and understanding of QCE.

  16. Petahertz optical drive with wide-bandgap semiconductor

    Science.gov (United States)

    Mashiko, Hiroki; Oguri, Katsuya; Yamaguchi, Tomohiko; Suda, Akira; Gotoh, Hideki

    2016-08-01

    High-speed photonic and electronic devices at present rely on radiofrequency electric fields to control the physical properties of a semiconductor, which limits their operating speed to terahertz frequencies (1012 Hz ref. ). Using the electric field from intense light pulses, however, could extend the operating frequency into the petahertz regime (1015 Hz ref. ). Here we demonstrate optical driving at a petahertz frequency in the wide-bandgap semiconductor gallium nitride. Few-cycle near-infrared pulses are shown to induce electric interband polarization though a multiphoton process. Dipole oscillations with a periodicity of 860 as are revealed in the gallium nitride electron and hole system by using the quantum interference between the two transitions from the valence and conduction band states, which are probed by an extremely short isolated attosecond pulse with a coherent broadband spectrum. In principle, this shows that the conductivity of the semiconductor can be manipulated on attosecond timescales, which corresponds to instantaneous light-induced switching from insulator to conductor. The resultant dipole frequency reaches 1.16 PHz, showing the potential for future high-speed signal processing technologies based on wide-bandgap semiconductors.

  17. A simple model for approximate bandgap structure calculation of all-solid photonic bandgap fibre based on an array of rings

    Institute of Scientific and Technical Information of China (English)

    Fang Hong; Lou Shu-Qin; Guo Tie-Ying; Yao Lei; Li nong-Lei; Jian ShuiSheng

    2008-01-01

    A simple model for approximate bandgap structure caculation of all-solid photonic bandgap fibre based on an array of rings is proposed.In this model calculated are only the potential modes of a unit cell,which is a high-index ring in the low-index background for this fibre,rather than the whole cladding periodic structure based on Bloch's theorem to find the bandgap.Its accuracy is proved by comparing its results with the results obtained by using the accurate full-vector plane-wave method.High speed in computation is its great advantage over the other exact methods,because it only needs to find the roots of one-dimensional analytical expressions.And the results of this model,mode plots,offer an ideal environment to explore the basic properties of photonic bandgap clearly.

  18. Metallic-like bonding in plasma-born silicon nanocrystals for nanoscale bandgap engineering.

    Science.gov (United States)

    Vach, Holger; Ivanova, Lena V; Timerghazin, Qadir K; Jardali, Fatme; Le, Ha-Linh Thi

    2016-10-27

    Based on ab initio molecular dynamics simulations, we show that small nanoclusters of about 1 nm size spontaneously generated in a low-temperature silane plasma do not possess tetrahedral structures, but are ultrastable. Apparently small differences in the cluster structure result in substantial modifications in their electric, magnetic, and optical properties, without the need for any dopants. Their non-tetrahedral geometries notably lead to electron deficient bonds that introduce efficient electron delocalization that strongly resembles the one of a homogeneous electron gas leading to metallic-like bonding within a semiconductor nanocrystal. As a result, pure hydrogenated silicon clusters that form by self-assembly in a plasma reactor possess optical gaps covering most of the solar spectrum from 1.0 eV to 5.2 eV depending simply on their structure and, in turn, on their degree of electron delocalization. This feature makes them ideal candidates for future bandgap engineering not only for photovoltaics, but also for many nano-electronic devices employing nothing else but silicon and hydrogen atoms.

  19. The Effect of LUMO Level Offset on the Electron Dissociation Rates in Low Bandgap Polymer Heterostructures

    Science.gov (United States)

    Sfeir, Matthew; Rodovsky, Deanna; Azoulay, Jason; Bazan, Guillermo; Peet, Jeffrey

    2012-02-01

    In order to maximize the efficiency of polymer/fullerene bulk heterojunction solar cells, the voltage lost when the electron transfers from the polymer to the fullerene must be minimized. While the magnitude of this loss will significantly impact the maximum attainable efficiency of this technology, there have been relatively few attempts to quantify the dependence of the electron transfer rate and yield on the driving force for electron transfer. In order to isolate the effect of electrochemical potential difference on the exciton dissociation rate, we present results of photophysical measurements of a low bandgap copolymer mixed with a series of fullerene based acceptor materials in a bulk heterojunction geometry. The LUMO level of the acceptor material is varied relative to the polymer's so that the effect of the energy offset on the electron dissociation rate can be determined. Using photoluminescence and transient absorption measurements, we find that the exciton quenching rate varies systematically with increasing energy offset. We examine the mechanism of charge carrier generation by correlating the exciton quenching with charge carrier generation.

  20. Solar Superabsorption of Semiconductor Materials

    CERN Document Server

    Yu, Yiling; Cao, Linyou

    2013-01-01

    We theoretically demonstrate the fundamental limit in volume for given materials (e.g. Si, a-Si, CdTe) to fully absorb the solar radiation above bandgap, which we refer as solar superabsorption limit. We also point out the general principles for experimentally designing light trapping structures to approach the superabsorption. This study builds upon an intuitive model, coupled leaky mode theory (CLMT), for the analysis of light absorption in nanostructures. The CLMT provides a useful variable transformation. Unlike the existing methods that rely on information of physical features (e.g. morphology, dimensionality) to analyze light absorption, the CLMT can evaluate light absorption in given materials with only two variables, the radiative loss and the resonant wavelength, of leaky modes, regardless the physical features of the materials. This transformation allows for surveying the entire variable space to find out the solar superabsorption and provides physical insights to guide the design of solar superabso...

  1. Characterization of Doped Amorphous Silicon Thin Films through the Investigation of Dopant Elements by Glow Discharge Spectrometry: A Correlation of Conductivity and Bandgap Energy Measurements

    Directory of Open Access Journals (Sweden)

    Rosario Pereiro

    2011-03-01

    Full Text Available The determination of optical parameters, such as absorption and extinction coefficients, refractive index and the bandgap energy, is crucial to understand the behavior and final efficiency of thin film solar cells based on hydrogenated amorphous silicon (a-Si:H. The influence of small variations of the gas flow rates used for the preparation of the p-a-SiC:H layer on the bandgap energy, as well as on the dopant elements concentration, thickness and conductivity of the p-layer, is investigated in this work using several complementary techniques. UV-NIR spectrophotometry and ellipsometry were used for the determination of bandgap energies of four p-a-SiC:H thin films, prepared by using different B2H6 and SiH4 fluxes (B2H6 from 12 sccm to 20 sccm and SiH4 from 6 sccm to 10 sccm. Moreover, radiofrequency glow discharge optical emission spectrometry technique was used for depth profiling characterization of p-a-SiC:H thin films and valuable information about dopant elements concentration and distribution throughout the coating was found. Finally, a direct relationship between the conductivity of p-a-SiC:H thin films and the dopant elements concentration, particularly boron and carbon, was observed for the four selected samples.

  2. Power-scalable long-wavelength Yb-doped photonic bandgap fiber sources

    DEFF Research Database (Denmark)

    Olausson, Christina Bjarnal Thulin; Shirakawa, Akira; Maurayama, Hiroki

    2010-01-01

    Ytterbium-doped photonic-bandgap fiber sources operationg at the long-wavelength edge of the ytterbium gain band are being investigated for high power amplification. Artificial shaping of the gain spectrum by the characteristic distributed filtering effect of the photonic bandgap enables...

  3. High Thermal and Electrical Tunability of Negative Dielectric Liquid Crystal Photonic Bandgap Fibers

    DEFF Research Database (Denmark)

    Wei, Lei; Scolari, Lara; Weirich, Johannes;

    2008-01-01

    We infiltrate photonic crystal fibers with negative dielectric liquid crystals. 400nm bandgap shift is obtained in the range 22ºC-80ºC and 119nm shift of the long-wavelength bandgap edge is achieved by applying a voltage of 200V....

  4. True photonic band-gap mode-control in VCSEL structures

    DEFF Research Database (Denmark)

    Romstad, F.; Madsen, M.; Birkedal, Dan;

    2003-01-01

    Photonic band-gap mode confinement in novel nano-structured large area VCSEL structures is confirmed by the amplified spontaneous emission spectrum. Both guide and anti-guide VCSEL structures are experimentally characterised to verify the photonic band-gap effect....

  5. Investigating Bandgap Energies, Materials, and Design of Light-Emitting Diodes

    Science.gov (United States)

    Wagner, Eugene P., II

    2016-01-01

    A student laboratory experiment to investigate the intrinsic and extrinsic bandgaps, dopant materials, and diode design in light-emitting diodes (LEDs) is presented. The LED intrinsic bandgap is determined by passing a small constant current through the diode and recording the junction voltage variation with temperature. A second visible…

  6. Semitransparent organic solar cells with organic wavelength dependent reflectors

    NARCIS (Netherlands)

    Galagan, Y.O.; Debije, M.G.; Blom, P.W.M.

    2011-01-01

    Semitransparent organic solar cells employing solution-processable organic wavelength dependent reflectors of chiral nematic (cholesteric) liquid crystals are demonstrated. The cholesteric liquid crystal (CLC) reflects only in a narrow band of the solar spectrum and remains transparent for the

  7. Quantum Dot Solar Cells

    Science.gov (United States)

    Raffaelle, Ryne P.; Castro, Stephanie L.; Hepp, Aloysius; Bailey, Sheila G.

    2002-01-01

    We have been investigating the synthesis of quantum dots of CdSe, CuInS2, and CuInSe2 for use in an intermediate bandgap solar cell. We have prepared a variety of quantum dots using the typical organometallic synthesis routes pioneered by Bawendi, et. al., in the early 1990's. However, unlike previous work in this area we have also utilized single-source precursor molecules in the synthesis process. We will present XRD, TEM, SEM and EDS characterization of our initial attempts at fabricating these quantum dots. Investigation of the size distributions of these nanoparticles via laser light scattering and scanning electron microscopy will be presented. Theoretical estimates on appropriate quantum dot composition, size, and inter-dot spacing along with potential scenarios for solar cell fabrication will be discussed.

  8. Tunable bandgap in few-layer black phosphorus by electrical field

    Science.gov (United States)

    Li, Dong; Xu, Jin-Rong; Ba, Kun; Xuan, Ningning; Chen, Mingyuan; Sun, Zhengzong; Zhang, Yu-Zhong; Zhang, Zengxing

    2017-09-01

    Dynamically engineering bandgap in semiconductors may enable a flexible design and optimization of electronics and optoelectronics. Layered black phosphorus is a 2D semiconductor with a direct bandgap and promising device characteristics. Theoretical studies indicate that the bandgap in black phosphorus can be tuned by electrical field. Here, through designing a double-gated field-effect transistor device configuration, we experimentally demonstrate that the bandgap in few-layer black phosphorus can be dynamically continually tuned by perpendicular electrical field. With an electrical displacement field of 1 V nm-1, the detailed study indicates that the bandgap can reduce around 100 meV. The finding here should be helpful on the flexible design and optimization of black phosphorus electronics and optoelectronics, and may open up some other new possible applications.

  9. Bandgap Engineering of Double Perovskites for One- and Two-photon Water Splitting

    DEFF Research Database (Denmark)

    Castelli, Ivano Eligio; Thygesen, Kristian Sommer; Jacobsen, Karsten Wedel

    2013-01-01

    Computational screening is becoming increasingly useful in the search for new materials. We are interested in the design of new semiconductors to be used for light harvesting in a photoelectrochemical cell. In the present paper, we study the double perovskite structures obtained by combining 46...... stable cubic perovskites which was found to have a finite bandgap in a previous screening-study. The four-metal double perovskite space is too large to be investigated completely. For this reason we propose a method for combining different metals to obtain a desired bandgap. We derive some bandgap design...... rules on how to combine two cubic perovskites to generate a new combination with a larger or smaller bandgap compared with the constituent structures. Those rules are based on the type of orbitals involved in the conduction bands and on the size of the two cubic bandgaps. We also see that a change...

  10. On topology optimization of acoustic metamaterial lattices for locally resonant bandgaps of flexural waves

    CERN Document Server

    Hedayatrasa, Saeid; Uddin, Mohammad

    2016-01-01

    Optimized topology of bi-material acoustic metamaterial lattice plates is studied for maximized locally resonant bandgap of flexural guided waves. Optimized layout of the two relatively stiff and compliant material phases in the design domain is explored, free from any restrictions on the topology and shape of the relevant domains. Multiobjective optimization is performed through which maximized effective stiffness or minimized overall mass of the bandgap topology is additionally ensured. Extreme and selected intermediate optimized topologies of Pareto fronts are presented and their bandgap efficiencies and effective stiffness are compared. The bi-material constitution of selected topologies are further altered and modal band structure of resultant multilateral and porous designs are evaluated. Novel, core-shell like, locally resonant bandgaps are introduced. It is shown that how the bandgap efficiency and structural mass and/or stiffness can be optimized through optimized microstructural design of the matrix...

  11. Influences of the non-covalent interaction strength on reaching high solid-state order and device performance of a low bandgap polymer with axisymmetrical structural units.

    Science.gov (United States)

    Jheng, Jyun-Fong; Lai, Yu-Ying; Wu, Jhong-Sian; Chao, Yi-Hsiang; Wang, Chien-Lung; Hsu, Chain-Shu

    2013-05-07

    A high organic field-effect transistor mobility (0.29 cm(2) V(-1) s(-1) ) and bulk-heterojunction polymer solar cell performance (PCE of 6.82%) have been achieved in a low bandgap alternating copolymer consisting of axisymmetrical structural units, 5,6-difluorobenzo-2,1,3-thiadiazole. Introducing the fluorine substituents enhanced intermolecular interaction and improved the solid-state order, which consequently resulted in the highest device performances among the 2,1,3-thiadiazole-quarterthiophene based alternating copolymers.

  12. Effect of band gap narrowing on GaAs tunnel diode I-V characteristics

    Science.gov (United States)

    Lebib, A.; Hannanchi, R.; Beji, L.; EL Jani, B.

    2016-12-01

    We report on experimental and theoretical study of current-voltage characteristics of C/Si-doped GaAs tunnel diode. For the investigation of the experimental data, we take into account the band-gap narrowing (BGN) effect due to heavily-doped sides of the tunnel diode. The BGN of the n- and p-sides of tunnel diode was measured by photoluminescence spectroscopy. The comparison between theoretical results and experimental data reveals that BGN effect enhances tunneling currents and hence should be considered to identify more accurately the different transport mechanisms in the junction. For C/Si-doped GaAs tunnel diode, we found that direct tunneling is the dominant transport mechanism at low voltages. At higher voltages, this mechanism is replaced by the rate-controlling tunneling via gap states in the forbidden gap.

  13. Effect of band gap narrowing on GaAs tunnel diode I-V characteristics

    Energy Technology Data Exchange (ETDEWEB)

    Lebib, A.; Hannanchi, R. [Laboratoire d' énergie et de matériaux, LabEM-LR11ES34-Université de sousse (Tunisia); Beji, L., E-mail: lotbej_fr@yahoo.fr [Laboratoire d' énergie et de matériaux, LabEM-LR11ES34-Université de sousse (Tunisia); EL Jani, B. [Unité de Recherche sur les Hétéro-Epitaxies et Applications, Faculté des Sciences, Université de Monastir, 5019 Monastir (Tunisia)

    2016-12-01

    We report on experimental and theoretical study of current-voltage characteristics of C/Si-doped GaAs tunnel diode. For the investigation of the experimental data, we take into account the band-gap narrowing (BGN) effect due to heavily-doped sides of the tunnel diode. The BGN of the n- and p-sides of tunnel diode was measured by photoluminescence spectroscopy. The comparison between theoretical results and experimental data reveals that BGN effect enhances tunneling currents and hence should be considered to identify more accurately the different transport mechanisms in the junction. For C/Si-doped GaAs tunnel diode, we found that direct tunneling is the dominant transport mechanism at low voltages. At higher voltages, this mechanism is replaced by the rate-controlling tunneling via gap states in the forbidden gap.

  14. Characterization and improved solar light activity of vanadium doped TiO2/diatomite hybrid catalysts.

    Science.gov (United States)

    Wang, Bin; Zhang, Guangxin; Leng, Xue; Sun, Zhiming; Zheng, Shuilin

    2015-03-21

    V-doped TiO2/diatomite composite photocatalysts with different vanadium concentrations were synthesized by a modified sol-gel method. The diatomite was responsible for the well dispersion of TiO2 nanoparticles on the matrix and consequently inhibited the agglomeration. V-TiO2/diatomite hybrids showed red shift in TiO2 absorption edge with enhanced absorption intensity. Most importantly, the dopant energy levels were formed in the TiO2 bandgap due to V(4+) ions substituted to Ti(4+) sites. The 0.5% V-TiO2/diatomite photocatalyst displayed narrower bandgap (2.95 eV) compared to undoped sample (3.13 eV) and other doped samples (3.05 eV) with higher doping concentration. The photocatalytic activities of V doped TiO2/diatomite samples for the degradation of Rhodamine B under stimulated solar light illumination were significantly improved compared with the undoped sample. In our case, V(4+) ions incorporated in TiO2 lattice were responsible for increased visible-light absorption and electron transfer to oxygen molecules adsorbed on the surface of TiO2 to produce superoxide radicals ˙O2(-), while V(5+) species presented on the surface of TiO2 particles in the form of V2O5 contributed to e(-)-h(+) separation. In addition, due to the combination of diatomite as support, this hybrid photocatalyst could be separated from solution quickly by natural settlement and exhibited good reusability.

  15. Wide bandgap GaN-based semiconductors for spintronics

    Energy Technology Data Exchange (ETDEWEB)

    Pearton, S J [Department of Materials Science and Engineering, University of Florida, Gainesville, FL 32611 (United States); Abernathy, C R [Department of Materials Science and Engineering, University of Florida, Gainesville, FL 32611 (United States); Thaler, G T [Department of Materials Science and Engineering, University of Florida, Gainesville, FL 32611 (United States); Frazier, R M [Department of Materials Science and Engineering, University of Florida, Gainesville, FL 32611 (United States); Norton, D P [Department of Materials Science and Engineering, University of Florida, Gainesville, FL 32611 (United States); Ren, F [Department of Chemical Engineering, University of Florida, Gainesville, FL 32611 (United States); Park, Y D [CSCMR and School of Physics, Seoul National University, Seoul 151-747 (Korea, Republic of); Zavada, J M [US Army Research Office, Research Triangle Park, NC 27709 (United States); Buyanova, I A [Department of Physics and Measurement Technology, Linkoeping University, S-581 83 Linkoeping (Sweden); Chen, W M [Department of Physics and Measurement Technology, Linkoeping University, S-581 83 Linkoeping (Sweden); Hebard, A F [Department of Physics, University of Florida, Gainesville, FL 32611 (United States)

    2004-02-25

    Recent results on achieving ferromagnetism in transition-metal-doped GaN, AlN and related materials are discussed. The field of semiconductor spintronics seeks to exploit the spin of charge carriers in new generations of transistors, lasers and integrated magnetic sensors. There is strong potential for new classes of ultra-low-power, high speed memory, logic and photonic devices based on spintronics. The utility of such devices depends on the availability of materials with practical magnetic ordering temperatures and most theories predict that the Curie temperature will be a strong function of bandgap. We discuss the current state-of-the-art in producing room temperature ferromagnetism in GaN-based materials, the origins of the magnetism and its potential applications. (topical review)

  16. Semiconductor Metal-Organic Frameworks: Future Low-Bandgap Materials.

    Science.gov (United States)

    Usman, Muhammad; Mendiratta, Shruti; Lu, Kuang-Lieh

    2017-02-01

    Metal-organic frameworks (MOFs) with low density, high porosity, and easy tunability of functionality and structural properties, represent potential candidates for use as semiconductor materials. The rapid development of the semiconductor industry and the continuous miniaturization of feature sizes of integrated circuits toward the nanometer (nm) scale require novel semiconductor materials instead of traditional materials like silicon, germanium, and gallium arsenide etc. MOFs with advantageous properties of both the inorganic and the organic components promise to serve as the next generation of semiconductor materials for the microelectronics industry with the potential to be extremely stable, cheap, and mechanically flexible. Here, a perspective of recent research is provided, regarding the semiconducting properties of MOFs, bandgap studies, and their potential in microelectronic devices. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  17. Low voltage bandgap reference with closed loop curvature compensation

    Science.gov (United States)

    Tao, Fan; Bo, Du; Zheng, Zhang; Guoshun, Yuan

    2009-03-01

    A new low-voltage CMOS bandgap reference (BGR) that achieves high temperature stability is proposed. It feeds back the output voltage to the curvature compensation circuit that constitutes a closed loop circuit to cancel the logarithmic term of voltage VBE. Meanwhile a low voltage amplifier with the 0.5 μm low threshold technology is designed for the BGR. A high temperature stability BGR circuit is fabricated in the CSMC 0.5 μm CMOS technology. The measured result shows that the BGR can operate down to 1 V, while the temperature coefficient and line regulation are only 9 ppm/°C and 1.2 mV/V, respectively.

  18. Cavity quantum electrodynamics with three-dimensional photonic bandgap crystals

    CERN Document Server

    Vos, W L

    2015-01-01

    This paper gives an overview of recent work on three-dimensional (3D) photonic crystals with a "full and complete" 3D photonic band gap. We review five main aspects: 1) spontaneous emission inhibition, 2) spatial localization of light within a tiny nanoscale volume (aka "a nanobox for light"), 3) the introduction of a gain medium leading to thresholdless lasers, 4) breaking of the weak-coupling approximation of cavity QED, both in the frequency and in the time-domain, 5) decoherence, in particular the shielding of vacuum fluctuations by a 3D photonic bandgap. In addition, we list and evaluate all known photonic crystal structures with a demonstrated 3D band gap.

  19. Optical devices based on liquid crystal photonic bandgap fibers

    DEFF Research Database (Denmark)

    Alkeskjold, Thomas Tanggaard

    2005-01-01

    In this ph.d. work, an experimental and theoretical study on Liquid Crystal (LC) infiltrated Photonic Crystal Fibers (PCFs) has been carried out. PCFs usually, consists of an air/silica microstructure of air holes arranged in a triangular lattice surrounding a core defect defined by a missing air...... hole. The presence of a LC in the holes of the PCF transforms the fiber from a Total Internal Reflection (TIR) guiding type into a Photonic BandGap (PBG) guiding type, where light is confined to the silica core by coherent scattering from the LC-billed holes. The high dielectric and optical anisotropy...... of LCs combined with the unique waveguiding features of PBG fibers gives the LC filled PCFs unique tunable properties. PBG guidance has been demonstrated for different mesophases of LCs and various functional compact fibers has been demonstrated, which utilitzes the high thermo-optical and electro...

  20. One-dimensional photonic bandgap structure in abalone shell

    Institute of Scientific and Technical Information of China (English)

    LI Bo; ZHOU Ji; LI Longtu; LI Qi; HAN Shuo; HAO Zhibiao

    2005-01-01

    @@ Photonic bandgap (PBG) materials are periodic com- posites of dielectric materials in which electromagnetic waves of certain frequency range cannot propagate in any or a special direction. Recently, there has been great inter- est in synthetic PBG materials due to their ability in ma- nipulation of photons. Since 500 million years ago, the natural world has been exploiting photonic structures for specific biological purposes[1]. Different types of biologi- cal PBG materials have been discovered in recent years, such as the one-dimension PBG structure in the sea mouse Aphrodita[2], and the fruits Elaeocarpus[3,4]; two-dimension PBG structure in the male peacock Pavo muticus feathers[5], Indonesian male Papilio palinurus butterfly[6], Thaumantis diores butterfly[7] and the male Ancyluris meliboeus Fabricius butterflies[8]; and three-dimension PBG structure in the weevil Pachyrhynchus argus[9].

  1. MUTUAL COUPLING REDUCTION BETWEEN MICROSTRIP ANTENNAS USING ELECTROMAGNETIC BANDGAP STRUCTURE

    Directory of Open Access Journals (Sweden)

    G.N. Gaikwad

    2011-03-01

    Full Text Available When the number of antenna elements is placed in forming the arrays, mutual coupling between the antenna elements is a critical issue. This is particularly concern in phase array antennas. Mutual coupling is a potential source of performance degradation in the form of deviation of the radiation pattern from the desired one, gain reduction due to excitation of surface wave, increased side lobe levels etc. EBG (Electromagnetic Band Gap structure (also called as Photonic Bandgap Structure PBG not only enhances the performance of the patch antennas but also provides greater amount of isolation when placed between the microstrip arrays. This greatly reduces the mutual coupling between the antenna elements. The radiation efficiency, gain, antenna efficiency, VSWR, frequency, directivity etc greatly improves over the conventional patch antennas using EBG. The EBG structure and normal patch antenna is simulated using IE3D antenna simulation software.

  2. A Novel 2D Z-Shaped Electromagnetic Bandgap Structure

    Directory of Open Access Journals (Sweden)

    I. Iliev

    2015-02-01

    Full Text Available This paper researches a novel 2D Z-shaped Electromagnetic Band-Gap (EBG structure, its dispersion diagram and application field. Based on a transmission line model, the dispersion equation is derived and theoretically investigated. In order to validate theoretical results, a full wave analysis is performed and the electromagnetic properties of the structure are revealed. The theoretical results show good agreement with the full wave simulation results. The frequency response of the structure is compared to the well know structures of Jerusalem cross and patch EBG. The results show the applicability of the proposed 2D Z-shaped EBG in microstrip patch antennas, microstrip filters and high speed switching circuits, where the suppression of parasitic surface wave is required.

  3. Novel Photonic Bandgap Structure and Its Application in Amplifier

    Institute of Scientific and Technical Information of China (English)

    PANGYunbo; GAOBaoxin

    2003-01-01

    A novel compact photonic bandgap (PBG)structural element, which is etched in the ground plane of the microstrip line, is proposed in this paper. A forbid-den gap, which is about 200MHz wide, is measured at the center frequency of 8.6GHz. The measured results agree with finite difference time domain (FDTD) simulations. A harmonic-suppression amplifier is fabricated by utilizing this novel structural element. The suppression of the sec-ond order harmonic has been enhanced about 17dB when compared with a reference amplifier. Since no filters are needed and the structural element is etched in the ground plane, the whole circuit is compact.

  4. Low voltage bandgap reference with closed loop curvature compensation

    Institute of Scientific and Technical Information of China (English)

    Fan Tao; Du Bo; Zhang Zheng; Yuan Guoshun

    2009-01-01

    A new low-voltage CMOS bandgap reference (BGR) that achieves high temperature stability is proposed. It feeds back the output voltage to the curvature compensation circuit that constitutes a closed loop circuit to cancel the logarithmic term of voltage VBE. Meanwhile a low voltage amplifier with the 0.5μm low threshold technology is designed for the BGR. A high temperature stability BGR circuit is fabricated in the CSMC 0.5μm CMOS tech-nology. The measured result shows that the BGR can operate down to 1 V, while the temperature coefficient and line regulation are only 9 ppm/℃ and 1.2 mV/V, respectively.

  5. Perovskite/silicon-based heterojunction tandem solar cells with 14.8% conversion efficiency via adopting ultrathin Au contact

    Science.gov (United States)

    Fan, Lin; Wang, Fengyou; Liang, Junhui; Yao, Xin; Fang, Jia; Zhang, Dekun; Wei, Changchun; Zhao, Ying; Zhang, Xiaodan

    2017-01-01

    A rising candidate for upgrading the performance of an established narrow-bandgap solar technology without adding much cost is to construct the tandem solar cells from a crystalline silicon bottom cell and a high open-circuit voltage top cell. Here, we present a four-terminal tandem solar cell architecture consisting of a self-filtered planar architecture perovskite top cell and a silicon heterojunction bottom cell. A transparent ultrathin gold electrode has been used in perovskite solar cells to achieve a semi-transparent device. The transparent ultrathin gold contact could provide a better electrical conductivity and optical reflectance-scattering to maintain the performance of the top cell compared with the traditional metal oxide contact. The four-terminal tandem solar cell yields an efficiency of 14.8%, with contributions of the top (8.98%) and the bottom cell (5.82%), respectively. We also point out that in terms of optical losses, the intermediate contact of self-filtered tandem architecture is the uppermost problem, which has been addressed in this communication, and the results show that reducing the parasitic light absorption and improving the long wavelength range transmittance without scarifying the electrical properties of the intermediate hole contact layer are the key issues towards further improving the efficiency of this architecture device. Project supported by the International Cooperation Projects of the Ministry of Science and Technology (No. 2014DFE60170), the National Natural Science Foundation of China (Nos. 61474065, 61674084), the Tianjin Research Key Program of Application Foundation and Advanced Technology (No. 15JCZDJC31300), the Key Project in the Science & Technology Pillar Program of Jiangsu Province (No. BE2014147-3), and the 111 Project (No. B16027).

  6. Bandgap Engineering in High-Efficiency Multijunction Concentrator Cells

    Energy Technology Data Exchange (ETDEWEB)

    King, R. R.; Sherif, R. A.; Kinsey, G. S.; Kurtz, S.; Fetzer, C. M.; Edmondson, K. M.; Law, D. C.; Cotal, H. L.; Krut, D. D.; Ermer, J. H.; Karam, N. H.

    2005-08-01

    This paper discusses semiconductor device research paths under investigation with the aim of reaching the milestone efficiency of 40%. A cost analysis shows that achieving very high cell efficiencies is crucial for the realization of cost-effective photovoltaics, because of the strongly leveraging effect of efficiency on module packaging and balance-of systems costs. Lattice-matched (LM) GaInP/ GaInAs/ Ge 3-junction cells have achieved the highest independently confirmed efficiency at 175 suns, 25?C, of 37.3% under the standard AM1.5D, low-AOD terrestrial spectrum. Lattice-mismatched, or metamorphic (MM), materials offer still higher potential efficiencies, if the crystal quality can be maintained. Theoretical efficiencies well over 50% are possible for a MM GaInP/ 1.17-eV GaInAs/ Ge 3-junction cell limited by radiative recombination at 500 suns. The bandgap - open circuit voltage offset, (Eg/q) - Voc, is used as a valuable theoretical and experimental tool to characterize multijunction cells with subcell bandgaps ranging from 0.7 to 2.1 eV. Experimental results are presented for prototype 6-junction cells employing an active {approx}1.1-eV dilute nitride GaInNAs subcell, with active-area efficiency greater than 23% and over 5.3 V open-circuit voltage under the 1-sun AM0 space spectrum. Such cell designs have theoretical efficiencies under the terrestrial spectrum at 500 suns concentration exceeding 55% efficiency, even for lattice-matched designs.

  7. A Narrow View of Reading Promotes Comprehension

    National Research Council Canada - National Science Library

    Alan G Kamhi

    2007-01-01

      In sum, embracing the narrow view of reading will promote differentiated assessment of reading and content-specific knowledge that will not only eliminate the reading crisis, but also focus attention...

  8. Device Physics of Narrow Gap Semiconductors

    CERN Document Server

    Chu, Junhao

    2010-01-01

    Narrow gap semiconductors obey the general rules of semiconductor science, but often exhibit extreme features of these rules because of the same properties that produce their narrow gaps. Consequently these materials provide sensitive tests of theory, and the opportunity for the design of innovative devices. Narrow gap semiconductors are the most important materials for the preparation of advanced modern infrared systems. Device Physics of Narrow Gap Semiconductors offers descriptions of the materials science and device physics of these unique materials. Topics covered include impurities and defects, recombination mechanisms, surface and interface properties, and the properties of low dimensional systems for infrared applications. This book will help readers to understand not only the semiconductor physics and materials science, but also how they relate to advanced opto-electronic devices. The last chapter applies the understanding of device physics to photoconductive detectors, photovoltaic infrared detector...

  9. Narrow deeply bound K- atomic states

    Science.gov (United States)

    Friedman, E.; Gal, A.

    1999-07-01

    Using optical potentials fitted to a comprehensive set of strong interaction level shifts and widths in K- atoms, we predict that the K- atomic levels which are inaccessible in the atomic cascade process are generally narrow, spanning a range of widths about 50-1500 keV over the entire periodic table. The mechanism for this narrowing is different from the mechanism for narrowing of pionic atom levels. Examples of such `deeply bound' K- atomic states are given, showing that in many cases these states should be reasonably well resolved. Several reactions which could be used to form these `deeply bound' states are mentioned. Narrow deeply bound states are expected also in overlinep atoms.

  10. Anomalous band gap behavior in mixed Sn and Pb perovskites enables broadening of absorption spectrum in solar cells.

    Science.gov (United States)

    Hao, Feng; Stoumpos, Constantinos C; Chang, Robert P H; Kanatzidis, Mercouri G

    2014-06-04

    Perovskite-based solar cells have recently been catapulted to the cutting edge of thin-film photovoltaic research and development because of their promise for high-power conversion efficiencies and ease of fabrication. Two types of generic perovskites compounds have been used in cell fabrication: either Pb- or Sn-based. Here, we describe the performance of perovskite solar cells based on alloyed perovskite solid solutions of methylammonium tin iodide and its lead analogue (CH3NH3Sn(1-x)Pb(x)I3). We exploit the fact that, the energy band gaps of the mixed Pb/Sn compounds do not follow a linear trend (the Vegard's law) in between these two extremes of 1.55 and 1.35 eV, respectively, but have narrower bandgap (Pb ratio. Our results show that CH3NH3Sn(0.5)Pb(0.5)I3 has the broadest light absorption and highest short-circuit photocurrent density ~20 mA cm(-2) (obtained under simulated full sunlight of 100 mW cm(-2)).

  11. Hydrogen-doped Brookite TiO2 Nanobullets Array as a Novel Photoanode for Efficient Solar Water Splitting

    Science.gov (United States)

    Choi, Mingi; Lee, June Ho; Jang, Youn Jeong; Kim, Donghyung; Lee, Jae Sung; Jang, Hyun Myung; Yong, Kijung

    2016-01-01

    As a representative photocatalyst for photoelectrochemical solar water splitting, TiO2 has been intensively studied but most researches have focused on the rutile and anatsase phases because brookite, another important crystalline polymorph of TiO2, rarely exists in nature and is difficult to synthesize. In this work, hydrogen doped brookite (H:brookite) nanobullet arrays were synthesized via a well-designed solution reaction for the first time. H:brookite shows highly improved PEC properties with excellent stability, enhanced photocurrent, and significantly high Faradaic efficiency for overall solar water splitting. To support the experimental data, ab initio density functional theory calculations were also conducted. At the interstitial doping site that has minimum formation energy, the hydrogen atoms act as shallow donors and exist as H+. which has the minimum formation energy among three states of hydrogen (H+. H0, and H−). The calculated density of states of H:brookite shows a narrowed bandgap and an increased electron density compared to the pristine brookite. The combined experimental and theoretical results provide frameworks for the exploration of the PEC properties of doped brookite and extend our knowledge regarding the undiscovered properties of brookite of TiO2. PMID:27782198

  12. Effect of tellurium deposition rate on the properties of Cu-In-Te based thin films and solar cells

    Science.gov (United States)

    Mise, Takahiro; Nakada, Tokio

    2011-01-01

    To investigate the effects of tellurium (Te) deposition rate on the properties of Cu-In-Te based thin films (Cu/In=0.30-0.31), the films were grown on both bare and Mo-coated soda-lime glass substrates at 200 °C by co-evaporation using a molecular beam epitaxy system. The microstructural properties were examined by means of scanning electron microscopy and X-ray diffraction. The crystalline quality of the films was improved with increase in the deposition rate of Te, and exhibited a single CuIn 3Te 5 phase with a highly preferred (1 1 2) orientation. Te-deficient film (Te/(Cu+In)=1.07) grown with a low Te deposition rate showed a narrow bandgap of 0.99 eV at room temperature. The solar cell performance was affected by the deposition rate of Te. The best solar cell fabricated using CuIn 3Te 5 thin films grown with the highest deposition rate of Te (2.6 nm/s) yielded a total area (0.50 cm 2) efficiency of 4.4% ( Voc=309 mV, Jsc=28.0 mA/cm 2, and FF=0.509) without light soaking.

  13. Effect of nonlinear physical phenomena on the photovoltaic effect in silicon p +-n-n + solar cells

    Science.gov (United States)

    Mnatsakanov, T. T.; Shuman, V. B.; Pomortseva, L. I.; Schröder, D.; Schlögl, A.

    2000-03-01

    The influence of the combined effects of high injection level and heavy doping on the characteristics of silicon p +-n-n + solar cells is examined. The total amount of nonlinear physical phenomena (Auger recombination, electron-hole scattering, band-gap narrowing, charge carrier lifetime and transport coefficient reduction in the heavily doped layers of the structure) is taken into account. It has been established that a combined process which includes the generated charge carrier overflowing from n-base layer to highly doped n +-type and p +-type layers of the structure and their subsequent recombination in these highly doped layers, proves to be of great importance in silicon solar cells. The influence of electron-hole scattering on charge carrier transport in the highly doped n +-type and p +-type layers has been investigated for the first time. It has been found that minority carrier complete drag phenomenon results in a significant decrease of n +-type and p +-type layer saturation currents.

  14. Hydrogen-doped Brookite TiO2 Nanobullets Array as a Novel Photoanode for Efficient Solar Water Splitting

    Science.gov (United States)

    Choi, Mingi; Lee, June Ho; Jang, Youn Jeong; Kim, Donghyung; Lee, Jae Sung; Jang, Hyun Myung; Yong, Kijung

    2016-10-01

    As a representative photocatalyst for photoelectrochemical solar water splitting, TiO2 has been intensively studied but most researches have focused on the rutile and anatsase phases because brookite, another important crystalline polymorph of TiO2, rarely exists in nature and is difficult to synthesize. In this work, hydrogen doped brookite (H:brookite) nanobullet arrays were synthesized via a well-designed solution reaction for the first time. H:brookite shows highly improved PEC properties with excellent stability, enhanced photocurrent, and significantly high Faradaic efficiency for overall solar water splitting. To support the experimental data, ab initio density functional theory calculations were also conducted. At the interstitial doping site that has minimum formation energy, the hydrogen atoms act as shallow donors and exist as H+. which has the minimum formation energy among three states of hydrogen (H+. H0, and H-). The calculated density of states of H:brookite shows a narrowed bandgap and an increased electron density compared to the pristine brookite. The combined experimental and theoretical results provide frameworks for the exploration of the PEC properties of doped brookite and extend our knowledge regarding the undiscovered properties of brookite of TiO2.

  15. Ab initio design of nanostructures for solar energy conversion: a case study on silicon nitride nanowire.

    Science.gov (United States)

    Pan, Hui

    2014-01-01

    Design of novel materials for efficient solar energy conversion is critical to the development of green energy technology. In this work, we present a first-principles study on the design of nanostructures for solar energy harvesting on the basis of the density functional theory. We show that the indirect band structure of bulk silicon nitride is transferred to direct bandgap in nanowire. We find that intermediate bands can be created by doping, leading to enhancement of sunlight absorption. We further show that codoping not only reduces the bandgap and introduces intermediate bands but also enhances the solubility of dopants in silicon nitride nanowires due to reduced formation energy of substitution. Importantly, the codoped nanowire is ferromagnetic, leading to the improvement of carrier mobility. The silicon nitride nanowires with direct bandgap, intermediate bands, and ferromagnetism may be applicable to solar energy harvesting.

  16. Narrow linewidth pulsed optical parametric oscillator

    Indian Academy of Sciences (India)

    S Das

    2010-11-01

    Tunable narrow linewidth radiation by optical parametric oscillation has many applications, particularly in spectroscopic investigation. In this paper, different techniques such as injection seeding, use of spectral selecting element like grating, grating and etalon in combination, grazing angle of incidence, entangled cavity configuration and type-II phase matching have been discussed for generating tunable narrow linewidth radiation by singly resonant optical parametric oscillation process.

  17. A three solar cell system based on a self-supporting, transparent AlGaAs top solar cell

    Science.gov (United States)

    Negley, Gerald H.; Rhoads, Sandra L.; Terranova, Nancy E.; Mcneely, James B.; Barnett, Allen M.

    1989-01-01

    Development of a three solar cell stack can lead to practical efficiencies greater than 30 percent (1x,AM0). A theoretical efficiency limitation of 43.7 percent at AM0 and one sun is predicted by this model. Including expected losses, a practical system efficiency of 36.8 percent is anticipated. These calculations are based on a 1.93eV/1.43eV/0.89eV energy band gap combination. AlGaAs/GaAs/GaInAsP materials can be used with a six-terminal wiring configuration. The key issues for multijunction solar cells are the top and middle solar cell performance and the sub-bandgap transparency. AstroPower has developed a technique to fabricate AlGaAs solar cells on rugged, self-supporting, transparent AlGaAs substrates. Top solar cell efficiencies greater than 11 percent AM0 have been achieved. State-of-the-art GaAs or InP devices will be used for the middle solar cell. GaInAsP will be used to fabricate the bottom solar cell. This material is lattice-matched to InP and offers a wide range of bandgaps for optimization of the three solar cell stack. Liquid phase epitaxy is being used to grow the quaternary material. Initial solar cells have shown open-circuit voltages of 462 mV for a bandgap of 0.92eV. Design rules for the multijunction three solar cell stack are discussed. The progress in the development of the self-supporting AlGaAs top solar cell and the GaInAsP bottom solar cell is presented.

  18. Electrically tunable Yb-doped fiber laser based on a liquid crystal photonic bandgap fiber device

    DEFF Research Database (Denmark)

    Olausson, Christina Bjarnal Thulin; Scolari, Lara; Wei, Lei

    2010-01-01

    We demonstrate electrical tunability of a fiber laser using a liquid crystal photonic bandgap fiber. Tuning of the laser is achieved by combining the wavelength filtering effect of a tunable liquid crystal photonic bandgap fiber device with an ytterbium-doped photonic crystal fiber. We fabricate...... an all-spliced laser cavity based on the liquid crystal photonic bandgap fiber mounted on a silicon assembly, a pump/signal combiner with single-mode signal feed-through and an ytterbium-doped photonic crystal fiber. The laser cavity produces a single-mode output and is tuned in the range 1040-1065 nm...

  19. 167 W, power scalable ytterbium-doped photonic bandgap fiber amplifier at 1178nm

    DEFF Research Database (Denmark)

    Olausson, Christina Bjarnal Thulin; Shirakawa, A.; Chen, M.

    2010-01-01

    An ytterbium-doped photonic bandgap fiber amplifier operating at the long wavelength edge of the ytterbium gain band is investigated for high power amplification. The spectral filtering effect of the photonic bandgap efficiently suppresses amplified spontaneous emission at the conventional...... ytterbium gain wavelengths and thus enables high power amplification at 1178 nm. A record output power of 167 W, a slope efficiency of 61% and 15 dB saturated gain at 1178 nm have been demonstrated using the ytterbium-doped photonic bandgap fiber....

  20. Highly tunable large core single-mode liquid crystal photonic bandgap fiber

    DEFF Research Database (Denmark)

    Alkeskjold, Thomas Tanggaard; Lægsgaard, Jesper; Bjarklev, Anders Overgaard;

    2006-01-01

    We demonstrate a highly tunable photonic bandgap fiber, which has a large-core diameter of 25 mu m and an effective mode area of 440 mu m(2). The tunability is achieved by infiltrating the air holes of a photonic crystal fiber with an optimized liquid-crystal mixture having a large temperature...... gradient of the refractive indices at room temperature. A bandgap tuning sensitivity of 27 nm/degrees C is achieved at room temperature. The insertion loss is estimated to be less than 0.5 dB and caused mainly by coupling loss between the index-guided mode and the bandgap-guided mode. (c) 2006 Optical...

  1. Synthesis and Characterization of Small Band-gap Conjugated Polymers - Poly(pyrrolyl methines)

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    A kind of small band-gap conjugated polymers-poly (pyrrolyl methines) and their precursors-(poly pyrrolyl methanes) have been synthesized by a simple method and characterized by 1HNMR, FT-IR, TGA and UV-Vis. These polymers can be dissolved in high polar solvents such as DMSO, DMF or NMP. The results reveals that the band-gap of the synthesized conjugated polymers are in the range of 0.96~1.14 eV and they all belong to the small band-gap polymers. The conductivity of doped products with iodine is in the range of semiconductor.

  2. Simple way to make Anatase TiO2 films on FTO glass for promising solar cells

    OpenAIRE

    Raghavender, A. T.; Samantilleke, A. P.; Sá,Pedro; Almeida, B. G.; Vasilevskiy, Mikhail; Nguyen Hoa Hong

    2011-01-01

    TiO2 is a wide bandgap semiconductor material used as the photo anode in dye sensitized solar cells (DSSC). The fabrication of TiO2 on conductive glass substrates plays an important role in the solar cell efficiency, since the thickness of the TiO2 coating affects the transmission, photoconductive properties and the efficiency of solar cells. The uncorrected transmission in our fabricated films is as high as 80%, and the bandgap obtained is similar to that of bulk anatase TiO2, co...

  3. The strain induced band gap modulation from narrow gap semiconductor to half-metal on Ti2CrGe: A first principles study

    Directory of Open Access Journals (Sweden)

    Jia Li

    2015-11-01

    Full Text Available The Heusler alloy Ti2CrGe is a stable L21 phase with antiferromagnetic ordering. With band-gap energy (∼ 0.18 eV obtained from a first-principles calculation, it belongs to the group of narrow band gap semiconductor. The band-gap energy decreases with increasing lattice compression and disappears until a strain of −5%; moreover, gap contraction only occurs in the spin-down states, leading to half-metallic character at the −5% strain. The Ti1, Ti2, and Cr moments all exhibit linear changes in behavior within strains of −5%– +5%. Nevertheless, the total zero moment is robust for these strains. The imaginary part of the dielectric function for both up and down spin states shows a clear onset energy, indicating a corresponding electronic gap for the two spin channels.

  4. Band gap narrowing in ferroelectric KNbO3-Bi(Yb,Me)O3 (Me=Fe or Mn) ceramics

    Science.gov (United States)

    Pascual-Gonzalez, Cristina; Schileo, Giorgio; Feteira, Antonio

    2016-09-01

    The direct optical bandgap in ferroelectric KNbO3-Bi(Yb,Me)O3 (Me = Fe or Mn) ceramics fabricated by the solid state reaction method varies from 3.2 eV for KNbO3 down to 2.2 eV for 0.95KNbO3-0.05BiYbO3, as revealed by optical spectroscopic ellipsometry. This narrowing of bandgap is accompanied by an apparent increase of the room-temperature relative permittivity from 320 for KNbO3 to 900 for 0.95KNbO3-0.05BiYbO3. All compositions studied exhibit dielectric anomalies associated with structural phase transitions, and their ferroelectric nature is corroborated by the presence of a sharp mixed mode (at ˜190 cm-1) and by a Fano-type resonant dip in their Raman spectra.

  5. 结构参数对二维Archimedes A7晶格光子晶体禁带的影响%Effects of structure parameters on the bandgap of two dimensional Archimedes A7 photonic crystals

    Institute of Scientific and Technical Information of China (English)

    杨毅彪; 王伟军; 费宏明; 梁伟; 王云才

    2012-01-01

    利用平面波展开法对空气背景中介质圆柱和方柱构造的二维Archimedes A7晶格光子晶体的禁带结构随介质折射率、填充比的变化关系进行了研究,并进一步计算了介质方柱的旋转角度对完全光子禁带宽度的影响.研究发现,介质圆柱构造的Archimedes A7晶格结构在介质柱折射率最低为n=2.40时出现完全光子禁带,当n=2.60时禁带宽度达到最大值.介质方柱构造的Archimedes A7晶格结构在介质柱折射率n=3.80时完全禁带宽度达到最大值,且随着折射率的增加禁带宽度变化很小;在介质方柱折射率恒定情况下,其最大禁带宽度与旋转角度无关,但旋转后出现完全禁带的填充比范围明显扩大.%Plane wave expansion method is introduced to simulate the band structures of two-dimensional photonic crystals made of Archimedes A7 lattice of circular and square dielectric rod in air. The bandgaps of Archimedes A7 lattice with dielectric rods is also discussed as functions of the refractive index, filling fraction and rotation angle. The results show that the complete bandgap can be obtained when the refractive index is greater than 2.40. The width of complete bandgap reaches the maximum when the dielectric refractive index of the circular rod is equal to 2.60. For the Archimedes A7 lattice of square dielectric rod, the complete bandgap reaches the maximum when the dielectric refractive index equals 3. 80. The maximum complete bandgap changes in a narrow range as the refractive index increases. When the rotation angle of the square dielectric rods changes, the maximum bandgap keeps constant for a fixed refractive index. However after the change of rotation angle, the complete bandgap appears in a large scale of the filling fraction.

  6. Review of Polymer, Dye-Sensitized, and Hybrid Solar Cells

    Directory of Open Access Journals (Sweden)

    S. N. F. Mohd-Nasir

    2014-01-01

    Full Text Available The combination of inorganic nanoparticles semiconductor, conjugated polymer, and dye-sensitized in a layer of solar cell is now recognized as potential application in developing flexible, large area, and low cost photovoltaic devices. Several conjugated low bandgap polymers, dyes, and underlayer materials based on the previous studies are quoted in this paper, which can provide guidelines in designing low cost photovoltaic solar cells. All of these materials are designed to help harvest more sunlight in a wider range of the solar spectrum besides enhancing the rate of charge transfer in a device structure. This review focuses on developing solid-state dye-synthesized, polymer, and hybrid solar cells.

  7. Detailed balance limit efficiency of silicon intermediate band solar cells

    Institute of Scientific and Technical Information of China (English)

    Cao Quan; Ma Zhi-Hua; Xue Chun-Lai; Zuo Yu-Hua; Wang Qi-Ming

    2011-01-01

    The detailed balance method is used to study the potential of the intermediate band solar cell (IBSC),which can improve the efficiency of the Si-based solar cell with a bandgap between 1.1 eV to 1.7 eV. It shows that a crystalline silicon solar cell with an intermediate band located at 0.36 eV below the conduction band or above the valence band can reach a limiting efficiency of 54% at the maximum light concentration,improving greatly than 40.7% of the Shockley-Queisser limit for the single junction Si solar cell. The simulation also shows that the limiting efficiency of the siliconbased solar cell increases as the bandgap increases from 1.1 eV to 1.7 eV,and the amorphous Si solar cell with a bandgap of 1.7 eV exhibits a radiative limiting efficiency of 62.47%,having a better potential.

  8. Radiative thermal escape in intermediate band solar cells

    Directory of Open Access Journals (Sweden)

    A. Luque

    2011-06-01

    Full Text Available To achieve high efficiency, the intermediate band (IB solar cell must generate photocurrent from sub-bandgap photons at a voltage higher than that of a single contributing sub-bandgap photon. To achieve the latter, it is necessary that the IB levels be properly isolated from the valence and conduction bands. We prove that this is not the case for IB cells formed with the confined levels of InAs quantum dots (QDs in GaAs grown so far due to the strong density of internal thermal photons at the transition energies involved. To counteract this, the QD must be smaller.

  9. Refractive index extraction and thickness optimization of Cu2ZnSnSe4 thin film solar cells

    NARCIS (Netherlands)

    ElAnzeery, H.; El Daif, O.; Buffière, M.; Oueslati, S.; Ben Messaoud, K.; Agten, D.; Brammertz, G.; Guindi, R.; Kniknie, B.; Meuris, M.; Poortmans, J.

    2015-01-01

    Cu2nSnSe4 (CZTSe) thin film solar cells are promising emergent photovoltaic technologies based on low-bandgap absorber layer with high absorption coefficient. To reduce optical losses in such devices and thus improve their efficiency, numerical simulations of CZTSe solar cells optical characteristic

  10. Fringe structures and tunable bandgap width of 2D boron nitride nanosheets

    Directory of Open Access Journals (Sweden)

    Peter Feng

    2014-07-01

    Full Text Available We report studies of the surface fringe structures and tunable bandgap width of atomic-thin boron nitride nanosheets (BNNSs. BNNSs are synthesized by using digitally controlled pulse deposition techniques. The nanoscale morphologies of BNNSs are characterized by using scanning electron microscope (SEM, and transmission electron microscopy (TEM. In general, the BNNSs appear microscopically flat in the case of low temperature synthesis, whereas at high temperature conditions, it yields various curved structures. Experimental data reveal the evolutions of fringe structures. Functionalization of the BNNSs is completed with hydrogen plasma beam source in order to efficiently control bandgap width. The characterizations are based on Raman scattering spectroscopy, X-ray diffraction (XRD, and FTIR transmittance spectra. Red shifts of spectral lines are clearly visible after the functionalization, indicating the bandgap width of the BNNSs has been changed. However, simple treatments with hydrogen gas do not affect the bandgap width of the BNNSs.

  11. SSPA's Using Reduced Conduction Angle Techniques on Wide-Bandgap Devices for Ultra High Efficiency Project

    Data.gov (United States)

    National Aeronautics and Space Administration — A novel approach is proposed for very efficient, very reliable, low weight, wide-bandgap medium power SSPAs for Space applications operating at 400 MHz and 8GHz.

  12. Optical bandgap of ultra-thin amorphous silicon films deposited on crystalline silicon by PECVD

    National Research Council Canada - National Science Library

    Abdulraheem, Yaser; Gordon, Ivan; Bearda, Twan; Meddeb, Hosny; Poortmans, Jozef

    2014-01-01

    ...) in a wavelength range from 250 nm to 850 nm. The data was fitted to a Tauc-Lorentz optical model and the fitting parameters were extracted and used to compute the refractive index, extinction coefficient and optical bandgap...

  13. MoS2/MX2 heterobilayers: bandgap engineering via tensile strain or external electrical field

    Science.gov (United States)

    Lu, Ning; Guo, Hongyan; Li, Lei; Dai, Jun; Wang, Lu; Mei, Wai-Ning; Wu, Xiaojun; Zeng, Xiao Cheng

    2014-02-01

    We have performed a comprehensive first-principles study of the electronic and magnetic properties of two-dimensional (2D) transition-metal dichalcogenide (TMD) heterobilayers MX2/MoS2 (M = Mo, Cr, W, Fe, V; X = S, Se). For M = Mo, Cr, W; X = S, Se, all heterobilayers show semiconducting characteristics with an indirect bandgap with the exception of the WSe2/MoS2 heterobilayer which retains the direct-bandgap character of the constituent monolayer. For M = Fe, V; X = S, Se, the MX2/MoS2 heterobilayers exhibit metallic characters. Particular attention of this study has been focused on engineering the bandgap of the TMD heterobilayer materials via application of either a tensile strain or an external electric field. We find that with increasing either the biaxial or uniaxial tensile strain, the MX2/MoS2 (M = Mo, Cr, W; X = S, Se) heterobilayers can undergo a semiconductor-to-metal transition. For the WSe2/MoS2 heterobilayer, a direct-to-indirect bandgap transition may occur beyond a critical biaxial or uniaxial strain. For M (=Fe, V) and X (=S, Se), the magnetic moments of both metal and chalcogen atoms are enhanced when the MX2/MoS2 heterobilayers are under a biaxial tensile strain. Moreover, the bandgap of MX2/MoS2 (M = Mo, Cr, W; X = S, Se) heterobilayers can be reduced by the vertical electric field. For two heterobilayers MSe2/MoS2 (M = Mo, Cr), PBE calculations suggest that the indirect-to-direct bandgap transition may occur under an external electric field. The transition is attributed to the enhanced spontaneous polarization. The tunable bandgaps in general and possible indirect-direct bandgap transitions due to tensile strain or external electric field make the TMD heterobilayer materials a viable candidate for optoelectronic applications.We have performed a comprehensive first-principles study of the electronic and magnetic properties of two-dimensional (2D) transition-metal dichalcogenide (TMD) heterobilayers MX2/MoS2 (M = Mo, Cr, W, Fe, V; X = S, Se). For

  14. Bandgaps of the Chalcogenide Glass Hollow-Core Photonic Crystal Fiber

    Science.gov (United States)

    Li, Shu-Guang; Zhou, Hong-Song; Yin, Guo-Bing

    2011-11-01

    Bandgaps of chalcogenide glass hollow-core photonic crystal fibers (GLS HC-PCFs) are analyzed by using the plane-wave expansion method. A mid-infrared laser can propagate in these low confinement loss fibers when the wavelength falls into the bandgaps. For enlarging the bandgap width, an improved GLS HC-PCF is put forward, the normalized frequency kΛ of the improved fiber is from 7.2 to 8.5 in its first bandgap. The improved GLS HC-PCF with pitch of 4.2 μm can transmit the lights with wavelengths ranging from 3.1 μm to 3.7 μm.

  15. Vibration band-gap properties of three-dimensional Kagome lattices using the spectral element method

    Science.gov (United States)

    Wu, Zhi-Jing; Li, Feng-Ming; Zhang, Chuanzeng

    2015-04-01

    The spectral element method (SEM) is extended to investigate the vibration band-gap properties of three-dimensional (3D) Kagome lattices. The dynamic stiffness matrix of the 3D element which contains bending, tensional and torsional components is derived. The spectral equations of motion of the whole 3D Kagome lattice are then established. Comparing with frequency-domain solutions calculated by the finite element method (FEM), the accuracy and the feasibility of the SEM solutions are verified. It can be shown that the SEM is suitable for analyzing the vibration band-gap properties. Due to the band-gap characteristics, the periodic 3D Kagome lattice has the performance of vibration isolation. The influences of the structural and material parameters on the vibration band-gaps are discussed and a new type of 3D Kagome lattice is designed to obtain the improved vibration isolation capability.

  16. Microresonator and associated method for producing and controlling photonic signals with a photonic bandgap delay apparatus

    Science.gov (United States)

    Fork, Richard Lynn (Inventor); Jones, Darryl Keith (Inventor); Keys, Andrew Scott (Inventor)

    2000-01-01

    By applying a photonic signal to a microresonator that includes a photonic bandgap delay apparatus having a photonic band edge transmission resonance at the frequency of the photonic signal, the microresonator imparts a predetermined delay to the photonic signal. The photonic bandgap delay apparatus also preferably has a photonic band edge transmission resonance bandwidth which is at least as wide as the bandwidth of the photonic signal such that a uniform delay is imparted over the entire bandwidth of the photonic signal. The microresonator also includes a microresonator cavity, typically defined by a pair of switchable mirrors, within which the photonic bandgap delay apparatus is disposed. By requiring the photonic signal to oscillate within the microresonator cavity so as to pass through the photonic bandgap delay apparatus several times, the microresonator can controllably impart an adjustable delay to the photonic signal.

  17. Bandgap engineering of graphene decorated with randomly distributed ZnO nano-seed

    Science.gov (United States)

    Al-Amin, Chowdhury; Vabbina, Phani Kiran; Karabiyik, Mustafa; Sinha, Raju; Pala, Nezih

    2016-05-01

    In this paper, we have experimentally demonstrated the engineering of semi-metal single layer CVD Graphene's bandgap by decorating with randomly distributed ZnO nano-seed grown by sonication of Zinc acetate dehydrate. The proximity of nanoparticles and Graphene breaks Graphene's sublattice symmetry and opens-up a bandgap. The 2-D/G ratio of Raman spectroscopy of decorated Graphene along with a peak at 432.39 cm-1 confirmed presence of ZnO on single layer Graphene. The introduced bandgap was measured from the slope of Arrhenius plot. Graphene with significant bandgap introduced by the proposed methods could be used for devices intended for digital and logic applications.

  18. Gap formation and guided modes in photonic bandgap fibres with high-index rods

    DEFF Research Database (Denmark)

    Lægsgaard, Jesper

    2004-01-01

    Photonic bandgap fibres fabricated by infiltrating the holes of a microstructured optical fibre with high-index material are investigated numerically in the low- and intermediate-frequency regime. Bandgaps, transmission windows and the distribution of field energy between high- and low-index regi......Photonic bandgap fibres fabricated by infiltrating the holes of a microstructured optical fibre with high-index material are investigated numerically in the low- and intermediate-frequency regime. Bandgaps, transmission windows and the distribution of field energy between high- and low......-index regions are investigated. It is shown that the numerical results found can be rationalized in a simple way by considering the properties of guided modes in a conventional step-index fibre....

  19. Solar Cells Using Quantum Funnels

    KAUST Repository

    Kramer, Illan J.

    2011-09-14

    Colloidal quantum dots offer broad tuning of semiconductor bandstructure via the quantum size effect. Devices involving a sequence of layers comprised of quantum dots selected to have different diameters, and therefore bandgaps, offer the possibility of funneling energy toward an acceptor. Here we report a quantum funnel that efficiently conveys photoelectrons from their point of generation toward an intended electron acceptor. Using this concept we build a solar cell that benefits from enhanced fill factor as a result of this quantum funnel. This concept addresses limitations on transport in soft condensed matter systems and leverages their advantages in large-area optoelectronic devices and systems. © 2011 American Chemical Society.

  20. Dye-Sensitized Solar Cell with Integrated Triplet-Triplet Annihilation Upconversion System.

    Science.gov (United States)

    Nattestad, Andrew; Cheng, Yuen Yap; MacQueen, Rowan W; Schulze, Tim F; Thompson, Fletcher W; Mozer, Attila J; Fückel, Burkhard; Khoury, Tony; Crossley, Maxwell J; Lips, Klaus; Wallace, Gordon G; Schmidt, Timothy W

    2013-06-20

    Photon upconversion (UC) by triplet-triplet annihilation (TTA-UC) is employed in order to enhance the response of solar cells to sub-bandgap light. Here, we present the first report of an integrated photovoltaic device, combining a dye-sensitized solar cell (DSC) and TTA-UC system. The integrated device displays enhanced current under sub-bandgap illumination, resulting in a figure of merit (FoM) under low concentration (3 suns), which is competitive with the best values recorded to date for nonintegrated systems. Thus, we demonstrate both the compatibility of DSC and TTA-UC and a viable method for device integration.

  1. Gap between active and passive solar heating

    Energy Technology Data Exchange (ETDEWEB)

    Balcomb, J.D.

    1985-01-01

    The gap between active and passive solar could hardly be wider. The reasons for this are discussed and advantages to narrowing the gap are analyzed. Ten years of experience in both active and passive systems are reviewed, including costs, frequent problems, performance prediction, performance modeling, monitoring, and cooling concerns. Trends are analyzed, both for solar space heating and for service water heating. A tendency for the active and passive technologies to be converging is observed. Several recommendations for narrowing the gap are presented.

  2. Thermal modeling of wide bandgap materials for power MOSFETs

    Science.gov (United States)

    Manandhar, Mahesh B.; Matin, Mohammad A.

    2016-09-01

    This paper investigates the thermal performance of different wide bandgap (WBG) materials for their applicability as semiconductor material in power electronic devices. In particular, Silicon Carbide (SiC) and Gallium Nitride (GaN) are modeled for this purpose. These WBG materials have been known to show superior intrinsic material properties as compared to Silicon (Si), such as higher carrier mobility, lower electrical and thermal resistance. These unique properties have allowed for them to be used in power devices that can operate at higher voltages, temperatures and switching speeds with higher efficiencies. Digital prototyping of power devices have facilitated inexpensive and flexible methods for faster device development. The commercial simulation software COMSOL Multiphysics was used to simulate a 2-D model of MOSFETs of these WBG materials to observe their thermal performance under different voltage and current operating conditions. COMSOL is a simulation software that can be used to simulate temperature changes due to Joule heating in the case of power MOSFETs. COMSOL uses Finite Element/Volume Analysis methods to solve for variables in complex geometries where multiple material properties and physics are involved. The Semiconductor and Heat Transfer with Solids modules of COMSOL were used to study the thermal performance of the MOSFETs in steady state conditions. The results of the simulations for each of the two WBG materials were compared with that of Silicon to determine relative stability and merit of each material.

  3. Research on micro-sized acoustic bandgap structures.

    Energy Technology Data Exchange (ETDEWEB)

    Fleming, James Grant; McCormick, Frederick Bossert; Su, Mehmet F.; El-Kady, Ihab Fathy; Olsson, Roy H., III; Tuck, Melanie R.

    2010-01-01

    Phononic crystals (or acoustic crystals) are the acoustic wave analogue of photonic crystals. Here a periodic array of scattering inclusions located in a homogeneous host material forbids certain ranges of acoustic frequencies from existence within the crystal, thus creating what are known as acoustic (or phononic) bandgaps. The vast majority of phononic crystal devices reported prior to this LDRD were constructed by hand assembling scattering inclusions in a lossy viscoelastic medium, predominantly air, water or epoxy, resulting in large structures limited to frequencies below 1 MHz. Under this LDRD, phononic crystals and devices were scaled to very (VHF: 30-300 MHz) and ultra (UHF: 300-3000 MHz) high frequencies utilizing finite difference time domain (FDTD) modeling, microfabrication and micromachining technologies. This LDRD developed key breakthroughs in the areas of micro-phononic crystals including physical origins of phononic crystals, advanced FDTD modeling and design techniques, material considerations, microfabrication processes, characterization methods and device structures. Micro-phononic crystal devices realized in low-loss solid materials were emphasized in this work due to their potential applications in radio frequency communications and acoustic imaging for medical ultrasound and nondestructive testing. The results of the advanced modeling, fabrication and integrated transducer designs were that this LDRD produced the 1st measured phononic crystals and phononic crystal devices (waveguides) operating in the VHF (67 MHz) and UHF (937 MHz) frequency bands and established Sandia as a world leader in the area of micro-phononic crystals.

  4. Angle-dependent bandgap engineering in gated graphene superlattices

    Energy Technology Data Exchange (ETDEWEB)

    García-Cervantes, H.; Sotolongo-Costa, O. [Centro de Investigación en Ciencias, IICBA, Universidad Autónoma del Estado de Morelos, Av. Universidad 1001, Col. Chamilpa, 62209 Cuernavaca, Morelos, México (Mexico); Gaggero-Sager, L. M. [CIICAp, IICBA, Universidad Autónoma del Estado de Morelos, Av. Universidad 1001, Col. Chamilpa, 62209 Cuernavaca, Morelos, México (Mexico); Naumis, G. G. [Instituto Física, Depto. de Física-Química, Universidad Nacional Autónoma de México (UNAM). Apdo. Postal 20-364, 01000, México D.F., México (Mexico); Rodríguez-Vargas, I., E-mail: isaac@fisica.uaz.edu.mx [Centro de Investigación en Ciencias, IICBA, Universidad Autónoma del Estado de Morelos, Av. Universidad 1001, Col. Chamilpa, 62209 Cuernavaca, Morelos, México (Mexico); Unidad Académica de Física, Universidad Autónoma de Zacatecas, Calzada Solidaridad Esquina Con Paseo La Bufa S/N, 98060 Zacatecas, Zac., México (Mexico)

    2016-03-15

    Graphene Superlattices (GSs) have attracted a lot of attention due to its peculiar properties as well as its possible technological implications. Among these characteristics we can mention: the extra Dirac points in the dispersion relation and the highly anisotropic propagation of the charge carriers. However, despite the intense research that is carried out in GSs, so far there is no report about the angular dependence of the Transmission Gap (TG) in GSs. Here, we report the dependence of TG as a function of the angle of the incident Dirac electrons in a rather simple Electrostatic GS (EGS). Our results show that the angular dependence of the TG is intricate, since for moderated angles the dependence is parabolic, while for large angles an exponential dependence is registered. We also find that the TG can be modulated from meV to eV, by changing the structural parameters of the GS. These characteristics open the possibility for an angle-dependent bandgap engineering in graphene.

  5. High-Temperature, Wirebondless, Ultracompact Wide Bandgap Power Semiconductor Modules

    Science.gov (United States)

    Elmes, John

    2015-01-01

    Silicon carbide (SiC) and other wide bandgap semiconductors offer great promise of high power rating, high operating temperature, simple thermal management, and ultrahigh power density for both space and commercial power electronic systems. However, this great potential is seriously limited by the lack of reliable high-temperature device packaging technology. This Phase II project developed an ultracompact hybrid power module packaging technology based on the use of double lead frames and direct lead frame-to-chip transient liquid phase (TLP) bonding that allows device operation up to 450 degC. The new power module will have a very small form factor with 3-5X reduction in size and weight from the prior art, and it will be capable of operating from 450 degC to -125 degC. This technology will have a profound impact on power electronics and energy conversion technologies and help to conserve energy and the environment as well as reduce the nation's dependence on fossil fuels.

  6. Negative voltage bandgap reference with multilevel curvature compensation technique

    Science.gov (United States)

    Xi, Liu; Qian, Liu; Xiaoshi, Jin; Yongrui, Zhao; Lee, Jong-Ho

    2016-05-01

    A novel high-order curvature compensation negative voltage bandgap reference (NBGR) based on a novel multilevel compensation technique is introduced. Employing an exponential curvature compensation (ECC) term with many high order terms in itself, in a lower temperature range (TR) and a multilevel curvature compensation (MLCC) term in a higher TR, a flattened and better effect of curvature compensation over the TR of 165 °C (-40 to 125 °C) is realised. The MLCC circuit adds two convex curves by using two sub-threshold operated NMOS. The proposed NBGR implemented in the Central Semiconductor Manufacturing Corporation (CSMC) 0.5 μm BCD technology demonstrates an accurate voltage of -1.183 V with a temperature coefficient (TC) as low as 2.45 ppm/°C over the TR of 165 °C at a -5.0 V power supply; the line regulation is 3 mV/V from a -5 to -2 V supply voltage. The active area of the presented NBGR is 370 × 180 μm2. Project supported by the Fund of Liaoning Province Education Department (No. L2013045).

  7. Morphology effects on the bandgap of silicon nanocrystals—Numerically modelled by a full multi-grid method

    Science.gov (United States)

    Puthen Veettil, Binesh; König, Dirk; Huang, Shujuan; Patterson, Robert; Conibeer, Gavin

    2017-02-01

    Silicon nanocrystals embedded in a dielectric matrix have been considered a potential candidate for many optoelectronic and photovoltaic applications and have been under vigorous study in recent years. One of the main properties of interest in this application is the absorption bandgap, which is determined by the quantum confinement of silicon nanocrystals. The ability to predict the absorption bandgap is a key step in designing an optimum solar cell using this material. Although several higher level algorithms are available to predict the electronic confinement in these nanocrystals, most of them make regular-shape assumptions for the ease of computation. In this work, we present a model for the accurate prediction of the quantum confinement in silicon nanocrystals of non-regular shape by employing an efficient, self-consistent Full-Multi-Grid method. Confined energies in spherical, elongated, and arbitrarily shaped nanocrystals are calculated. The excited level calculations quantify the wavefunction coupling and energy level splitting arising due to the proximity of dots. The splitting magnitude was found to be as high as 0.1 eV for the 2 nm size silicon quantum dots. The decrease in confinement energy due to the elongation of dots was found to be more than 0.2 eV, and the trend was similar for different dielectric materials. Theoretical predictions were compared to the results from optical and structural characterisation and found to be in agreement. The loss of degeneracy in highly asymmetric quantum dots, such as a "horse-shoe" shaped quantum dot, significantly affects the excited state energies.

  8. Photonic bandgap fiber lasers and multicore fiber lasers for next generation high power lasers

    DEFF Research Database (Denmark)

    Shirakawa, A.; Chen, M.; Suzuki, Y.

    2014-01-01

    Photonic bandgap fiber lasers are realizing new laser spectra and nonlinearity mitigation that a conventional fiber laser cannot. Multicore fiber lasers are a promising tool for power scaling by coherent beam combination. © 2014 OSA.......Photonic bandgap fiber lasers are realizing new laser spectra and nonlinearity mitigation that a conventional fiber laser cannot. Multicore fiber lasers are a promising tool for power scaling by coherent beam combination. © 2014 OSA....

  9. 167 W, 1178 nm Ytterbium-Doped Photonic Bandgap Fiber Amplifier with Power Scalability

    DEFF Research Database (Denmark)

    Olausson, Christina Bjarnal Thulin; Shirakawa, Akira; Chen, Meishin

    2010-01-01

    We have generated 167 W of output power at 1178 nm using an ytterbium-doped photonic bandgap fiber. Distributed spectral filtering efficiently suppresses amplified spontaneous emission at shorter wavelengths and enables power scalable amplification at 1178nm.......We have generated 167 W of output power at 1178 nm using an ytterbium-doped photonic bandgap fiber. Distributed spectral filtering efficiently suppresses amplified spontaneous emission at shorter wavelengths and enables power scalable amplification at 1178nm....

  10. Properties of photonic bandgap in one-dimensional multicomponent photonic crystal

    Institute of Scientific and Technical Information of China (English)

    ZHANG Yi; WANG Qi

    2006-01-01

    Properties of photonic band gap and light propagation in one-dimensional multicomponent photonic crystal have been studied with the optical transfer matrix method.We mainly analyze the relation of photonic band-gap property with the arrangement of components,the refractive index and the geometrical thickness.In this study,the methods to change the width and the location of the existing photonic band-gaps in multicomponent photonic crystal are proposed.

  11. Power-scalable long-wavelength Yb-doped photonic bandgap fiber sources

    DEFF Research Database (Denmark)

    Olausson, Christina Bjarnal Thulin; Shirakawa, Akira; Maurayama, Hiroki

    2010-01-01

    Ytterbium-doped photonic-bandgap fiber sources operationg at the long-wavelength edge of the ytterbium gain band are being investigated for high power amplification. Artificial shaping of the gain spectrum by the characteristic distributed filtering effect of the photonic bandgap enables...... spontaneous-emission-free power svaling. As high as 167 W power and 16 dB saturated gain at 1178 nm have been demonstrated...

  12. Modeling of Z-scan characteristics for one-dimensional nonlinear photonic bandgap materials.

    Science.gov (United States)

    Chen, Shuqi; Zang, Weiping; Schülzgen, Axel; Liu, Xin; Tian, Jianguo; Moloney, Jerome V; Peyghambarian, Nasser

    2009-12-01

    We propose a Z-scan theory for one-dimensional nonlinear photonic bandgap materials. The Z-scan characteristics for this material are analyzed. Results show that the Z-scan curves for photonic bandgap materials with nonlinear refraction are similar to those of uniform materials exhibiting both nonlinear refraction and nonlinear absorption simultaneously. Effects of nonlinear absorption on reflected and transmitted Z-scan results are also discussed.

  13. Electrially tunable photonic bandgap guidance in a liquid crystal filled photonic crystal fiber

    DEFF Research Database (Denmark)

    Haakestad, Magnus W.; Alkeskjold, Thomas Tanggaard; Nielsen, Martin Dybendal;

    2005-01-01

    Tunable bandgap guidance is obtained by filling the holes of a solid core photonic crystal fiber with a nematic liquid crystal and applying an electric field. The response times are measured and found to be in the millisecond range.......Tunable bandgap guidance is obtained by filling the holes of a solid core photonic crystal fiber with a nematic liquid crystal and applying an electric field. The response times are measured and found to be in the millisecond range....

  14. Thin-Film Solar Cells on Polymer Substrates for Space Power

    Science.gov (United States)

    Hepps, A. F.; McNatt, Jeremiah; Morel, D. L.; Ferckides, C. S.; Jin, M. H.; Orbey, N.; Cushman, M.; Birkmire, R. W.; Shafarman, W. N.; Newton, R.

    2004-01-01

    Photovoltaic arrays have played a key role in power generation in space. The current technology will continue to evolve but is limited in the important mass specific power metric (MSP or power/weight ratio) because it is based on bulk crystal technology. Solar cells based on thin-film materials offer the promise of much higher MSP and much lower cost. However, for many space applications, a 20% or greater AM0 efficiency (eta) may be required. The leading thin-film materials, amorphous Si, CuInSe, and CdTe have seen significant advances in efficiency over the last decade but will not achieve the required efficiency in the near future. Several new technologies are herein described to maximize both device eta and MSP. We will discuss these technologies in the context of space exploration and commercialization. One novel approach involves the use of very lightweight polyimide substrates. We describe efforts to enable this advance including materials processing and device fabrication and characterization. Another approach involves stacking two cells on top of each other. These tandem devices more effectively utilize solar radiation by passing through non-absorbed longer wavelength light to a narrow-bandgap bottom cell material. Modeling of current devices in tandem format indicates that AM0 efficiencies near 20% can be achieved with potential for 25% in the near future. Several important technical issues need to be resolved to realize the benefits of lightweight technologies for solar arrays, such as: monolithic interconnects, lightweight array structures, and new ultra-light support and deployment mechanisms. Recent advances will be stressed.

  15. Solar pond

    Science.gov (United States)

    Miller, C. G.; Stephens, J. B. (Inventor)

    1978-01-01

    Shallow pools of liquid to collect low-temperature solar generated thermal energy are described. Narrow elongated trenches, grouped together over a wide area, are lined with a heat-absorbing black liner. The heat-absorbing liquid is kept separate from the thermal energy removing fluid by means such as clear polyethylene material. The covering for the pond may be a fluid or solid. If the covering is a fluid, fire fighting foam, continuously generated, or siloons are used to keep the surface covering clean and insulated. If the thermal energy removing fluid is a gas, a fluid insulation layer contained in a flat polyethlene tubing is used to cover the pond. The side of the tube directed towards the sun is treated to block out ultraviolet radiation and trap in infrared radiation.

  16. Optical bandgap of single- and multi-layered amorphous germanium ultra-thin films

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Pei; Zaslavsky, Alexander [Department of Physics and School of Engineering, Brown University, 182-184 Hope St., Providence, Rhode Island 02912 (United States); Longo, Paolo [Gatan, Inc., 5794 W Las Positas Blvd., Pleasanton, California 94588 (United States); Pacifici, Domenico, E-mail: Domenico-Pacifici@brown.edu [School of Engineering, Brown University, 184 Hope St., Providence, Rhode Island 02912 (United States)

    2016-01-07

    Accurate optical methods are required to determine the energy bandgap of amorphous semiconductors and elucidate the role of quantum confinement in nanometer-scale, ultra-thin absorbing layers. Here, we provide a critical comparison between well-established methods that are generally employed to determine the optical bandgap of thin-film amorphous semiconductors, starting from normal-incidence reflectance and transmittance measurements. First, we demonstrate that a more accurate estimate of the optical bandgap can be achieved by using a multiple-reflection interference model. We show that this model generates more reliable results compared to the widely accepted single-pass absorption method. Second, we compare two most representative methods (Tauc and Cody plots) that are extensively used to determine the optical bandgap of thin-film amorphous semiconductors starting from the extracted absorption coefficient. Analysis of the experimental absorption data acquired for ultra-thin amorphous germanium (a-Ge) layers demonstrates that the Cody model is able to provide a less ambiguous energy bandgap value. Finally, we apply our proposed method to experimentally determine the optical bandgap of a-Ge/SiO{sub 2} superlattices with single and multiple a-Ge layers down to 2 nm thickness.

  17. Optical bandgap of single- and multi-layered amorphous germanium ultra-thin films

    Science.gov (United States)

    Liu, Pei; Longo, Paolo; Zaslavsky, Alexander; Pacifici, Domenico

    2016-01-01

    Accurate optical methods are required to determine the energy bandgap of amorphous semiconductors and elucidate the role of quantum confinement in nanometer-scale, ultra-thin absorbing layers. Here, we provide a critical comparison between well-established methods that are generally employed to determine the optical bandgap of thin-film amorphous semiconductors, starting from normal-incidence reflectance and transmittance measurements. First, we demonstrate that a more accurate estimate of the optical bandgap can be achieved by using a multiple-reflection interference model. We show that this model generates more reliable results compared to the widely accepted single-pass absorption method. Second, we compare two most representative methods (Tauc and Cody plots) that are extensively used to determine the optical bandgap of thin-film amorphous semiconductors starting from the extracted absorption coefficient. Analysis of the experimental absorption data acquired for ultra-thin amorphous germanium (a-Ge) layers demonstrates that the Cody model is able to provide a less ambiguous energy bandgap value. Finally, we apply our proposed method to experimentally determine the optical bandgap of a-Ge/SiO2 superlattices with single and multiple a-Ge layers down to 2 nm thickness.

  18. Modulation of bandgap in bilayer armchair graphene ribbons by tuning vertical and transverse electric fields

    Science.gov (United States)

    Vu, Thanh-Tra; Nguyen, Thi-Kim-Quyen; Huynh, Anh-Huy; Phan, Thi-Kim-Loan; Tran, Van-Truong

    2017-02-01

    We investigate the effects of external electric fields on the electronic properties of bilayer armchair graphene nano-ribbons. Using atomistic simulations with Tight Binding calculations and the Non-equilibrium Green's function formalism, we demonstrate that (i) in semi-metallic structures, vertical fields impact more effectively than transverse fields in terms of opening larger bandgap, showing a contrary phenomenon compared to that demonstrated in previous studies in bilayer zigzag graphene nano-ribbons; (ii) in some semiconducting structures, if transverse fields just show usual effects as in single layer armchair graphene nano-ribbons where the bandgap is suppressed when varying the applied potential, vertical fields exhibit an anomalous phenomenon that the bandgap can be enlarged, i.e., for a structure of width of 16 dimer lines, the bandgap increases from 0.255 eV to the maximum value of 0.40 eV when a vertical bias equates 0.96 V applied. Although the combined effect of two fields does not enlarge the bandgap as found in bilayer zigzag graphene nano-ribbons, it shows that the mutual effect can be useful to reduce faster the bandgap in semiconducting bilayer armchair graphene nano-ribbons. These results are important to fully understand the effects of electric fields on bilayer graphene nano-ribbons (AB stacking) and also suggest appropriate uses of electric gates with different edge orientations.

  19. Bandgaps and directional properties of two-dimensional square beam-like zigzag lattices

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Yan-Feng; Wang, Yue-Sheng, E-mail: yswang@bjtu.edu.cn [Institute of Engineering Mechanics, Beijing Jiaotong University, Beijing 100044 (China); Zhang, Chuanzeng [Department of Civil Engineering, University of Siegen, Siegen 57068 (Germany)

    2014-12-15

    In this paper we propose four kinds of two-dimensional square beam-like zigzag lattice structures and study their bandgaps and directional propagation of elastic waves. The band structures are calculated by using the finite element method. Both the in-plane and out-of-plane waves are investigated simultaneously via the three-dimensional Euler beam elements. The mechanism of the bandgap generation is analyzed by studying the vibration modes at the bandgap edges. The effects of the geometry parameters of the xy- and z-zigzag lattices on the bandgaps are investigated and discussed. Multiple complete bandgaps are found owing to the separation of the degeneracy by introducing bending arms. The bandgaps are sensitive to the geometry parameters of the periodic systems. The deformed displacement fields of the harmonic responses of a finite lattice structure subjected to harmonic loads at different positions are illustrated to show the directional wave propagation. An extension of the proposed concept to the hexagonal lattices is also presented. The research work in this paper is relevant to the practical design of cellular structures with enhanced vibro-acoustics performance.

  20. Microlayer during boiling in narrow slot channels

    Science.gov (United States)

    Diev, Mikhail D.; Leontiev, Alexander I.

    1997-01-01

    An international space station Alpha will have a two-phase thermal control system. Boiling of a liquid ammonia will be a process of heat collection in evaporative heat exchangers. Unfortunately, only little data is available for boiling heat transfer in microgravity. Geometries of boiling channels working good in normal gravity are not appropriate in microgravity, and special means should be worked out to avoid some undesired events. From this point of view, the narrow slot channels may be assumed as a promising geometry for microgravity operation. During boiling in narrow slots, the vapor bubbles are flattened between the channel walls. The vapor phase and the channel wall are separated by a thin liquid film which is known as a microlayer. The paper presents the experimental results compared to the theoretical analysis, the paper also shows the narrow slot channels as a perspective configuration for microgravity applications.

  1. Synthesis of iron oxide nanoparticles of narrow size distribution on polysaccharide templates

    Indian Academy of Sciences (India)

    M Nidhin; R Indumathy; K J Sreeram; Balachandran Unni Nair

    2008-02-01

    We report here the preparation of nanoparticles of iron oxide in the presence of polysaccharide templates. Interaction between iron (II) sulfate and template has been carried out in aqueous phase, followed by the selective and controlled removal of the template to achieve narrow distribution of particle size. Particles of iron oxide obtained have been characterized for their stability in solvent media, size, size distribution and crystallinity and found that when the negative value of the zeta potential increases, particle size decreases. A narrow particle size distribution with 100 = 275 nm was obtained with chitosan and starch templates. SEM measurements further confirm the particle size measurement. Diffuse reflectance UV–vis spectra values show that the template is completely removed from the final iron oxide particles and powder XRD measurements show that the peaks of the diffractogram are in agreement with the theoretical data of hematite. The salient observations of our study shows that there occurs a direct correlation between zeta potential, polydispersity index, bandgap energy and particle size. The crystallite size of the particles was found to be 30–35 nm. A large negative zeta potential was found to be advantageous for achieving lower particle sizes, owing to the particles remaining discrete without agglomeration.

  2. Effects of corrugation shape on frequency band-gaps for longitudinal wave motion in a periodic elastic layer

    DEFF Research Database (Denmark)

    Sorokin, Vladislav

    2016-01-01

    The paper concerns determining frequency band-gaps for longitudinal wave motion in a periodic waveguide. The waveguide may be considered either as an elastic layer with variable thickness or as a rod with variable cross section. As a result, widths and locations of all frequency band-gaps are det......The paper concerns determining frequency band-gaps for longitudinal wave motion in a periodic waveguide. The waveguide may be considered either as an elastic layer with variable thickness or as a rod with variable cross section. As a result, widths and locations of all frequency band......-gaps are determined by means of the method of varying amplitudes. For the general symmetric corrugation shape, the width of each odd band-gap is controlled only by one harmonic in the corrugation series with its number being equal to the number of the band-gap. Widths of even band-gaps, however, are influenced by all...... the harmonics involved in the corrugation series, so that the lower frequency band-gaps can emerge. These are band-gaps located below the frequency corresponding to the lowest harmonic in the corrugation series. For the general non-symmetric corrugation shape, the mth band-gap is controlled only by one, the mth...

  3. Efficient, Narrow-Pass-Band Optical Filters

    Science.gov (United States)

    Sandford, Stephen P.

    1996-01-01

    Optical filters with both narrow pass bands and high efficiencies fabricated to design specifications. Offer tremendous improvements in performance for number of optical (including infrared) systems. In fiber-optic and free-space communication systems, precise frequency discrimination afforded by narrow pass bands of filters provide higher channel capacities. In active and passive remote sensors like lidar and gas-filter-correlation radiometers, increased efficiencies afforded by filters enhance detection of small signals against large background noise. In addition, sizes, weights, and power requirements of many optical and infrared systems reduced by taking advantage of gains in signal-to-noise ratios delivered by filters.

  4. On Narrow Nucleon Excitation N*(1685)

    CERN Document Server

    Kuznetsov, V; Thuermann, M

    2011-01-01

    We collected notes and simple estimates about putative narrow nucleon N*(1685) - the candidate for the non-strange member of the exotic anti-decuplet of baryons. In particular, we consider the recent high precision data on eta photoproduction off free proton obtained by the Crystal Ball Collaboration at MAMI. We show that it is difficult to describe peculiarities of these new data in the invariant energy interval of W ~ 1650-1750 MeV in terms of known wide resonances. Using very simple estimates, we show that the data may indicate an existence of a narrow N*(1685) with small photocoupling to the proton.

  5. Non-resonant wavelength modulation saturation spectroscopy in acetylene-filled hollow-core photonic bandgap fibres applied to modulation-free laser diode stabilisation.

    Science.gov (United States)

    Pineda-Vadillo, Pablo; Lynch, Michael; Charlton, Christy; Donegan, John F; Weldon, Vincent

    2009-12-07

    In this paper the application of Wavelength Modulation (WM) techniques to non-resonant saturation spectroscopy in acetylene-filled Hollow-Core Photonic Bandgap Fibres (HC-PBFs) and modulation-free Laser Diode (LD) frequency stabilisation is investigated. In the first part WM techniques are applied to non-resonant pump-probe saturation of acetylene overtone rotational transitions in a HC-PBF. A high-power DFB chip-on-carrier mounted LD is used in conjunction with a tuneable External Cavity Laser (ECL) and the main saturation parameters are characterized. In the second part a novel feedback system to stabilize the DFB emission wavelength based on the WM saturation results is implemented. Modulation-free locking of the DFB laser frequency to the narrow linewidth saturation feature is achieved for both constant and variable LD temperatures.

  6. Pressure-induced phase transition and bandgap collapse in the wide-bandgap semiconductor InTaO4

    CERN Document Server

    Errandonea, D; Garg, A B; Botella, P; Martinez-Garcia, D; Pellicer-Porres, J; Rodriguez-Hernandez, P; Munoz, A; Cuenca-Gotor, V; Sans, J A

    2016-01-01

    A pressure-induced phase transition, associated with an increase of the coordination number of In and Ta, is detected beyond 13 GPa in InTaO4 by combining synchrotron x-ray diffraction and Raman measurements in a diamond anvil cell with ab-initio calculations. High-pressure optical-absorption measurements were also carried out. The high-pressure phase has a monoclinic structure which shares the same space group with the low-pressure phase (P2/c). The structure of the high-pressure phase can be considered as a slight distortion of an orthorhombic structure described by space group Pcna. The phase transition occurs together with a unit-cell volume collapse and an electronic bandgap collapse observed by experiments and calculations. Additionally, a band crossing is found to occur in the low-pressure phase near 7 GPa. The pressure dependence of all the Raman-active modes is reported for both phases as well as the pressure dependence of unit-cell parameters and the equations of state. Calculations also provide inf...

  7. On electrode pinning and charge blocking layers in organic solar cells

    Science.gov (United States)

    Magen, Osnat; Tessler, Nir

    2017-05-01

    We use device modelling for studying the losses introduced by metallic electrodes in organic solar cells' device structure. We first discuss the inclusion of pinning at the integer charge transfer state in device models, with and without using the image charge potential. In the presence of disorder, the space charge introduced due to the image potential enhances the pinning by more than 0.2 eV. The explicit introduction of the image potential creates band-gap narrowing at the contact, thus affecting both dark leakage current and photo conversion efficiency. We find that there are two regimes in which the contacts may limit the performance. For low (moderate) barriers, the contacts introduce minority carrier recombination at the contacts that adds to the bulk recombination channels. Only for high barriers, the contacts directly limit the open circuit voltage and impose a value that is equal to the contact's energy difference. Examining the device structures with blocking layers, we find that these are mainly useful for the low to moderate contacts' barriers and that for the high barrier case, the enhancement of open circuit voltage may be accompanied by the introduction of serial resistance or S shape.

  8. Singlet Exciton Lifetimes in Conjugated Polymer Films for Organic Solar Cells

    KAUST Repository

    Dimitrov, Stoichko

    2016-01-13

    The lifetime of singlet excitons in conjugated polymer films is a key factor taken into account during organic solar cell device optimization. It determines the singlet exciton diffusion lengths in polymer films and has a direct impact on the photocurrent generation by organic solar cell devices. However, very little is known about the material properties controlling the lifetimes of singlet excitons, with most of our knowledge originating from studies of small organic molecules. Herein, we provide a brief summary of the nature of the excited states in conjugated polymer films and then present an analysis of the singlet exciton lifetimes of 16 semiconducting polymers. The exciton lifetimes of seven of the studied polymers were measured using ultrafast transient absorption spectroscopy and compared to the lifetimes of seven of the most common photoactive polymers found in the literature. A plot of the logarithm of the rate of exciton decay vs. the polymer optical bandgap reveals a medium correlation between lifetime and bandgap, thus suggesting that the Energy Gap Law may be valid for these systems. This therefore suggests that small bandgap polymers can suffer from short exciton lifetimes, which may limit their performance in organic solar cell devices. In addition, the impact of film crystallinity on the exciton lifetime was assessed for a small bandgap diketopyrrolopyrrole co-polymer. It is observed that the increase of polymer film crystallinity leads to reduction in exciton lifetime and optical bandgap again in agreement with the Energy Gap Law.

  9. Singlet Exciton Lifetimes in Conjugated Polymer Films for Organic Solar Cells

    Directory of Open Access Journals (Sweden)

    Stoichko D. Dimitrov

    2016-01-01

    Full Text Available The lifetime of singlet excitons in conjugated polymer films is a key factor taken into account during organic solar cell device optimization. It determines the singlet exciton diffusion lengths in polymer films and has a direct impact on the photocurrent generation by organic solar cell devices. However, very little is known about the material properties controlling the lifetimes of singlet excitons, with most of our knowledge originating from studies of small organic molecules. Herein, we provide a brief summary of the nature of the excited states in conjugated polymer films and then present an analysis of the singlet exciton lifetimes of 16 semiconducting polymers. The exciton lifetimes of seven of the studied polymers were measured using ultrafast transient absorption spectroscopy and compared to the lifetimes of seven of the most common photoactive polymers found in the literature. A plot of the logarithm of the rate of exciton decay vs. the polymer optical bandgap reveals a medium correlation between lifetime and bandgap, thus suggesting that the Energy Gap Law may be valid for these systems. This therefore suggests that small bandgap polymers can suffer from short exciton lifetimes, which may limit their performance in organic solar cell devices. In addition, the impact of film crystallinity on the exciton lifetime was assessed for a small bandgap diketopyrrolopyrrole co-polymer. It is observed that the increase of polymer film crystallinity leads to reduction in exciton lifetime and optical bandgap again in agreement with the Energy Gap Law.

  10. Bandgap properties in locally resonant phononic crystal double panel structures with periodically attached spring-mass resonators

    Science.gov (United States)

    Qian, Denghui; Shi, Zhiyu

    2016-10-01

    Bandgap properties of the locally resonant phononic crystal double panel structure made of a two-dimensional periodic array of a spring-mass resonator surrounded by n springs (n equals to zero at the beginning of the study) connected between the upper and lower plates are investigated in this paper. The finite element method is applied to calculate the band structure, of which the accuracy is confirmed in comparison with the one calculated by the extended plane wave expansion (PWE) method and the transmission spectrum. Numerical results and further analysis demonstrate that two bands corresponding to the antisymmetric vibration mode open a wide band gap but is cut narrower by a band corresponding to the symmetric mode. One of the regulation rules shows that the lowest frequency on the symmetric mode band is proportional to the spring stiffness. Then, a new design idea of adding springs around the resonator in a unit cell (n is not equal to zero now) is proposed in the need of widening the bandwidth and lowering the starting frequency. Results show that the bandwidth of the band gap increases from 50 Hz to nearly 200 Hz. By introducing the quality factor, the regulation rules with the comprehensive consideration of the whole structure quality limitation, the wide band gap and the low starting frequency are also discussed.

  11. Bandgaps of the Chalcogenide Glass Hollow-Core Photonic Crystal Fiber

    Institute of Scientific and Technical Information of China (English)

    LI Shu-Guang; ZHOU Hong-Song; YIN Guo-Bing

    2011-01-01

    Bandgaps of chalcogenide glass hollow-core photonic crystal fibers (GLS HC-PCFs) are analyzed by using the plane-wave expansion method. A mid-infrared laser can propagate in these low confinement loss fibers when the wavelength falls into the bandgaps. For enlarging the bandgap width, an improved GLS HC-PCF is put forward, the normalized frequency kA of the improved fiber is from 7.2 to 8.5 in its first bandgap. The improved GLS HC-PCF with pitch of 4.2μm can transmit the lights with wavelengths ranging from 3.1μm to 3.7μm.%Bandgaps of chalcogenide glass hollow-core photonic crystal fibers (GLS HC-PCFs) are analyzed by using the plane-wave expansion method.A mid-infrared laser can propagate in these low confinement loss fibers when the wavelength falls into the bandgaps.For enlarging the bandgap width,an improved GLS HC-PCF is put forward,the normalized frequency κA of the improved fiber is from 7.2 to 8.5 in its first bandgap.The improved GLS HC-PCF with pitch of 4.2μm can transmit the lights with wavelengths ranging from 3.1 μm to 3.7 μm.Photonic crystal fibers (PCFs) can be classified into total internal reflection PCFs and photonic bandgap (PBG) PCFs[1] Solid core PCFs are one kind of the total internal reflection PCFs;hollow-core PCFs (HC-PCFs) are a kind of typical PBG fibers.The conception of HC-PCFs was first proposed by Russel in 1991.[2] Later,it was theoretically demonstrated by Birks et al.[3] in 1995.A bandgap photonic crystal fiber was mde by Knight et al.[4] for the first time in 1998.On the basis of these works,the first HC-PCF was designed and made by Cregan et al.[5] in 1999.

  12. A review of Air Force high efficiency cascaded multiple bandgap solar cell research and development

    Science.gov (United States)

    Rahilly, W. P.

    1979-01-01

    At the time of their conception, the cell stack systems to be discussed represent the best semiconductor materials combinations to achieve Air Force program goals. These systems are investigated thoroughly and the most promising systems, from the standpoint of high efficiency, are taken for further development with large area emphasized (at least 4 sq cm). The emphasis in the Air Force cascaded cell program is placed on eventual nonconcentrator application. This use of the final cell design considerably relieves the low resistance requirements for the tunnel junction. In a high concentration application the voltage drop across the tunnel junction can be a very serious problem.

  13. Highly Crystalline and Low Bandgap Donor Polymers for Efficient Polymer Solar Cells

    Science.gov (United States)

    2012-01-01

    298 (Rev. 8-98) Prescribed by ANSI Std Z39-18 539 www.advmat.de www.MaterialsViews.com C O M M U N IC A TIO N wileyonlinelibrary.com© 2012 WILEY-VCH...on the π–π packing of the main chains in EI-PFDTBT, as confirmed by X-ray diffraction ( XRD ) and UV/Vis absorption spectroscopic measurements...Figure 2a reproduces the XRD profile for a EI-PFDTBT powder. The strong diffraction peak at 21.3° indicates the 4.1 Å π-stacking spacing between polymer

  14. Three-terminal heterojunction bipolar transistor solar cell for high-efficiency photovoltaic conversion.

    Science.gov (United States)

    Martí, A; Luque, A

    2015-04-22

    Here we propose, for the first time, a solar cell characterized by a semiconductor transistor structure (n/p/n or p/n/p) where the base-emitter junction is made of a high-bandgap semiconductor and the collector is made of a low-bandgap semiconductor. We calculate its detailed-balance efficiency limit and prove that it is the same one than that of a double-junction solar cell. The practical importance of this result relies on the simplicity of the structure that reduces the number of layers that are required to match the limiting efficiency of dual-junction solar cells without using tunnel junctions. The device naturally emerges as a three-terminal solar cell and can also be used as building block of multijunction solar cells with an increased number of junctions.

  15. Narrow-Band Applications of Communications Satellites.

    Science.gov (United States)

    Cowlan, Bert; Horowitz, Andrew

    This paper attempts to describe the advantages of "narrow-band" applications of communications satellites for education. It begins by discussing the general controversy surrounding the use of satellites in education, by placing the concern within the larger context of the general debate over the uses of new technologies in education, and by…

  16. Narrow vision after view-broadening travel.

    Science.gov (United States)

    Melo, Mariana de Mendonça; Ciriano, Jose P Martinez; van Genderen, Perry J J

    2008-01-01

    Loss of vision is a threatening presentation of disease. We describe a case of acute idiopathic blind spot enlargement in a 26-year-old male traveler who presented with narrow vision after a journey to Indonesia. Although the patient used mefloquine at time of presentation, we were unable to retrieve sound data incriminating mefloquine in this rare eye disorder.

  17. Solar neutrino oscillation phenomenology

    Indian Academy of Sciences (India)

    Srubabati Goswami

    2004-02-01

    This article summarises the status of the solar neutrino oscillation phenomenology at the end of 2002 in the light of the SNO and KamLAND results. We first present the allowed areas obtained from global solar analysis and demonstrate the preference of the solar data towards the large-mixing-angle (LMA) MSW solution. A clear confirmation in favour of the LMA solution comes from the KamLAND reactor neutrino data. the KamLAND spectral data in conjunction with the global solar data further narrows down the allowed LMA region and splits it into two allowed zones - a low $ m^{2}$ region (low-LMA) and high $ m^{2}$ region (high-LMA). We demonstrate through a projected analysis that with an exposure of 3 kton-year (kTy) KamLAND can remove this ambiguity.

  18. Triblock-Terpolymer-Directed Self-Assembly of Mesoporous TiO2: High-Performance Photoanodes for Solid-State Dye-Sensitized Solar Cells

    KAUST Repository

    Docampo, Pablo

    2012-04-30

    A new self-assembly platform for the fast and straightforward synthesis of bicontinuous, mesoporous TiO 2 films is presented, based on the triblock terpolymer poly(isoprene - b - styrene - b - ethylene oxide). This new materials route allows the co-assembly of the metal oxide as a fully interconnected minority phase, which results in a highly porous photoanode with strong advantages over the state-of-the-art nanoparticle-based photoanodes employed in solidstate dye-sensitized solar cells. Devices fabricated through this triblock terpolymer route exhibit a high availability of sub-bandgap states distributed in a narrow and low enough energy band, which maximizes photoinduced charge generation from a state-of-the-art organic dye, C220. As a consequence, the co-assembled mesoporous metal oxide system outperformed the conventional nanoparticle-based electrodes fabricated and tested under the same conditions, exhibiting solar power-conversion efficiencies of over 5%. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  19. Investigation of defect luminescence from multicrystalline Si wafer solar cells using X-ray fluorescence and luminescence imaging

    Energy Technology Data Exchange (ETDEWEB)

    Peloso, Matthew P. [Department of Electrical and Computer Engineering, National University of Singapore (Singapore); Palina, Natalie; Hidayat, Hidayat; Hoex, Bram [Solar Energy Research Institute of Singapore (SERIS), National University of Singapore (Singapore); Banas, Krzysztof; Banas, Agnieszka; Breese, Mark B.H. [Singapore Synchrotron Light Source, National University of Singapore (Singapore); Aberle, Armin G. [Department of Electrical and Computer Engineering, National University of Singapore (Singapore); Solar Energy Research Institute of Singapore (SERIS), National University of Singapore (Singapore)

    2012-12-15

    Multicrystalline silicon wafer solar cells reveal performance- reducing defects by luminescence. X-ray fluorescence spectra are used to investigate the elemental constituents from regions of solar cells yielding reverse-bias or sub-bandgap luminescence from defects. It is found that a higher concentration of metals is present in regions yielding reverse-bias electroluminescence than in regions yielding sub-bandgap electroluminescence. This suggests, dislocations do not create strong breakdown currents in the absence of impurity precipitates. (a) Topographies of sub-bandgap (red) and reverse-bias (blue) luminescence from defects in a multicrystalline Si wafer solar cell. (b) Their distinct X-ray spectra indicate highest concentrations of metals in the blue regions. (copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  20. Quantum-Tuned Multijunction Solar Cells

    Science.gov (United States)

    Koleilat, Ghada I.

    Multijunction solar cells made from a combination of CQDs of differing sizes and thus bandgaps are a promising means by which to increase the energy harvested from the Sun's broad spectrum. In this dissertation, we first report the systematic engineering of 1.6 eV PbS CQD solar cells, optimal as the front cell responsible for visible wavelength harvesting in tandem photovoltaics. We rationally optimize each of the device's collecting electrodes---the heterointerface with electron accepting TiO2 and the deep-work-function hole-collecting MoO3 for ohmic contact---for maximum efficiency. Room-temperature processing enables flexible substrates, and permits tandem solar cells that integrate a small-bandgap back cell atop a low thermal-budget larger-bandgap front cell. We report an electrode strategy that enables a depleted heterojunction CQD PV device to be fabricated entirely at room temperature. We develop a two-layer donor-supply electrode (DSE) in which a highly doped, shallow work function layer supplies a high density of free electrons to an ultrathin TiO2 layer via charge-transfer doping. Using the DSE we build all-room-temperature-processed small-bandgap (1 eV) colloidal quantum dot solar cells suitable for use as the back junction in tandem solar cells. We further report in this work the first efficient CQD tandem solar cells. We use a graded recombination layer (GRL) to provide a progression of work functions from the hole-accepting electrode in the bottom cell to the electron-accepting electrode in the top cell. The recombination layers must allow the hole current from one cell to recombine, with high efficiency and low voltage loss, with the electron current from the next cell. We conclude our dissertation by presenting the generalized conditions for design of efficient graded recombination layer solar devices. We demonstrate a family of new GRL designs experimentally and highlight the benefits of the progression of dopings and work functions in the

  1. Single-step colloidal quantum dot films for infrared solar harvesting

    KAUST Repository

    Kiani, Amirreza

    2016-11-01

    Semiconductors with bandgaps in the near- to mid-infrared can harvest solar light that is otherwise wasted by conventional single-junction solar cell architectures. In particular, colloidal quantum dots (CQDs) are promising materials since they are cost-effective, processed from solution, and have a bandgap that can be tuned into the infrared (IR) via the quantum size effect. These characteristics enable them to harvest the infrared portion of the solar spectrum to which silicon is transparent. To date, IR CQD solar cells have been made using a wasteful and complex sequential layer-by-layer process. Here, we demonstrate ∼1 eV bandgap solar-harvesting CQD films deposited in a single step. By engineering a fast-drying solvent mixture for metal iodide-capped CQDs, we deposited active layers greater than 200 nm in thickness having a mean roughness less than 1 nm. We integrated these films into infrared solar cells that are stable in air and exhibit power conversion efficiencies of 3.5% under illumination by the full solar spectrum, and 0.4% through a simulated silicon solar cell filter.

  2. Single-step colloidal quantum dot films for infrared solar harvesting

    Science.gov (United States)

    Kiani, Amirreza; Sutherland, Brandon R.; Kim, Younghoon; Ouellette, Olivier; Levina, Larissa; Walters, Grant; Dinh, Cao-Thang; Liu, Mengxia; Voznyy, Oleksandr; Lan, Xinzheng; Labelle, Andre J.; Ip, Alexander H.; Proppe, Andrew; Ahmed, Ghada H.; Mohammed, Omar F.; Hoogland, Sjoerd; Sargent, Edward H.

    2016-10-01

    Semiconductors with bandgaps in the near- to mid-infrared can harvest solar light that is otherwise wasted by conventional single-junction solar cell architectures. In particular, colloidal quantum dots (CQDs) are promising materials since they are cost-effective, processed from solution, and have a bandgap that can be tuned into the infrared (IR) via the quantum size effect. These characteristics enable them to harvest the infrared portion of the solar spectrum to which silicon is transparent. To date, IR CQD solar cells have been made using a wasteful and complex sequential layer-by-layer process. Here, we demonstrate ˜1 eV bandgap solar-harvesting CQD films deposited in a single step. By engineering a fast-drying solvent mixture for metal iodide-capped CQDs, we deposited active layers greater than 200 nm in thickness having a mean roughness less than 1 nm. We integrated these films into infrared solar cells that are stable in air and exhibit power conversion efficiencies of 3.5% under illumination by the full solar spectrum, and 0.4% through a simulated silicon solar cell filter.

  3. Tuning Bandgap of p-Type Cu2Zn(Sn, Ge)(S, Se)4 Semiconductor Thin Films via Aqueous Polymer-Assisted Deposition.

    Science.gov (United States)

    Yi, Qinghua; Wu, Jiang; Zhao, Jie; Wang, Hao; Hu, Jiapeng; Dai, Xiao; Zou, Guifu

    2017-01-18

    Bandgap engineering of kesterite Cu2Zn(Sn, Ge)(S, Se)4 with well-controlled stoichiometric composition plays a critical role in sustainable inorganic photovoltaics. Herein, a cost-effective and reproducible aqueous solution-based polymer-assisted deposition approach is developed to grow p-type Cu2Zn(Sn, Ge)(S, Se)4 thin films with tunable bandgap. The bandgap of Cu2Zn(Sn, Ge)(S, Se)4 thin films can be tuned within the range 1.05-1.95 eV using the aqueous polymer-assisted deposition by accurately controlling the elemental compositions. One of the as-grown Cu2Zn(Sn, Ge)(S, Se)4 thin films exhibits a hall coefficient of +137 cm(3)/C. The resistivity, concentration and carrier mobility of the Cu2ZnSn(S, Se)4 thin film are 3.17 ohm·cm, 4.5 × 10(16) cm(-3), and 43 cm(2)/(V·S) at room temperature, respectively. Moreover, the Cu2ZnSn(S, Se)4 thin film when used as an active layer in a solar cell leads to a power conversion efficiency of 3.55%. The facile growth of Cu2Zn(Sn, Ge)(S, Se)4 thin films in an aqueous system, instead of organic solvents, provides great promise as an environmental-friendly platform to fabricate a variety of single/multi metal chalcogenides for the thin film industry and solution-processed photovoltaic devices.

  4. New Vacuum Solar Telescope

    Institute of Scientific and Technical Information of China (English)

    2011-01-01

    With its pure aperture up to 985mm, the New Vacuum Solar Telescope of China (NVST) has become the world's biggest vacuum solar telescope. The main science task of NVST is the high-resolution observation of photosphere and chromosphere including their fine structure of magnetic field on the sun. The NVST was equipped with many new technologies and powerful instruments, such as an adaptive optical system, a polarization analyzer, two vertical spectrographs, a high-resolution image system and a very narrow Ha filter (0.125A).

  5. Solar Indices - Solar Corona

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Collection includes a variety of indices related to solar activity contributed by a number of national and private solar observatories located worldwide. This...

  6. Solar Indices - Solar Flares

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Collection includes a variety of indices related to solar activity contributed by a number of national and private solar observatories located worldwide. This...

  7. Solar Indices - Solar Irradiance

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Collection includes a variety of indices related to solar activity contributed by a number of national and private solar observatories located worldwide. This...

  8. Solar Indices - Solar Ultraviolet

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Collection includes a variety of indices related to solar activity contributed by a number of national and private solar observatories located worldwide. This...

  9. Characterization and improved solar light activity of vanadium doped TiO{sub 2}/diatomite hybrid catalysts

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Bin, E-mail: b.wang6@uq.edu.au [School of Chemical and Environmental Engineering, China University of Mining & Technology, Beijing 100083 (China); School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Qld 4072 (Australia); Zhang, Guangxin, E-mail: z111@163.com [School of Chemical and Environmental Engineering, China University of Mining & Technology, Beijing 100083 (China); Leng, Xue, E-mail: xue.leng@uq.net.au [School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Qld 4072 (Australia); Sun, Zhiming, E-mail: zhiming.baxia@163.com [School of Chemical and Environmental Engineering, China University of Mining & Technology, Beijing 100083 (China); Zheng, Shuilin, E-mail: shuilinzheng8@gmail.com [School of Chemical and Environmental Engineering, China University of Mining & Technology, Beijing 100083 (China)

    2015-03-21

    Highlights: • V-doped TiO{sub 2}/diatomite composite photocatalyst was synthesized. • The physiochemical property and solar light photoactivity were characterized. • The presence and influence of V ions in TiO{sub 2} matrix was systematically analyzed. • The photocatalysis for Rhodamine B were studied under solar light illumination. - Abstract: V-doped TiO{sub 2}/diatomite composite photocatalysts with different vanadium concentrations were synthesized by a modified sol–gel method. The diatomite was responsible for the well dispersion of TiO{sub 2} nanoparticles on the matrix and consequently inhibited the agglomeration. V-TiO{sub 2}/diatomite hybrids showed red shift in TiO{sub 2} absorption edge with enhanced absorption intensity. Most importantly, the dopant energy levels were formed in the TiO{sub 2} bandgap due to V{sup 4+} ions substituted to Ti{sup 4+} sites. The 0.5% V-TiO{sub 2}/diatomite photocatalyst displayed narrower bandgap (2.95 eV) compared to undoped sample (3.13 eV) and other doped samples (3.05 eV) with higher doping concentration. The photocatalytic activities of V doped TiO{sub 2}/diatomite samples for the degradation of Rhodamine B under stimulated solar light illumination were significantly improved compared with the undoped sample. In our case, V{sup 4+} ions incorporated in TiO{sub 2} lattice were responsible for increased visible-light absorption and electron transfer to oxygen molecules adsorbed on the surface of TiO{sub 2} to produce superoxide radicals ·O{sub 2}{sup –}, while V{sup 5+} species presented on the surface of TiO{sub 2} particles in the form of V{sub 2}O{sub 5} contributed to e{sup –}–h{sup +} separation. In addition, due to the combination of diatomite as support, this hybrid photocatalyst could be separated from solution quickly by natural settlement and exhibited good reusability.

  10. The impact of sodium on the sub-bandgap states in CZTSe and CZTS

    Science.gov (United States)

    Gershon, By Talia; Lee, Yun Seog; Mankad, Ravin; Gunawan, Oki; Gokmen, Tayfun; Bishop, Doug; McCandless, Brian; Guha, Supratik

    2015-03-01

    We compare the optically active sub-bandgap states in polycrystalline Cu2ZnSnSe4 (CZTSe) and Cu2ZnSnS4 (CZTS) thin films as a function of sodium content. In all samples studied, we find that CZTSe has a lower concentration of radiative defect-derived states compared to CZTS and that the states are also shallower in CZTSe compared to CZTS. Further, we find that sodium impacts the relative ratios of two sub-bandgap peaks in the 4 K photoluminescence (PL) spectra of CZTSe (one at ˜0.85 eV and another at ˜0.92 eV). We propose that both of these sub-bandgap peaks stem from intrinsic point defects in CZTSe rather than from electronic states introduced by sodium; this is supported by a measurement on a sodium-free single-crystal of CZTSe. We also show that films with stronger emission through the shallower sub-bandgap states at 4 K display room-temperature PL closer to the bandgap energy. For all sodium quantities studied, one broad PL peak is observed in the 4 K PL spectrum of CZTS which also shifts towards the band edge with increasing sodium. A reduced overall defect density and the fact that the states that are present are shallower together may help account for the lower VOC deficits in CZTSe and the empirical observations that sodium improves device performance.

  11. Fast-light Assisted Four-Wave-Mixing in Photonic Bandgap

    CERN Document Server

    Feng, Cheng; Zhang, Liang; Liu, Jinmei; Zhan, Li

    2014-01-01

    Since the forward and backward waves are coupled with each other and a standing wave with no net propagation of energy is formed in the photonic bandgap, it is a commonsense of basic physics that, any kinds of effects associated with wave propagation including four-wave-mixing (FWM) are thought to be impossible. However, we lay great emphasis here on explaining that this commonsense could be broken under specific circumstances. In this article, we report with the first experimental observation of the energy conversion in the photonic bandgap into other channel via FWM. Owing to the phase manipulation by fast light effect in the photonic bandgap, we manage to achieve the phase-match condition and thus occurred FWM transfer energy into other channels outside the photonic bandgap efficiently. As one-dimensional photonic crystal, simulations on fiber Bragg grating (FBG) with and without fast light were conducted respectively, and an enhanced FWM in photonic bandgap of FBG was observed. The experimental result sho...

  12. Universal rule on chirality-dependent bandgaps in graphene antidot lattices.

    Science.gov (United States)

    Liu, Xiaofei; Zhang, Zhuhua; Guo, Wanlin

    2013-04-22

    Graphene with periodically patterned antidots has attracted intense research attention as it represents a facile route to open a bandgap for graphene electronics. However, not all graphene antidot lattices (GALs) can open a bandgap and a guiding rule is missing. Here, through systematic first-principles calculations, it is found that bandgaps in triangular GALs are surprisingly well defined by a chirality vector R = n a1 + ma2 connecting two neighboring antidots, where a1 and a2 are the basis vectors of graphene. The bandgap opens in the GALs with (n-m)mod3 = 0 but remains closed in those with (n-m)mod3 = ±1, reminiscent of the gap-chirality rule in carbon nanotubes. Remarkably, the gap value in GALs allows ample modulation by adjusting the length of chirality vectors, shape and size of the antidots. The gap-chirality relation in GALs stems from the chirality-dependent atomic structures of GALs as revealed by a super-atom model as well as Clar sextet analyses. This chirality-dependent bandgap is further shown to be a generic behavior in any parallelogram GAL and thus serves as an essential stepping stone for experimenters to realize graphene devices by antidot engineering.

  13. Basic Research of Self-Organized Quantum Dots and Their Potential In Solar Cells and Novel Devices Applications (Phase 4)

    Science.gov (United States)

    2006-01-01

    addition, InP quantum dots are also another candidate for high efficiency quantum dot solar cells due to their wider bandgap which gives better response...at visible region of solar spectrum. However, novel epitaxial growth of high density InP quantum dots with appropriate capping layers is needed to...improvement. We are looking forward to studying InP quantum dots for new structure of quantum dot molecule solar cells having higher open- circuit voltage

  14. Ultrawide-Bandgap Semiconductors: Research Opportunities and Challenges

    Science.gov (United States)

    2017-02-03

    wires in the public domain: https://pixabay.com/p-1587982/?no_redirect. 8. Photo of solar photovoltaic panels in the public domain: https://c2... angle ) for the relatively simple homoepitaxial growth of AlN, all for the same nominal growth conditions.[43-44, 46-47] Moreover, since the...challenge, Figure 4 shows results from the growth of AlGaN films on two substrates with different offcut angles : one has a uniform composition, while

  15. Powerful narrow linewidth random fiber laser

    Science.gov (United States)

    Ye, Jun; Xu, Jiangming; Zhang, Hanwei; Zhou, Pu

    2017-03-01

    In this paper, we demonstrate a narrow linewidth random fiber laser, which employs a tunable pump laser to select the operating wavelength for efficiency optimization, a narrow-band fiber Bragg grating (FBG) and a section of single mode fiber to construct a half-open cavity, and a circulator to separate pump light input and random lasing output. Spectral linewidth down to 42.31 GHz is achieved through filtering by the FBG. When 8.97 W pump light centered at the optimized wavelength 1036.5 nm is launched into the half-open cavity, 1081.4 nm random lasing with the maximum output power of 2.15 W is achieved, which is more powerful than the previous reported results.

  16. Exciton absorption in narrow armchair graphene nanoribbons

    Science.gov (United States)

    Monozon, B. S.; Schmelcher, P.

    2016-11-01

    We develop an analytical approach to the exciton optical absorption for narrow gap armchair graphene nanoribbons (AGNR). We focus on the regime of dominant size quantization in combination with the attractive electron-hole interaction. An adiabatic separation of slow and fast motions leads via the two-body Dirac equation to the isolated and coupled subband approximations. Discrete and continuous exciton states are in general coupled and form quasi-Rydberg series of purely discrete and resonance type character. The corresponding oscillator strengths and widths are derived. We show that the exciton peaks are blue-shifted, become broader and increase in magnitude upon narrowing the ribbon. At the edge of a subband the singularity related to the 1D density of states is transformed into finite absorption via the presence of the exciton. Our analytical results are in good agreement with those obtained by other methods including numerical approaches. Estimates of the expected experimental values are provided for realistic AGNR.

  17. Material and Optical Design Rules for High Performance Luminescent Solar Concentrators

    Science.gov (United States)

    Bronstein, Noah Dylan

    This dissertation will highlight a path to achieve high photovoltaic conversion efficiency in luminescent solar concentrators, devices which absorb sunlight with a luminescent dye and then re-emit it into a waveguide where it is ultimately collected by a photovoltaic cell. Luminescent concentrators have been studied for more than three decades as potential low-cost but not high efficiency photovoltaics. Astute application of the blackbody radiation law indicates that photonic design is necessary to achieve high efficiency: a reflective filter must be used to trap luminescence at all angles while allowing higher energy photons to pass through. In addition, recent advances in the synthesis of colloidal nanomaterials have created the possibility for lumophores with broad absorption spectra, narrow-bandwidth emission, high luminescence quantum yield, tunable Stokes shifts and tunable Stokes ratios. Together, these factors allow luminescent solar concentrators to achieve the optical characteristics necessary for high efficiency. We have fabricated and tested the first generation of these devices. Our experiments demonstrate that the application of carefully matched photonic mirrors and luminescent quantum dots can allow luminescent concentration factors to reach record values while maintaining high photon collection efficiency. Finally, the photonic mirror dramatically mitigates the negative impact of scattering in the waveguide, allowing efficient photon collection over distances much longer than the scattering length of the waveguide. After demonstrating the possibility for high performance, we theoretically explore the efficacy of luminescent concentrators with dielectric reflectors as the high-bandgap top-junctions in two-junction devices. Simple thermodynamic calculations indicate that this approach can be nearly as good as a traditional vertically stacked tandem. The major barriers to such a device are the optical design of narrow-bandwidth, angle

  18. Narrow optical filtering with plasmonic nanoshells

    CERN Document Server

    Martynov, Y B; Tanachev, I A; Gladyshev, P P

    2011-01-01

    Narrow optical band pass filters are widely used in systems with optical processing of information, color displays development and optical computers. We show that such ultra filters can be created by means of nanoparticles which consist of a dielectric sphere and a metallic shell. The components can be adjusted such that there is a remarkable transparency at the desired wavelength range, while a strong absorption takes place outside of this region.

  19. Code optimizations for narrow bitwidth architectures

    OpenAIRE

    Bhagat, Indu

    2012-01-01

    This thesis takes a HW/SW collaborative approach to tackle the problem of computational inefficiency in a holistic manner. The hardware is redesigned by restraining the datapath to merely 16-bit datawidth (integer datapath only) to provide an extremely simple, low-cost, low-complexity execution core which is best at executing the most common case efficiently. This redesign, referred to as the Narrow Bitwidth Architecture, is unique in that although the datapath is squeezed to 16-bits...

  20. Band Gap Narrowing in Heavily Doped Silicon.

    Science.gov (United States)

    Gupta, Tapan Kumar

    Two analytic models for transport and band gap narrowing in heavily doped (N_{rm D} > 10^{20} cm^ {-3}) silicon have been set up and verified through measurements on n^{+} -p junction devices. The first model is based on calculation of the ratio of the charge present in the emitter of the n^{+} region of the junction to that of the charge present in the absence of band gap shrinkage. Fermi-Dirac statistics are employed and are found to have a significant effect at this doping level. The second model is based on current transport of minority carriers in the n^{+} region. In this model only two parameters need to be known, the diffusion coefficient and the diffusion length for minority carriers, to calculate the band gap narrowing. An empirical relation between band gap narrowing and donor concentration has also been established based on experimental values of diffusion coefficient and mobility. These models have been verified by several different experimental techniques including surface photovoltage, open circuit voltage decay, photoconductivity decay and modulation reflection spectroscopy. The results indicate that, in the impurity range above about 10^{20} cm^{-3}, Fermi-Dirac statistics must be invoked in order to achieve a satisfactory fit with experimental data.

  1. Optimization of Organic Solar Cells: Materials, Devices and Interfaces

    Science.gov (United States)

    Zhou, Nanjia

    Due to the increasing demand for sustainable clean energy, photovoltaic cells have received intensified attention in the past decade in both academia and industry. Among the types of cells, organic photovoltaic (OPV) cells offer promise as alternatives to conventional inorganic-type solar cells owning to several unique advantages such as low material and fabrication cost. To maximize power conversion efficiencies (PCEs), extensive research efforts focus on frontier molecular orbital (FMO) energy engineering of photoactive materials. Towards this objective, a series of novel donor polymers incorporating a new building block, bithiophene imide (BTI) group are developed, with narrow bandgap and low-lying highest occupied molecular orbital (HOMO) energies to increase short circuit current density, Jsc, and open circuit voltage, Voc.. Compared to other PV technologies, OPVs often suffer from large internal recombination loss and relatively low fill factors (FFs) thin film morphology, OPVs with PCEs up to 8.7% and unprecedented FF approaching 80% are obtained. Such high FF are close to those typically achieved in amorphous Si solar cells. Systematic variations of polymer chemical structures lead to understanding of structure-property relationships between polymer geometry and the resulting blend film morphology characteristics which are crucial for achieving high local mobilities and long carrier lifetimes. Instead of using fullerene as the acceptors, an alternative type of OPV is developed employing a high electron mobility polymer, P(NDI2OD-T2), as the acceptor. To improve the all-polymer blend film morphology, the influence of basic solvent properties such as solvent boiling point and solubility on polymer phase separation and charge transport properties is investigated, yielding to a high PCE of 2.7% for all-polymer solar cells. To take advantages of the inherent mechanical flexibility associated with organic materials, the development of transparent, flexible

  2. Theoretical analysis of the crystal structure, band-gap energy, polarization, and piezoelectric properties of ZnO-BeO solid solutions

    Science.gov (United States)

    Dong, L.; Alpay, S. P.

    2011-07-01

    The electrical properties, the spontaneous polarization, and the piezoelectric response of ZnO can be tailored by alloying ZnO with BeO for applications such as electrodes in flat panel displays and solar cells, blue and ultraviolet (UV) light emitting devices, and highly sensitive UV detectors. We present here the results of a study that employs density-functional theory to analyze the crystal structure, the band structure, spontaneous polarization, and piezoelectric properties of Zn1-xBexO solid solutions. Our findings indicate that Zn1-xBexO alloys may have a different crystal structure than the end components ZnO and BeO that crystallize in the prototypical wurtzite structure (P63mc). It is shown that orthorhombic lattices with Pmn21, Pna21, or P21 structures may have lower formation energies than the wurtzite lattice at a given Be composition. The band-gap energies of Zn1-xBexO in the wurtzite and the orthorhombic structures are nearly identical and the bowing of the band-gap energy increases with increasing Be concentration. The spontaneous polarization of Zn1-xBexO in the orthorhombic lattice is markedly larger compared to the wurtzite structure while the piezoelectric polarization in the wurtzite and orthorhombic structures varies linearly with the Be concentration.

  3. Electric gating induced bandgaps and enhanced Seebeck effect in zigzag bilayer graphene ribbons

    Science.gov (United States)

    Vu, Thanh-Tra; Tran, Van-Truong

    2016-08-01

    We theoretically investigate the effect of a transverse electric field generated by side gates and a vertical electric field generated by top/back gates on energy bands and transport properties of zigzag bilayer graphene ribbons (Bernal stacking). Using atomistic tight binding calculations and Green’s function formalism we demonstrate that a bandgap is opened when either field is applied and even enlarged under simultaneous influence of the two fields. Interestingly, although vertical electric fields are widely used to control the bandgap in bilayer graphene, here we show that transverse fields exhibit a more positive effect in terms of modulating a larger range of bandgap and retaining good electrical conductance. The Seebeck effect is also demonstrated to be enhanced strongly—by about 13 times for a zigzag bilayer graphene ribbon with 16 chain lines. These results may motivate new designs of devices made of bilayer graphene ribbons using electric gates.

  4. Fabrication and characterization of porous-core honeycomb bandgap THz fibers

    DEFF Research Database (Denmark)

    Bao, Hualong; Nielsen, Kristian; Rasmussen, Henrik K.

    We have fabricated a porous-core honeycomb fiber in the cyclic olefin copolymer (COC) Topas® by drill-draw technology [1]. A cross-sectional image of the fabricated fiber is shown in the left Panel of Fig. 1. Simulation of the electromagnetic properties of the fiber shows two wide bandgaps within...... the cladding modes from the fiber. The propagation loss is measured in a cut-back experiment. The fundamental bandgap at 0.75-1.05 THz is found to have losses lower than 1.5 dB/cm, whereas the loss is below 1.0 dB/cm in the reduced bandgap 0.78-1.02 THz, as shown in Fig. 1(g)....

  5. Tailoring the optical bandgap and magnetization of cobalt ferrite thin films through controlled zinc doping

    Directory of Open Access Journals (Sweden)

    Deepanshu Sharma

    2016-08-01

    Full Text Available In this report, the tuning of the optical bandgap and saturation magnetization of cobalt ferrite (CFO thin films through low doping of zinc (Zn has been demonstrated. The Zn doped CFO thin films with doping concentrations (0 to 10% have been synthesized by ultrasonic assisted chemical vapour deposition technique. The optical bandgap varies from 1.48 to 1.88 eV and saturation magnetization varies from 142 to 221 emu/cc with the increase in the doping concentration and this change in the optical and magnetic properties is attributed to the change in the relative population of the Co2+ at the tetrahedral and octahedral sites. Raman study confirms the decrease in the population of Co2+ at tetrahedral sites with controlled Zn doping in CFO thin films. A quantitative analysis has been presented to explain the observed variation in the optical bandgap and saturation magnetization.

  6. Self-collimated waveguide bends and partial bandgap reflection of photonic crystals with parallelogram lattice.

    Science.gov (United States)

    Gao, Dingshan; Zhou, Zhiping; Citrin, David S

    2008-03-01

    The photonic crystal structure with parallelogram lattice, capable of bending a self-collimated wave with free angles and partial bandgap reflection, is presented. The equifrequency contours show that the direction of the collimation wave can be turned by tuning the angle between the two basic vectors of the lattice. Acute, right, and obtuse angles of collimating waveguide bends have been realized by arc lattices of parallelogram photonic crystals. Moreover, partial bandgap reflection of the parallelogram lattice photonic crystals is validated from the equifrequency contours and the projected band structures. A waveguide taper based on this partial bandgap reflection is also designed and proved to have above 85% transmittance over a very wide operating bandwidth of 180 nm.

  7. Wide bandgap n-type and p-type semiconductor porous junction devices as photovoltaic cells

    Energy Technology Data Exchange (ETDEWEB)

    Lin, Yuan-Pai; Horng, Sheng-Fu [Institute of Electronics Engineering, National Tsing Hua University, Hsinchu 300, Taiwan (China); Chao, Yu-Chiang; Meng, Hsin-Fei [Institute of Physics, National Chiao Tung University, Hsinchu 300, Taiwan (China); Zan, Hsiao-Wen, E-mail: yuchiangchao@gmail.com, E-mail: meng@mail.nctu.edu.tw [Department of Photonics and Institute of Electro-Optical Engineering, National Chiao Tung University, Hsinchu 300, Taiwan (China)

    2011-10-12

    In junction absorber photovoltaics doped wide bandgap n-type and p-type semiconductors form a porous interpenetrating junction structure with a layer of low bandgap absorber at the interface. The doping concentration is high enough such that the junction depletion width is smaller than the pore size. The highly conductive neutral region then has a dentrite shape with fingers reaching the absorber to effectively collect the photo-carriers swept out by the junction electric field. With doping of 10{sup 19} cm{sup -3} corresponding to a depletion width of 25 nm, pore size of 32 nm, absorber thickness close to exciton diffusion length of 17 nm, absorber bandgap of 1.4 eV and carrier mobility over 10{sup -5} cm{sup 2} V{sup -1} s{sup -1}, numerical calculation shows the power conversion efficiency is as high as 19.4%. It rises to 23% for a triplet exciton absorber.

  8. Tuning the hybridization bandgap by meta-molecules with in-unit interaction

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Yongqiang; Li, Yunhui, E-mail: liyunhui@tongji.edu.cn; Wu, Qian; Jiang, Haitao; Zhang, Yewen; Chen, Hong [Key Laboratory of Advanced Micro-Structured Materials, Ministry of Education, School of Physics Science and Engineering, Tongji University, Shanghai 200092 (China)

    2015-09-07

    In this paper, we demonstrate that the hybridization bandgap (HBG) can be tuned conveniently by deep subwavelength meta-molecules with in-unit interaction. Spontaneous-emission-cancellation-like (SEC-like) effect is realized in a meta-molecule by introducing the destructive interference of two detuned meta-atoms. The meta-atoms consisting of subwavelength zero-index-metamaterial-based resonators are side-coupled to a microstrip. Compared to conventional HBG configurations, the presence of in-unit interaction between meta-atoms provides more flexibility in tuning the bandgap properties, keeping the device volume almost unchanged. Both numerical simulations and microwave experiments confirm that the width, depth, and spectrum shape of HBG can be tuned by simply introducing SEC-like interaction into the meta-molecule. Due to these features, our design may be promising to be applied in microwave or optics communications systems with strict limitation of device volume and flexible bandgap properties.

  9. Reversed dispersion slope photonic bandgap fibers for broadband dispersion control in femtosecond fiber lasers.

    Science.gov (United States)

    Várallyay, Z; Saitoh, K; Fekete, J; Kakihara, K; Koshiba, M; Szipocs, R

    2008-09-29

    Higher-order-mode solid and hollow core photonic bandgap fibers exhibiting reversed or zero dispersion slope over tens or hundreds of nanometer bandwidths within the bandgap are presented. This attractive feature makes them well suited for broadband dispersion control in femtosecond pulse fiber lasers, amplifiers and optical parametric oscillators. The canonical form of the dispersion profile in photonic bandgap fibers is modified by a partial reflector layer/interface placed around the core forming a 2D cylindrical Gires-Tournois type interferometer. This small perturbation in the index profile induces a frequency dependent electric field distribution of the preferred propagating higher-order-mode resulting in a zero or reversed dispersion slope.

  10. Energy bandgap variation in oblique angle-deposited indium tin oxide

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Kyurin; Kim, Hyunsoo; Cho, Jaehee, E-mail: jcho@chonbuk.ac.kr [School of Semiconductor and Chemical Engineering, Semiconductor Physics Research Center, Chonbuk National University, Jeonju 561-756 (Korea, Republic of); Park, Jun Hyuk; Kim, Jong Kyu [Department of Materials Science and Engineering, Pohang University of Science and Technology, Pohang 54896 (Korea, Republic of); Fred Schubert, E. [Future Chips Constellation, Department of Electrical, Computer, and Systems Engineering, Rensselaer Polytechnic Institute, Troy, New York 12180 (United States)

    2016-01-25

    Indium tin oxide (ITO) thin films deposited using the oblique angle deposition (OAD) technique exhibit a strong correlation between structural and optical properties, especially the optical bandgap energy. The microstructural properties of ITO thin films are strongly influenced by the tilt angle used during the OAD process. When changing the tilt angle, the refractive index, porosity, and optical bandgap energy of ITO films also change due to the existence of a preferential growth direction at the interface between ITO and the substrate. Experiments reveal that the ITO film's optical bandgap varies from 3.98 eV (at normal incident deposition) to 3.87 eV (at a 60° tilt angle)

  11. Hybrid bandgap engineering for super-hetero-epitaxial semiconductor materials, and products thereof

    Science.gov (United States)

    Park, Yeonjoon (Inventor); Choi, Sang H. (Inventor); King, Glen C. (Inventor); Elliott, James R. (Inventor)

    2012-01-01

    "Super-hetero-epitaxial" combinations comprise epitaxial growth of one material on a different material with different crystal structure. Compatible crystal structures may be identified using a "Tri-Unity" system. New bandgap engineering diagrams are provided for each class of combination, based on determination of hybrid lattice constants for the constituent materials in accordance with lattice-matching equations. Using known bandgap figures for previously tested materials, new materials with lattice constants that match desired substrates and have the desired bandgap properties may be formulated by reference to the diagrams and lattice matching equations. In one embodiment, this analysis makes it possible to formulate new super-hetero-epitaxial semiconductor systems, such as systems based on group IV alloys on c-plane LaF.sub.3; group IV alloys on c-plane langasite; Group III-V alloys on c-plane langasite; and group II-VI alloys on c-plane sapphire.

  12. A Unified Understanding of the Thickness-Dependent Bandgap Transition in Hexagonal Two-Dimensional Semiconductors.

    Science.gov (United States)

    Kang, Joongoo; Zhang, Lijun; Wei, Su-Huai

    2016-02-18

    Many important layered semiconductors, such as hexagonal boron nitride (hBN) and transition-metal dichalcogenides (TMDs), are derived from a hexagonal lattice. A single layer of such hexagonal semiconductors generally has a direct bandgap at the high-symmetry point K, whereas it becomes an indirect, optically inactive semiconductor as the number of layers increases to two or more. Here, taking hBN and MoS2 as examples, we reveal the microscopic origin of the direct-to-indirect bandgap transition of hexagonal layered materials. Our symmetry analysis and first-principles calculations show that the bandgap transition arises from the lack of the interlayer orbital couplings for the band-edge states at K, which are inherently weak because of the crystal symmetries of hexagonal layered materials. Therefore, it is necessary to judiciously break the underlying crystal symmetries to design more optically active, multilayered semiconductors from hBN or TMDs.

  13. EDITORIAL Solar harvest Solar harvest

    Science.gov (United States)

    Demming, Anna

    2010-12-01

    into the charge transport mechanism and trap distribution in these composites [3]. An advantage of investigating solar cell technology based on organic materials rather than silicon is that silicon photovoltaics requires high-purity silicon, whereas the material demands of organic technology are not nearly so strict. Work by researchers in Denmark and Germany highlights the simplicity and tolerance to ambient conditions of organic photovoltaic fabrication in the demonstration of a nanostructured polymer solar cell made from a thermocleavable polymer material and zinc oxide nanoparticles. All the manipulations during device preparation could be carried out in air at around 20 °C and 35% humidity [4]. A possible route to enhancing cell performance is through the improvment of the transport efficiency. Researchers in Taiwan demonstrate how effectively this can be implemented in a hybrid device comprising TiO2 nanorods and poly[2-methoxy-5-(2-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) [5]. In addition, inorganic semiconductor nanocrystals that have tunable optical bandgaps can be combined with organic semiconductors for the fabrication of hybrid photovoltaic devices with broad spectral sensitivity. A collaboration of researchers in the UK and the US has now developed a near-infrared sensitive hybrid photovoltaic system with PbS nanocrystals and C60. The reported improvement in device performance is attributed to increased carrier mobility of the PbS nanocrystal film [6]. In this issue, Patrick G Nicholson and Fernando A Castro from the National Physical Laboratory in the UK present a topical review on the principles and techniques for the characterization of organic photovoltaics [7]. The review presents a comprehensive picture of the current state-of-the-art understanding of the working mechanisms behind organic solar cells, and also describes electronic morphological considerations relevant to optimizing the devices, as well as different nanoscale techniques for

  14. Computational screening of perovskite metal oxides for optimal solar light capture

    DEFF Research Database (Denmark)

    Castelli, Ivano Eligio; Olsen, Thomas; Datta, Soumendu

    2012-01-01

    One of the possible solutions to the world’s rapidly increasing energy demand is the development of new photoelectrochemical cells with improved light absorption. This requires development of semiconductor materials which have appropriate bandgaps to absorb a large part of the solar spectrum...

  15. Photoconductivity of Quantum Dot Films Towards Third-Generation Solar Cells

    NARCIS (Netherlands)

    Talgorn E.C.V.

    2010-01-01

    Colloidal semiconductor nanoparticles, also called quantum dots, have unique opto-electronic properties that make them promising candidates for many applications such as solar cells, light–emitting diodes, lasers, or biological imaging. One of the most interesting features is that the bandgap energy

  16. An efficient method of DFT/LDA band-gap correction

    Science.gov (United States)

    Scharoch, Pawel; Winiarski, Maciej

    2013-12-01

    It has been shown that the underestimated by DFT/LDA(GGA) band-gap can be efficiently corrected by an averaging procedure of transition energies over a region close to the direct band-gap transition, which we call the Δ(EIG) method (the differences in the Kohn-Sham eigenvalues). For small excitations the averaging appears to be equivalent to the Δ(SCF) approach (differences in the self-consistent energies), which is a consequence of Janak’s theorem and has been confirmed numerically. The Gaussian distribution in k-space for electronic excitation has been used (occupation numbers in the Δ(SCF) or eigenenergy sampling in the Δ(EIG)). A systematic behavior of the k-space localization parameter σk correcting the band-gap has been observed in numerical experiments. On that basis some sampling schemes for band-gap correction have been proposed and tested in the prediction of the band-gap behavior in InxGa(1-x)N semiconducting alloy, and a very good agreement with independent calculations has been obtained. In the context of the work the issue of electron localization in the r-space has been discussed which, as it has been predicted by Mori-Sánchez et al. [P. Mori-Sánchez, A.J. Cohen, W. Yang, Phys. Rev. Lett. 100 (2008) 146401], should reduce the effect of the convex behavior of the LDA/GGA functionals and improve the band-gap prediction within DFT/LDA(GGA). A scheme for electron localization in r-space has been suggested.

  17. Investigation of Indoor Stability Testing of Polymer Solar Cell

    Directory of Open Access Journals (Sweden)

    Pelin Kavak

    2016-01-01

    Full Text Available We have fabricated organic solar cell of a new low bandgap polymer poly[4,4-bis(2-ethylhexyl-4H-cyclopenta[2,1-b:3,4-b′]dithiophene-2,6-diyl-alt-4,7-bis(2-thienyl-2,1,3-benzothiadiazole-5′,5′′-diyl] (PCPDTTBTT. We have investigated for the first time the stability tests, ISOS-L-1 and ISOS-D-3, of PCPDTTBTT solar cells. Thermal annealing of PCPDTTBTT solar cells at 80°C brought about an improvement of photocurrent generation, stability, and efficiency of the solar cells. T80 value of PCPDTTBTT solar cell is about 150 hours which is close to P3HT (235 h. PCPDTTBTT is very promising polymer for both polymer solar cell efficiency and stability.

  18. Impact of the deposition conditions of buffer and windows layers on lowering the metastability effects in Cu(In,Ga)Se2/Zn(S,O)-based solar cell

    Science.gov (United States)

    Naghavi, Negar; Hildebrandt, Thibaud; Bouttemy, Muriel; Etcheberry, Arnaud; Lincot, Daniel

    2016-02-01

    The highest and most reproducible (Cu(In,Ga)Se2 (CIGSe) based solar-cell efficiencies are obtained by use of a very thin n-type CdS layer deposited by chemical bath deposition (CBD). However because of both Cadmium's adverse environmental impact and the narrow bandgap of CdS (2.4-2.5 eV) one of the major objectives in the field of CIGSe technology remains the development and implementation in the production line of Cd-free buffer layers. The CBDZn( S,O) remains one the most studied buffer layer for replacing the CdS in Cu(In,Ga)Se2-based solar cells and has already demonstrated its potential to lead to high-efficiency solar cells up to 22.3%. However one of the key issue to implement a CBD-Zn(S,O) process in a CIGSe production line is the cells stability, which depends both on the deposition conditions of CBD-Zn(S,O) and on a good band alignment between CIGSe/Zn(S,O)/windows layers. The most common window layers applied in CIGSe solar cells consist of two layers : a thin (50-100 nm) and highly resistive i-ZnO layer deposited by magnetron sputtering and a transparent conducting 300-500 nm ZnO:Al layer. In the case of CBD-Zn(S,O) buffer layer, the nature and deposition conditions of both Zn(S,O) and the undoped window layer can strongly influence the performance and stability of cells. The present contribution will be specially focused on the effect of condition growth of CBD-Zn(S,O) buffer layers and the impact of the composition and deposition conditions of the undoped window layers such as ZnxMgyO or ZnxSnyO on the stability and performance of these solar cells.

  19. Tuning the band gap of PbCrO{sub 4} through high-pressure: Evidence of wide-to-narrow semiconductor transitions

    Energy Technology Data Exchange (ETDEWEB)

    Errandonea, D., E-mail: daniel.errandonea@uv.es [Departamento de Física Aplicada-ICMUV, Universitat de València, MALTA ConsoliderTeam, C/Dr. Moliner 50, 46100 Burjassot (Spain); Bandiello, E.; Segura, A. [Departamento de Física Aplicada-ICMUV, Universitat de València, MALTA ConsoliderTeam, C/Dr. Moliner 50, 46100 Burjassot (Spain); Hamlin, J.J.; Maple, M.B. [Department of Physics, University of California, San Diego, La Jolla, CA 92093 (United States); Rodriguez-Hernandez, P.; Muñoz, A. [Departamento de Física Fundamental II, Instituto de Materiales y Nanotecnología, Universidad de La Laguna, MALTA ConsoliderTeam, La Laguna, 38205 Tenerife (Spain)

    2014-02-25

    Highlights: • Electronic and optical properties of PbCrO{sub 4} are studied under compression. • Band-gap collapses are observed and correlated with structural phase transitions. • PbCrO{sub 4} band-gap is reduced from 2.3 to 0.8 eV in a 20 GPa range. • PbCrO{sub 4} is an n-type semiconductor with donor levels associated to Frenkel defects. • A deep-to-shallow donor transformation at HP induces a large resistivity decrease. -- Abstract: The electronic transport properties and optical properties of lead(II) chromate (PbCrO{sub 4}) have been studied at high pressure by means of resistivity, Hall-effect, and optical-absorption measurements. Band-structure first-principle calculations have been also performed. We found that the low-pressure phase is a direct band-gap semiconductor (Eg = 2.3 eV) that shows a high resistivity. At 3.5 GPa, associated to a structural phase transition, a band-gap collapse takes place, becoming Eg = 1.8 eV. At the same pressure the resistivity suddenly decreases due to an increase of the carrier concentration. In the HP phase, PbCrO{sub 4} behaves as an n-type semiconductor, with a donor level probably associated to the formation of oxygen vacancies. At 15 GPa a second phase transition occurs to a phase with Eg = 1.2 eV. In this phase, the resistivity increases as pressure does probably due to the self-compensation of donor levels and the augmentation of the scattering of electrons with ionized impurities. In the three phases the band gap red shifts under compression. At 20 GPa, Eg reaches a value of 0.8 eV, behaving PbCrO{sub 4} as a narrow-gap semiconductor.

  20. Ultrasensitive refractive index sensor based on twin-core photonic bandgap fibers

    DEFF Research Database (Denmark)

    Yuan, Scott Wu; Town, Graham E.; Bang, Ole

    We have theoretically investigated twin-core all-solid photonic bandgap fibers (PBGFs) for evanescent wave sensing of refractive index within one single microfluidic analyte channel centered between the two cores. The sensor can achieve ultrahigh sensitivity by detecting the change in transmission....... We find novel features in the sensing characteristics: the sensitivity is higher at the short wavelength edge of a bandgap than at the long wavelength edge, the effective index of the odd supermode (nodd) is more sensitive to ambient refractive index change compared with that of the even supermode...