Timothy Gessert National Renewable Energy Laboratory
Sylvain Marsillac University of Toledo
Takahiro Wada Ryukoku University
Ken Durose Durham University
Clemens Heske University of Nevada-Las Vegas
Y1: Growth and Performance of Compound Thin Film Solar Cells
Tuesday AM, April 10, 2007
Room 2024 (Moscone West)
9:30 AM - **Y1.1
Challenges in Understanding Chalcopyrite Semiconductors for Photovoltaics.
Hans-Werner Schock 1 Show Abstract
1 Solar Energy Technology, Hahn-Meitner-Institut, Berlin Germany
10:00 AM - **Y1.2
Progress in CIGS Solar Cell Processes and Characterization.
Shigeru Niki 1 , Syogo Ishizuka 1 , Kei-ichiro Sakura 1 , Koji Matsubara 1 , Akimasa Yamada 1 , Hitoshi Tampo 1 , Hisayuki Nakanishi 2 , Norio Terada 3 Show Abstract
1 RCPV, AIST, Tsukuba, Ibaraki, Japan, 2 , Tokyo University of Science, Noda, Chiba, Japan, 3 , Kagoshima University, Kagoshima, Kagoshima, Japan
10:30 AM - Y1.3
A Novel Laser-Assisted Deposition Technique for CIGS Thin Films and Solar Cells.
Tokio Nakada 1 , Keita Nozawa 1 , Yasuyuki Ishii 1 Show Abstract
1 Electrical Engineering and Electronics, Aoyama Gakuin University, Sagamihara Japan
High-quality Cu(In1-xGax)Se2 (CIGS) thin films are required for achieving high efficiency thin-film solar cells. This contribution presents a novel laser-assisted-deposition (LAD) technique for improving the crystallographic quality of CIGS thin films and cell performance. In LAD technique a pulse excimer laser (KrF : 248nm, 100Hz) was irradiated onto the substrate surface during CIGS deposition by three-stage process. The crystallographic properties of CIGS thin films grown by three-stage process and LAD were characterized by SEM, TEM and XRD analysis. Time-resolved photoluminescence (TRPL) measurement was also carried out in order to predict a photovoltaic potential of CIGS thin films grown by LAD. The grain size of CIGS thin films became large, and the (112) orientation was enhanced by LAD process. The CIGS deposition was stopped at each step of three-stage process to check the crystallographic properties. As a result, the (InGa)2Se3(110)orientation which leads to the (112) orientation of CIGS was enhanced by the laser irradiation at the 1st step. In contrast, almost no effect was observed when the excimer laser was irradiated at 2nd or 3rd steps. Therefore it becomes evident that the excimer laser irradiation at the first step was most effective to improve the crystalline quality of CIS thin films. TRPL measurement revealed that the PL life time increased from 33 to 45 ns by the laser irradiation during CIGS deposition. This suggests that high efficiency solar cell would be achieved by using LAD process. The solar cells with a ZnO:Al/ZnO/CIGS/Mo/SLG structure were fabricated using two types of CIGS thin films prepared by three-stage process and LAD technique. The average Ga/(In+Ga) determined by ICP (Inductively Coupled Plasma Spectroscopy) was around 0.4. It was found that the open circuit voltage (Voc), fill factor (FF) and the efficiency of the solar cells increased significantly by LAD technique. For instance, a 16.3% efficiency (with Voc=0.659 V, Jsc=34.8 mA/cm2, FF=0.709) was achieved for LAD. It contrasts well with a 14.4 % efficiency (with Voc=0.624 V, Jsc=34.7 mA/cm2, FF=0.662) for three-stage process with the same deposition conditions. This result agrees well with the TRPL data mentioned above. Further experiment was carried out for CIGS thin films with different Ga contents. It was also found that the crystalline quality of CIGS thin films and cell performance were improved by LAD process for all range of Ga content. In conclusion, we found that the LAD process is effective to improve not only crystalline quality of CIGS thin films but also the cell performance.This work was supported in part by NEDO as “R & D for Future technology of PV system”.
10:45 AM - Y1.4
A Liquid Precursor Approach to CuInSe2 Based Photovoltaics.
Jennifer Nekuda 1 2 , Maikel van Hest 2 , Calvin Curtis 2 , Alex Miedaner 2 , Ryan O'Hayre 1 , David Ginley 2 Show Abstract
1 Metallurgy and Materials Engineering, Colorado School of Mines, Golden, Colorado, United States, 2 , National Renewable Energy Laboratory, Golden, Colorado, United States
Tuesday, April 10Transferred Poster Y3.38 to Y1.4 @ 9:45 amA Liquid Precursor Approach to CuInSe2 Based Photovoltaics. Jennifer Ann Nekuda
11:30 AM - **Y1.5
Development of Bi-facial CdTe Solar Cells on Glass and Polymer Substrates.
Genadiy Khripunov 2 , Alessandro Romeo 3 , Hans Zogg 2 , Ayodhya Tiwari 1 2 Show Abstract
2 Thin Film Physics Group, ETH Zurich, Zurich Switzerland, 3 Faculty of Science, University of Verona, 37134 Verona, Italy Italy, 1 Electronic and Electrical Engineering, Loughborough University, Leicestershire United Kingdom
Tueday, April 10New Presentation Time and Paper NumberUpgraded to Invited StatusY1.4 @ 9:45 am to *Y1.5 @ 10:30 amDevelopment of Bi-facial CdTe Solar Cells on Glass and Polymer Substrates. Ayodya Nath Tiwari
12:00 PM - Y1.6
Preparation of Cu(In1-xGax)Se2 Thin Films and Solar Cells Using a Se-radical Beam Source.
Shogo Ishizuka 1 , Akimasa Yamada 1 , Hajime Shibata 1 , Keiichiro Sakurai 1 , Paul Fons 2 , Koji Matsubara 1 , Shigeru Niki 1 Show Abstract
1 Research Center for Photovoltaics, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki Japan, 2 Center for Applied Near-Field Optics Research, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Japan
12:15 PM - Y1.7
Temperature-dependent Degradation Modes in CdS/CdTe Devices.
David Albin 1 , Samuel Demtsu 2 , Anna Duda 1 , Wyatt Metzger 1 Show Abstract
1 PV Devices and Electronic Materials, National Renewable Energy Laboratory, Golden, Colorado, United States, 2 , SoloPower Inc, Milipitas, California, United States
A set of 24 identically made CdTe devices were subjected to accelerated lifetime testing (ALT) using open-circuit bias, 1 sun illumination, and heating under room ambient (dry) conditions at 60, 80, 100, and 120 *C. A total of 6 devices were tested at each temperature. Data was periodically collected for up to 2000+ hours. A systematic pattern of degradation became apparent with increased stress temperature. At 60-80 *C, degradation mechanisms associated with the CdTe/backcontact dominate. In this temperature regime, degradation modes include increased series resistance and increased backcontact barrier height resulting in increased 1st quadrant rollover. As temperature was increased above 80 *C, we observed a significant increase in voltage-dependent collection, which directly affected FF but not Voc. With higher ALT stress temperatures of 100-120 *C, recombination and loss in Voc were the dominant degradation modes. Increased voltage-dependent collection and recombination are believed to be associated with the forward-bias enhanced diffusion of Cu+ from the backcontact to the heterojunction during these ALT studies. This latter understanding was demonstrated by a parallel study using devices in which Cu introduced at the backcontact in a systematically controlled fashion. In these devices, Cu layers of thickness varying from 0 to 100 nm were evaporated onto CdTe devices that had undergone prior nitric-phosphoric etches. This etch produces a Te-rich layer on the surface of the CdTe within which evaporated Cu can react to form CuxTe. Time resolved photoluminescence measurements show a systematic decrease in bulk lifetime near the CdS/CdTe junction with increased evaporated Cu layer thickness. This decrease has been correlated with a decrease in device Voc. Quantum efficiency measurements have also confirmed a decrease in red response with increasing Cu that helps explain the voltage-dependent collection observed in devices stressed at higher ALT temperatures.Further validation of our belief that Cu migration is responsible for degradation modes observed at higher ALT stress temperatures was demonstrated by extracting activation energies from measured degradation rates as a function of time and temperature. Best-fit degradation (D) models using a power law type relationship were used to determine the effective life (L) of devices assuming a 10% drop in efficiency as the "definition" of useable life. Arrhenius-derived activation energies clearly associate an activation energy of 2.8 eV with the lower temperature degradation. The higher temperature activation energy was determined to be 0.63 eV, which agrees well with the literature value of 0.67 eV for Cu diffusion in CdTe. Thus, Cu diffusion is identified as the rate-dominating mechanism for degradation in our CdTe devices stressed at higher ALT temperatures.This abstract is subject to government rights.
12:30 PM - Y1.8
Investigation of ZnO:Al Doping Level and Deposition Temperature Effects on CIGS Solar Cell Performance.
Joel Duenow 1 2 , Timothy Gessert 2 , David Wood 1 , Brian Egaas 1 2 , Rommel Noufi 2 , Timothy Coutts 2 Show Abstract
1 Dept. of Physics, Colorado School of Mines, Golden, Colorado, United States, 2 , National Renewable Energy Laboratory, Golden, Colorado, United States
12:45 PM - Y1.9
InGaAs Solar Cells Grown on Wafer-Bonded InP/Si Epitaxial Templates.
James Zahler 2 , Katsuaki Tanabe 1 , Corinne Ladous 2 , Thomas Pinnington 2 , Frederick Newman 3 , Harry Atwater 1 2 Show Abstract
2 , Aonex Technologies, Pasadena, California, United States, 1 Thomas J. Watson Laboratory of Applied Physics, California Institute of Technology, Pasadena, California, United States, 3 , Emcore Photovoltaics, Albuquerque, New Mexico, United States
Solar cells fabricated on InP/Si epitaxial templates formed by wafer bonding and layer transfer have potential for significant cost and weight reduction relative to cells fabricated on bulk InP substrates. InP/Si substrates could be used as epitaxial templates for InGaAsP/InGaAs dual-junction solar cells lattice-matched to InP as well as conventional InP single-junction cells. Ultimately, InP/Si epitaxial templates are extendable to fabrication of ultrahigh efficiency four-junction (4J) AlInGaP/GaAs/InGaAsP/InGaAs cells via a direct bond interconnect between subcell structures of InGaAsP/InGaAs grown on InP/Si and AlInGaP/GaAs grown on GaAs to form the overall 4J cell structure. In this work we report on the first known demonstration of InGaAs solar cell fabrication on wafer-bonded InP/Si epitaxial templates.InP films ~900 nm thick were transferred onto thermally-oxidized Si substrates via wafer bonding. Transfer of the InP thin film was induced by helium-implantation of the InP and annealing of the bonded InP/Si structure to exfoliate the film. The damaged surface region of the as-transferred InP film was removed using an etching process to leave a film of ~400 nm with a roughness of ~10 nm-rms, as measured by contact mode atomic force microscopy. InGaAs solar cells were grown on the InP/Si epitaxial templates by metalorganic chemical vapor deposition. The solar cells had an n-type InGaAs emitter and a p-type InGaAs base with bandgap energies of 0.74 eV and nominally lattice-matched to (001)InP. Photovoltaic current-voltage (I-V) characteristics of the 1 mm2 InGaAs cells were measured under AM1.5 Global solar spectrum with 1-sun total intensity (100 mW cm-2). For comparison, photovoltaic I-V characteristics of InGaAs cells grown on bulk epi-ready (001)InP substrates were also measured. The device parameters for the InGaAs cell grown on the wafer-bonded InP/Si epitaxial template were Jsc = 35.8 mA cm-2, Voc = 0.29 V, FF = 0.56, and η = 5.8%, where Jsc, Voc, FF and η are short-circuit current, open-circuit voltage, fill factor and energy conversion efficiency, respectively. This performance was comparable to that of the InGaAs cells grown on bulk (001)InP substrates, Jsc = 26.9 mA cm-2, Voc = 0.31 V, FF = 0.63, and η = 5.2%.
Y2: Novel Materials and Processes
Tuesday PM, April 10, 2007
Room 2024 (Moscone West)
2:30 PM - **Y2.1
Issues for Composition Control in the Deposition of CuInSe2-based Alloys.
William Shafarman 1 , Robert Birkmire 1 , Shiro Nishiwaki 1 , Greg Hanket 1 Show Abstract
1 Institute of Energy Conversion, University of Delaware, Newark, Delaware, United States
The composition of Cu(InGa)Se2 thin films grown by elemental evaporation is controlled in a predictable manner by the delivery of the elemental fluxes. Under typical deposition conditions, the Cu and Se are distributed uniformly through the bulk of the film while the Ga and In distributions are determined by their flux–time profiles during growth. However, with different alloys and growth processes the film composition can be controlled by other factors which will be described in this work. The formation of stable intermetallic phases plays a critical role in the growth of CuAlSe2 by elemental evaporation and in the composition control of Cu(InGa)Se2 or Cu(InGa)(SeS)2 by the reaction of metal precursors. In each case, procedures to overcome the formation of the intermetallic phases and form single phase chalcopyrite materials with controlled composition will be described. In the elemental evaporation of CuIn(SeS)2 or Cu(InGa)(SeS)2 the relative incorporation of the chalcogen species is controlled by the presence of excess Cu and the effects of film composition versus relative flux variation will be described.
3:00 PM - Y2.2
Fabrication and Characterization of Cd1-xMgxTe Thin Films and Their Application in Solar Cells
Ramesh Dhere 1 , Kannan Ramanathan 2 , John Scharf 1 , Bobby To 1 , Anna Duda 1 , Helio Moutinho 1 , Rommel Noufi 1 Show Abstract
1 , National Renewable Energy Lab, Golden, Colorado, United States, 2 , MiaSole, Santa Clara, California, United States
Two-junction tandem solar cells require a top cell with a bandgap in the range of 1.6–1.8 eV. Ternary alloys of CdTe are of great interest for this application because of the success of CdTe solar cells. Considerable work has been conducted on Cd1-xZnxTe (CZT) polycrystalline thin films, but the development of CZT solar cells is hampered by the high affinity of Zn to oxygen and chlorine, which are routinely used in fabricating high-efficiency CdTe solar cells. Cd1-xMgxTe (CMT) offers several unique advantages, such as a large change in bandgap for the same composition as compared to CZT. The lattice mismatch between CdTe and CMT is minimal in the entire composition range, and the alloy retains the sphalerite structure of CdTe in a wide composition range. In this paper, we present our work on developing CMT polycrystalline thin films. CMT thin films were fabricated by co-evaporation of CdTe and Mg at a substrate temperature of 400ο C. The spatial separation of the two sources resulted in a compositional gradient, which allowed the deposition of a wide range of compositions from fewer runs. Stable films for compositions up to x=0.73 were fabricated, and the structural properties of the samples were studied by X-ray diffraction. The data show that the films have a sphalerite structure and are preferentially oriented in the <111> direction, and the lattice constant varies linearly with composition. Optical analysis of the samples shows that the optical bandgap varies linearly with composition and can be described byEg(x) = 1.6 x + 1.46 eV.The optical absorption coefficient of the alloy films for the entire composition range (up to x=0.73) is over 6x104/cm for energies above the bandgap, indicating a direct-gap semiconductor. We have fabricated solar cells using these films with the following structure: glass / SnO2 / CdS / CMT / back contact. Using the same processing conditions used for CdTe solar cells, the device efficiency was less than 2%. Post-deposition chloride heat-treatment in oxygen ambient resulted in partial dissociation of the CMT alloy and loss of Mg. With modified contact processing, we were able to improve efficiencies to over 5%. With modified chloride processing, we were able to minimize alloy decomposition and further improve the efficiencies. We have obtained devices with open-circuit voltages of up to 845 mV and efficiencies of 8% for CMT devices with a bandgap in the range of 1.6–1.62 eV. We will present a detailed analysis of the device properties and their correlation to materials properties of CMT. This abstract is subject to government rights.
3:15 PM - Y2.3
Nanostructured ZnS:In2S3 Buffer Layers. Can Voltage and Efficiency be Improved Through Interface Inhomogeneities on a Scale Below the Minority Carrier Diffusion Length?
Nicholas Allsop 1 , Andreas Haensel 1 , Christian Camus 1 , Sophie Gledhill 1 , Iver Lauermann 1 , Christian Fischer 1 , Martha Lux-Steiner 1 Show Abstract
1 Solar Energy - Heterogeneous Material Systems, Hahn-Meitner-Institute, Berlin Germany
3:30 PM - Y2.4
Experimental and Theoretical Study of Fluorine Doping to Tin Oxide.
Xiaonan Li 1 , Sally Asher 1 , Joel Pankow 1 , Lei Kerr 2 , Mailasu Bai 3 , Timothy Gessert 1 Show Abstract
1 5200, National Renewable Energy Laboratory, Golden, Colorado, United States, 2 , Miami University of Ohio, Oxford, Ohio, United States, 3 , Colorado School of Mines, Golden, Colorado, United States
Conductive tin-oxide (SnO2) films on glass substrates are used extensively for transparent electrodes in thin-film photovoltaic solar cells, electrochromic devices, flat-panel displays, and gas sensors. SnO2 with a tetragonal structure is naturally an n-type semiconductor because of a deviation from stoichiometry. The best n-type dopants for SnO2 is fluorine. With it, the electron concentration of 5-10^20/cm^3, and μ of 40 cm^2/V-s has achieved. However, the commonly used fluorine dopant for research used SnO2 film, bromotrifluoromethane (CBrF3), is a green–house gas. Thus, the alternative fluorine source is needed to replace the CBrF3. In this study, we first estimated the doping efficiency for different dopant precursors (CF4, CBrF3, and CIF3). We find that CIF3 is a most reactive precursor in the three precursors that studied. The reactivity of CF4 is much lower than the other two precursors. This prediction is consistent with the experimental observation. Then we did experiments to studied CIF3 source as replacement. The electric and optical properties of the SnO2 film that doped by CBrF3 and CIF3 source are compared. The effects of deposition temperature, different dopant and oxygen gas flow rates are studied. We found that due to the high volatility of CBrF3 precursor, the fluorine doping efficiency is strongly dependent on the substrate temperature and reaction chamber pressure. As a comparison, to achieve the similar carrier concentration, far less CIF3 dopant is required. However, for similar film thickness, with the CIF3 doping, the SnO2 film has lower mobility (<30 cm^2/Vs) and higher optical absorption compared with the films doped with CBrF3.This abstract is subject to government rights.
3:45 PM - Y2.5
Development of a Wide Band Gap Cd1-xMgxTe Film for Applications in Tandem Devices.
Xavier Mathew 1 2 , Anthony Vasko 1 , Jennifer Drayton 1 , Alvin Compaan 1 Show Abstract
1 Physics and Astronomy, Univ. of Toledo, Toledo, Ohio, United States, 2 CIE, UNAM, Temixco, Morelos, Mexico
4:30 PM - **Y2.6
Zn-based Buffer Layer and High-quality CIGS Films Grown by a Novel Method.
Akira Yamada 1 , Fanying Meng 1 , Yoshiyuki Chiba 2 , Makoto Konagai 2 Show Abstract
1 Quantum Nanoelectronics Research Center, Tokyo Institute of Technology, Tokyo Japan, 2 Department of Physical Electronics, Tokyo Institute of Technology, Tokyo Japan
5:00 PM - Y2.7
Growth and Characterization of Chalcopyrite Nanocrystals: Beyond Conventional Thin Films.
David Fuertes Marron 1 , Sebastian Lehmann 1 , Sascha Sadewasser 1 , Martha Ch. Lux-Steiner 1 Show Abstract
1 Department of Solar Energy, Hahn-Meitner Institut, Berlin Germany
5:15 PM - Y2.8
Transparent Back Contacts in CdTe/CdS: Evaluation for Tandem Cells.
Viral Parikh 1 , Anthony Vasko 1 , Alvin Compaan 1 Show Abstract
1 Physics and Astronomy, University of Toledo, Toledo, Ohio, United States
By using a transparent back contact (TBC), a CdTe/CdS cell may be transparent to photons with energy less than the 1.5 eV bandgap of CdTe. This allows CdTe cells to be used as a top cell in a tandem structure, of either the two- or four-terminal kind. We have fabricated CdTe cells with transparent back contacts yielding efficiencies of up to 9%. We have evaluated the back contacts in terms of cell efficiency and transparency using combinations of p-type ZnTe:N and ZnTe:Cu, with n-type ZnO:Al and ITO (for total combinations of ZnTe:N/ZnO:Al, ZnTe:N/ITO, ZnTe:Cu/ZnO:Al, and ZnTe:Cu/ITO). CdTe thicknesses from 0.6 to 2.5 micrometers have been used. CdTe of lesser thickness may transmit some above bandgap photons, allowing for current matching in two terminal devices. We have performed bifacial IV and QE characterization under varying degrees of white light bias. Modeling has been employed to extract information on depletion widths and drift and diffusion lengths, and to understand the impact of TBC materials on the carrier collection from the primary junction. Acknowledgements – This work is supported by the NREL high performance PV program.
5:30 PM - Y2.9
An Indium Free Transparent Conductive Oxide: doped TiO2.
M. van Hest 1 , M. Gillispie 2 , M. Dabney 1 , J. Perkins 1 , D. Ginley 1 Show Abstract
1 , National Renewable Energy Laboratory, Golden, Colorado, United States, 2 , Iowa State University, Ames, Iowa, United States
Most of the commonly used transparent conductive oxides (TCO) contain indium. Due to its cost, there is a clear need for an indium free alternative. Doped anatase TiO2 thin films grown on SrTiO3 (STO) using pulsed laser deposition (PLD) have been shown to be viable In-free transparent conductors with conductivities of 3500-5000 S/cm for 40 nm thick films. Little is known about this material. Here, we will show a detailed study of this material deposited by PLD and sputtering. This study demonstrates that the conductivity in this material is a bulk effect. It is also demonstrated that the TiO2 needs to be biaxially textured (004) anatase in order to be highly conductive. Since PLD is most likely not a viable way of deposition for large area, alternative methods for deposition of this material are studied. It is demonstrated that doped anatase TiO2 films can be deposited by RF magnetron sputtering. Thin films of Ti0.85Nb0.15O2 were deposited on STO and glass substrates using a ceramic oxide target at varying substrate temperatures in a pure Ar atmosphere. For films grown on STO, conductivity as high as 1500 S/cm has been obtained. X-ray diffraction (XRD) analysis showed that the most conductive films were (004)-textured anatase TiO2. Films grown on glass showed a maximum conductivity of ~100 S/cm, 15x smaller than films on STO. This decrease in conductivity is largely due to a decreased mobility. XRD analysis for the most conductive films on glass showed randomly oriented anatase TiO2.
5:45 PM - Y2.10
Towards Lower Deposition Temperatures of Spray Deposited ZnO Films.
Sophie Gledhill 1 , Pablo Thier 1 , Nicholas Allsop 1 , Martha Lux-Steiner 1 , Christian Herbert Fischer 1 Show Abstract
1 Solar Energy 2, Hahn-Meitner Institute, Berlin Germany
Tuesday PM, April 10, 2007
Salon Level (Marriott)
9:00 PM - Y3.1
In-situ Characterization of As-grown Surface of CIGS Films.
Hirotake Kashiwabara 1 , Shimpei Teshima 1 , Kazuya Kikunaga 1 , Kazunori Takeshita 1 , Tetsuji Okuda 1 , Kozo Obara 1 , Keiichiro Sakurai 2 , Shogo Ishizuka 2 , Akimasa Yamada 2 , Koji Matsubara 2 , Shigeru Niki 2 , Norio Terada 1 2 Show Abstract
1 Nano-Structure and Advanced Materials, Kaghosima University, Kagoshima Japan, 2 Research Center for Photovoltaics, National Institute of Advanced Industrial Science and Technology, Tsukuba Japan
Control of hetero interfaces in Cu(In1-xGax)Se2 [CIGS] based solar cells is one of the keys for pursuing higher conversion efficiency. For the interface between CdS buffer grown by chemical bath deposition (CBD) and In-rich CIGS absorber, it has been repeatedly observed that the CIGS region adjacent to the interface has Cu-deficient composition and much wider band gap energy about 1.3 eV, with respect to those of the corresponding bulk. It has been recognized that the presence of this wide gap region would suppress the carrier recombination and cause a notable improvement of cell-performances. Understanding of formation mechanism of the wide gap surface-region of CIGS is, therefore, important for the precise control of the interface. There are, however, few experimental reports about it. Theoretical calculations have indicated the structural instability of stoichiometric surface of CIGS, and stabilization of it by introduction of Cu-vacancies. It suggests the self-formation of Cu-deficient surface during growth process of CIGS. On the other hand, serious modifications of the CIGS surfaces in CBD process is also pointed out, since Cu ions in CIGS could be selectively dissolved in the bath.In order to determine in which sequence the wide gap region is formed, chemical formula and electronic structure of the as-grown CIGS layer by in-situ XPS, UPS and IPES.Specimen films with a nominal composition of Cu0.93(In0.65Ga0.35)Se2 were grown by conventional three stage co-evaporation. They were transported to the analysis system by using a vacuum vessel. During the transportation, pressure of the vessel was maintained at mid 10-9 Torr or better. This method yielded a clean feature of the as-received surfaces; carbon and oxygen were below detection limit of XPS.The as-grown surface exhibited seriously Cu and Ga depleted composition: Cu/(Cu+In+Ga+Se) = 0.08 ~ 0.10, Cu/(In+Ga) = 0.29 ~ 0.31 and Ga/(In+Ga) = 0.15. Though slow increases of these ratios were observed in the depth profile, the region 10 ~ 20 nm under the original surface had Cu/(Cu+In+Ga+Se) = 0.14, Cu/(In+Ga) = 0.40 and Ga/(In+Ga) = 0.38, which are between so-called 1-3-5 and 1-5-8 Cu-deficient phases. These results revealed that the Cu and Ga deficient phase is already formed in the final stage of the growth of CIGS.UPS/IPES measurements of the as-grown surface revealed on expansion of band gap energy up to 1.4 eV and n-type character. In the depth profile of the electronic structure, examined by using a low energy ion etching, a gradual rise of Fermi level was observed.These results mean that the as-grown surface of CIGS by the three stage method already has the wide band gap, n-type electronic structure and Cu-, Ga-deficient composition. They also suggested that the termination method of the CIGS growth should be one of the important factors of the nature of CdS/CIGS interface.
9:00 PM - Y3.10
Compositional Variance of Conductivity in Sputter-Deposited Amorphous Indium Zinc Oxide Transparent Films
Andrew Leenheer 1 2 , John Perkins 2 , Andrew Cavendor 1 2 , Matthew Taylor 2 , Maikel van Hest 2 , Ryan O'Hayre 1 , David Ginley 2 Show Abstract
1 Materials Science, Colorado School of Mines, Golden, Colorado, United States, 2 National Center for Photovoltaics, National Renewable Energy Lab, Golden, Colorado, United States
Due to its high electrical conductivity, high visible-spectrum transparency, smoothness and ease of deposition, amorphous indium zinc oxide (IZO) is a n-type transparent conducting oxide (TCO) of increasing interest for photovoltaic and other optoelectronic applications. IZO thin films deposited by magnetron sputtering are amorphous over the metals-only composition range ~55 to 85 atomic %. In this work, five different single-composition targets spanning the amorphous range were used to sputter thin films on glass and fused silica with varying oxygen content. The resistivity, carrier concentration, and hall mobility were measured for the films, as well as optical transmission and reflection spectra for λ=300-900 nm light. For these IZO films, the conductivity can be controllably varied over six orders of magnitude from ~ 2.5 x 103 S/cm down to ~ 10-3 S/cm depending on the composition and deposition conditions. Adding oxygen to the argon sputtering gas generally lowers the carrier concentration. In addition, the electron mobility increases with lower indium content, while the carrier concentration drops with lower indium content.
9:00 PM - Y3.11
Device Behavior of Cu(InGa)(SeS)2 Solar Cells with >1.5 eV Bandgap.
Shiro Nishiwaki 1 , William Shafarman 1 Show Abstract
1 , Institute of Energy Conversion, Newark, Delaware, United States
9:00 PM - Y3.12
Characterization of ZnO Thin Film Prepared by Solid Source Chemical Vapor Deposition.
Hau-Ting Hu 1 , Yang-Chun Fang 1 , Shih-Hsuan Yang 1 , Liang Chao 1 Show Abstract
1 Electronic Engineering, National Taiwan University of Science and Technology, Taipei Taiwan
9:00 PM - Y3.13
In situ Investigation of Reaction Pathways of Cu-Se, In-Se and Ga-Se Mixed and Bilayer Precursors.
Woo Kyoung Kim 1 , E. Andrew Payzant 2 , Tim Anderson 1 Show Abstract
1 Chemical Engineering, University of Florida, Gainesville, Florida, United States, 2 Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
9:00 PM - Y3.14
First-principles Calculations on Zn1-xMgxO Window Layer for CIS Thin Film Solar Cells.
Tsuyoshi Maeda 1 , Akio Shigemi 1 , Takahiro Wada 1 Show Abstract
1 Materials Chemistry, Ryukoku University, Otsu, Shiga, Japan
9:00 PM - Y3.15
Fabrication of (Cu,Ag)InSe2 Thin films by a Combination of Mechanochemical and Screen Printing/Sintering Processes
Syuusuke Nomura 1 , Yoshihiro Matsuo 1 , Takahiro Wada 1 Show Abstract
1 Materials Chemistry, Ryukoku University, Otsu, Shiga, Japan
CuInSe2 (CIS) and its solid solution such as Cu(In,Ga)Se2 (CIGS) are excellent thin-film photovoltaic materials. The CIGS films are usually deposited by physical vapour deposition (PVD) or sputtering and “selenization”. However, vacuum-based deposition processes, such as PVD and sputtering are complex and expensive. Therefore, some research groups have proposed non-vacuum deposition techniques for CIGS thin films. We have fabricated CIGS thin films by our original non-vacuum process, a combination of mechanochemical and screen printing/sintering processes . Our preliminary CIGS solar cells showed an efficiency of 2.7%. Recently, wide-band-gap Ag(In,Ga)Se2 thin film solar cells with an efficiency of nearly 10% was demonstrated . AgInSe2 has a bang gap (Eg) of 1.24 eV, which is a little wider than Eg of CuInSe2, 1.04 eV. In this study, we fabricated (Cu,Ag)InSe2 (CAIS) thin films by a combination of mechanochemical and screen printing/sintering processes and characterized their properties.
Elemental powders such as Cu, Ag, In, Se were weighted to give a molar ratio of (Cu1-xAgx): In:Se =1:1:2. CAIS powder was synthesized from elemental powders by a planetary ball milling in N2 gas atmosphere. The synthesized powder was determined to be chalcopyrite compound by X-ray powder diffraction using Cu-Kα radiation. Particulate precursors ink was prepared by a mixing of the obtained CAIS powder with an organic solvent. The precursor layer was deposited on a Mo coated soda lime glass substrate by the screen-printing. The organic solvent was removed from the screen-printed CIGS film by the heating in N2 gas atmosphere. Porous precursor layer was sintered into dense polycrystalline films by heat-treatment under an atmospheric-pressure N2 gas atmosphere. Crystal structure of the film was analyzed by x-ray diffraction and the microstructure was observed in a scanning electron microscope (SEM).
The x-ray diffraction patterns of CAIS powders showed characteristic peaks of the chalcopyrite structure such as 101 peak at 2θ=17° and 211 peak at 2θ=35°. The diffraction peaks was shifted low angle with increasing Ag amount. Therefore, we understood that the lattice parameters of CAIS solid solution increased with Ag contents. The particle size distribution measurements showed that the CAIS powders have average particle size of about 1μm. The surface and cross-sectional microstructure of the CAIS film were observed in an SEM. The thickness of the typical film is about 7-10μm, which is a little thicker than the CIGS films fabricated by the PVD or “sputtering and selenization” techniques.
This work was supported by the Incorporated Administrative Agency New Energy and Industrial Technology Development Organization (NEDO) under the Ministry of Economy, Trade and Industry (METI).
 T. Wada et al., phys. stat. sol. (a) 203, 2593-2597 (2006).
 K. Yamada et al., Science and Technology of Advanced Materials 7, 42-45 (2006).
9:00 PM - Y3.16
Validation of the p-type Behavior of an Ag-doped ZnSe Film Grown Heteroepitaxially on GaAs(100) Substrate.
Takashi Narushima 1 , Hiroaki Yanagita 1 , Masahiro Orita 1 Show Abstract
1 R&D Center, HOYA Corporation, Tokyo Japan
9:00 PM - Y3.17
ZnO Thin Films Prepared by Thermal Oxidation of Metallic Zinc Films.
Chon-Chi Liau 1 , Liang Chao 1 Show Abstract
1 Electronic Engineering, National Taiwan University of Science and Technology, Taipei Taiwan
9:00 PM - Y3.18
Synthesis of Size-controlled ZnO Seed for Nanorod Growth and its Application to Solar Cell.
Ki Seok Kim 1 , Gun-Young Jung 1 Show Abstract
1 Material Science & Engineering, Gwnagju Institute of Science & Engineering, Gwangju Korea (the Republic of)
9:00 PM - Y3.19
Study of Band Alignment at CBD-CdS/Cu(In1-xGax)Se2 (x = 0.2 ~ 1.0) Interfaces by Photoemission and Inverse Photoemission Spectroscopy.
Shimpei Teshima 1 , Hirotake Kashiwabara 1 , Keimei Masamoto 1 , Kazuya Kikunaga 1 , Kazunori Takeshita 1 , Tetsuji Okuda 1 , Keiichiro Sakurai 2 , Shogo Ishizuka 2 , Akimasa Yamada 2 , Koji Matsubara 2 , Shigeru Niki 2 , Norio Terada 1 2 Show Abstract
1 Nano-Structure and Advanced Materials, Kagoshima University, Kagoshima Japan, 2 Research Center for Photovoltaics, National Institute of Advanced Industrial Science and Technology, Tsukuba Japan
It is widely recognized that nature of the hetero-interfaces in Cu(In1-xGax)Se2 [CIGS] based solar cells should be one of the keys for pursuing higher conversion efficiency, especially the wide gap CIGS based cells. Direct characterization of changes of electronic structure around the interfaces buried in the cell structure with band gap energy of CIGS should be useful for clarifying of origins of serious deterioration of the cell performances, and for deducing guiding principles towards the improvement. In the present study, we have attempted a characterization of valence- and conduction band alignments at the interfaces between CdS buffer layer grown by chemical bath deposition and CIGS one with Ga substitution ratio x up to 1.0 grown by three stage co-evaporation by means of photoemission and inverse photoemission spectroscopy, and scanning Kelvin probe microscopy.Obtained results so far are summarized as follows.i) a low region of Ga substitution ratio x ~ 0.2; The CIGS region adjacent to the interface had a band gap around 1.3 ~ 1.4 eV, which was much wider than that of bulk-specimen with corresponding composition. VBO and CBO at these interfaces were finite, where the conduction band minimum of CdS located above that of the CIGS (positive CBO). VBO and CBO of the CdS/Cu(In0.80Ga0.20)Se2 specimen were 0.7 and 0.25 eV, respectively. ii) region of x < 0.4; an increase of VBO and a reduction of CBO with a rise of x were observed. CBO reached around 0 ~ -0.15 at the CdS/Cu(In0.55~0.60Ga0.40~0.45)Se2 interface. This result is consistent with the fact that the conversion efficiency of our cells took a maximum around x = 0.3. iii) region of x from 0.5 to 1.0, the CBO continuously decreased. Consequently, CBO was negative over the Ga-rich region including CGS. In this region, the energy spacing between conduction band minimum of CdS and valence band maximum of CIGS gave the minimum of band gap energy in the interface region, which was almost constant over the Ga-rich region. Additionally, in this region of x, oxygen impurities localized at the interface was apparently detected which also should promote decrease of Fermi level. Local enhancement of the negative CBO was observed just at the interface. iv) Depth profiles of work function were consistent with the band alignments at the interface and gradient of conduction band minimum in interior region of CIGS layer. These results are consistent with the saturation tendency of open circuit voltage and a deterioration of conversion efficiency in the wide gap CIGS based cells. The present study indicates usefulness of the direct characterization of the CdS/CIGS interfaces for clarification of the correlation between the interface electronic structure of the CIGS based cells over the wide range of the Ga concentration.
9:00 PM - Y3.2
Room Temperature Growth of Indium Oxide Films by Reactive Ion Beam Assisted Deposition.
Kai Wang 1 , Yuriy Vygranenko 1 , Arokia Nathan 2 Show Abstract
1 Electrical & computer engineering, University of Waterloo, Waterloo, Ontario, Canada, 2 London Center for Nanotechnology, University College London, London United Kingdom
9:00 PM - Y3.20
Characteristics of ZnO thin film Deposited by Atomic Layer Deposition Method.
Jae Sung Hur 1 , Chang-Sik Son 2 , Dong-Gun Lee 1 , Samseok Jang 1 , Jung-Bin Song 1 , In-Hoon Choi 1 , Dongjin Byun 1 , Byoung-Hoon Lee 1 Show Abstract
1 Material science and engineering, Korea Univ., Seoul Korea (the Republic of), 2 Photonics, Silla Univ., Pusan Korea (the Republic of)
9:00 PM - Y3.21
Copper-Indium-Boron-Diselenide Absorber Materials.
Ned Ianno 1 , Tobin Santero 1 , Rodney Soukup 1 , Chrisropher Exstrom 2 , Scott Darveau 2 , Jiri Olejnicek 2 Show Abstract
1 Electrical Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska, United States, 2 Chemistry, University of Nebraska at Kearney, Kearney, Nebraska, United States
One of the most useful thin film solar cell materials is CuInxGa1-xSe2 (CIGS). Although the band gap increases as x increases, the most efficient cells have been produced with x=0.24 with open circuit voltages slightly greater than 1V. Higher values of x result in lower voltage due to changes in the band structure. In order to increase the open circuit voltage we have substituted boron, rather than gallium, for indium and have fabricated novel CuBSe2 (CBS) and CuInxB1-xSe2 (CIBS) materials.. Based on preliminary calculations we have estimated the percentage of boron substitution required to yield a band gap of 1.5 eV in CIBS to be 24%.The precursor copper-indium-boron, CuInxB1-x, films are magnetron co-sputtered onto bare soda-lime glass and Mo coated soda-lime glass, where x has been varied from 1 to 0. The films are selenized in a separate step from a solid selenium source. The resulting films are analyzed by a variety of methods. These methods include characterization by x-ray diffractometry, photon transmission/absorption, Fourier Transform Infrared and Raman spectroscopies and spectroscopic ellipsometry. Spectroscopic results are compared to CIS films deposited in our laboratory and CIGS films reported in the literature. We will show the effect of boron substitution on the lattice parameters, optical band gap, and phonon frequency shift.
9:00 PM - Y3.22
Effect of Bias Light on Photovoltage Decay in CdTe/CdS Solar Cells.
Kent Price 1 Show Abstract
1 , Morehead State University, Morehead, Kentucky, United States
We have measured the open-circuit photovoltage decay of CdTe/CdS solar cells with and without a constant bias-light source. We used red probe light with and without white bias light, and white probe light with and without red bias light. In all cases the voltage decays exponentially with time from approximately 750 mV to zero after the turn-off of the probe light. The decay time depends on the sample and varies from tens of microseconds to milliseconds. With both red and white bias light, the decay is faster in the presence of bias light. In addition, the presence of white bias light results in a small (~3 mV) increase in voltage after the initial decay. The increase occurs over a time-scale of milliseconds. The relatively slow nature of the increase and the fact that it occurs only in the presence of white bias light suggests it is due to a re-arrangement of charge in deep states of the CdS layer. The work therefore adds evidence that photoconductivity in the CdS layer may be important in CdTe/CdS device performance. This work is supported in part by the Kentucky Science and Engineering Foundation.
9:00 PM - Y3.23
All-CSS CdTe Solar-Cell Fabrication Process with Thinner CdS Layers.
Alan Davies 1 , J. Sites 1 , R. Enzenroth 1 Show Abstract
1 , Colorado State University, Fort Collins, Colorado, United States
Cadmium Sulfide/Cadmium Telluride (CdS/CdTe) thin-film solar cells have been fabricated by an in-line, Close-Space-Sublimation (CSS) process at Colorado State University. The goal of the current work is to reduce the CdS layer thickness to achieve high short-circuit current, while maintaining open-circuit voltage and fill factor at the levels typical with thicker CdS. Current-Voltage (J-V) and Quantum Efficiency (QE) measurements showed the expected increase in Jsc due to enhanced blue response as CdS is thinned over a range from 200 to 10 nm. However, thin CdS yielded reduced Voc (800mv for 200 nm CdS, 350mv for 10 nm) and FF (71% to 52%) due to areas of weak-junction formation where CdTe comes into close contact with the SnO2 TCO layer. As a result, gains in Jsc were offset and efficiencies reduced from 12.6% for the thick CdS layer to 4.5% for devices with the thinnest CdS. Localized weak junction formation in cells with thin CdS was characterized by high-resolution Laser-Beam-Induced Current (LBIC) 2-D mapping. Greater incidence of spatial non-uniformities in photocurrent response accompanied thinning of the CdS layer. At 638 nm, photocurrent varied spatially by 1.3% for thin CdS devices compared to 0.3% for thicker CdS. Non-uniformities of cells with thin CdS were highly sensitive to voltage biasing, consistent with the reduced voltages of these devices.
9:00 PM - Y3.24
Optimization Of Electro Deposited In2S3 Buffer Layers In CuInS2 Cells.
Teodor Todorov 1 , Juan Carda 1 , Eloisa Cordoncillo 1 , Purificacion Escribano 1 , Joachim Klaer 2 , Reiner Klenk 2 Show Abstract
1 Inorganic and Organic Chemistry, Universidad Jaume I, Castellón de la Plana, Castellón, Spain, 2 , Hahn-Meitner-Institut , Berlin Germany
Currently the best chalcopyrite photovoltaic cells employ CdS buffers deposited by chemical bath deposition. For large-scale inline production it is desirable to replace both the toxic material and its batch formation route related with low material utilization and necessity to manage large amounts of residual liquids. In the search for alternatives, during the last years significant progress has been made with different materials such as ZnS and In2S3-based materials deposited by atomic layer deposition (ALD), metal organic chemical vapour deposition (MOCVD), ion layer gas reaction (ILGAR), sputtering and thermal evaporation. Nevertheless, all of them either have inconveniencies for industrial application (ALD, ILGAR) or employ vacuum equipment which adds significantly to the production facilities cost. In an attempt to develop a process suitable for low-cost large-scale industrial manufacturing of CuInS2 PV modules, results of our recent work have demonstrated the feasibility of electro deposited In2S3-based buffer layers. Relatively good open-circuit voltage and short-circuit current were obtained, however, the fill factor as well as the deposition reproducibility and homogeneity were not entirely satisfactory. The present contribution reports the different approaches which were undertaken with the objective to improve these properties. The deposition parameters are discussed in relation with film characteristics and solar cell performance. Along with the influence of the starting composition and electro deposition regime, the fluid behavior of the solution was examined and several setup configurations were tested with or without the use of stirring methods. Film deposition proved very sensitive to the flow regime, which was a dominant factor in most cases. When stirring was absent, the convection-driven laminar flow at the substrate surface caused strong gradients in film thickness due to inhomogeneous mass transport and/or electrochemical modification of the boundary layer. Possible improvements of the process are discussed in terms of existent techniques for industrial electro deposition.
9:00 PM - Y3.25
Surface Morphologies and Optical Properties of Homoepitaxial ZnO by Close-Spaced Chemical Vapor Transport.
Koji Abe 1 , Tetsuya Tokuda 1 , Yuta Banno 1 , Osamu Eryu 1 Show Abstract
1 Electrical and Electronic Engineering, Nagoya Institute of Technology, Nagoya Japan
Epitaxial ZnO films on sapphire substrates are formed by various techniques such as chemical vapor deposition, laser ablation, and plasma-enhanced molecular beam epitaxy. Sapphire substrates, however, introduce a large mismatch into interfaces. Homoepitaxial ZnO films are expected to lead to better optical and electrical properties. We have studied homoepitaxial ZnO growth by close-spaced chemical vapor transport (CSCVT). It is found that surface morphologies and growth rates significantly depend on the substrate temperature. We report growth conditions which lead to flat surfaces.ZnO layers were homoepitaxially grown on O-polar (000-1) surfaces by CSCVT at the pressure of 900 Torr (Ar:CO2=5:3). ZnO powder (99.999%) was used as Zn and O sources. Zn and O species are transported to a ZnO substrate by the chemical reaction between ZnO and CO (ZnO+CO↔Zn+CO2). ZnO substrates were cleaned with organic solvents. Subsequently, a ZnO substrate and ZnO powder were placed in a carbon crucible in a vertical quartz reactor. ZnO growth was performed in the substrate temperature range from 840°C to 940°C. The source temperature was kept at 950°C. The distance between the substrate and source was set at 1.5 mm with a carbon spacer. The decomposition of ZnO powder increased the distance because the substrate was fixed on the carbon crucible. Photoluminescence (PL) measurements were carried out at 6 K by exiting the films with a He-Cd laser (325 nm).The growth rate of ZnO films decreases with increasing substrate temperature because the decomposition of ZnO substrates becomes dominant. The growth rates at 840°C and 860°C were 9 μm/h and 4 μm/h, respectively. The etching of ZnO substrates was caused at a substrate temperature of 900°C. Observation of surface morphologies shows that there are macro steps along <1-100> crystal orientations on the film grown at 840°C. The films grown at 860°C and 880°C have smooth hexagonal islands. The surface roughness decreases with increasing substrate temperature. However, flat surfaces were not obtained.To perform ZnO growth at a higher temperature, we kept the distance between the substrate and source constant (1.5 mm). The temperature of the substrate continuously increased from 920°C to 940°C during the growth. AFM observations show that keeping the distance constant improves surface morphologies. The ω rocking curves of the (0002) peak were measured to determine the crystallinity of the ZnO film. The FWHM value of the rocking curve of the ZnO film is as small as that of as-received substrates. In the PL spectrum of the ZnO film, the D0X line at 3.36 eV was clearly observed. It is found that the intensity of the broad emission related to deep levels is decreased by keeping the distance constant.
9:00 PM - Y3.26
Effect of Stress Field on Component Diffusion in Multilayer Thin Films.
Phaniraj Madakashira 1 , Vikash Sinha 1 , Om Prakash 1 Show Abstract
1 , GE India Technology Center, Bangalore India
9:00 PM - Y3.27
Solvothermal Synthesis of Copper Indium Diselenides using Alkyamines as Additives
Juyeon Chang 1 , Hye Jin Nam 1 , Geun-Tae Cho 1 , Duk-Young Jung 1 Show Abstract
1 Chemistry, SungKyunKwan Univ., Suwon, Gyeonggi-do, Korea (the Republic of)
High quality polycrystalline CuInSe2 (CIS) samples were prepared by a solvothermal process of various solvent and temperature conditions. Toluene was used as a primary solvent, and akylamines were added as catalytic additives, such as diethylamine, ethylenediamine, diethylenetriamine and triethylenetetramine. Powder X-ray diffraction of the products and its stoichiometric composition by ICP-AES support the successful syntheses of CIS. X-ray diffraction peaks indicated that synthesis of CIS required only a small quantity of akylamine, which could be optimized to increase the purity of CIS and to reduce the reaction temperature below about 110°C. The relationship between concentration of akylamine and the morphologies of the prepared CIS was studied by scanning electron microscopy.
9:00 PM - Y3.28
Cu-doped ZnSe Film with Stoichiometric Composition Deposited at Room Temperature using Compound Sources.
Masahiro Orita 1 , Takashi Narushima 1 , Hiroaki Yanagita 1 Show Abstract
1 R&D Center, HOYA Corporation, Akishima-shi, Tokyo, Japan
9:00 PM - Y3.29
The Formation of CuInSe2 Thin Film Solar Cell Absorbers from Electroplated Precursors.
Stefan Jost 1 , Frank Hergert 1 , Rainer Hock 1 , Torsten Voss 2 , Joerg Schulze 2 , Andreas Kirbs 2 , Michael Purwins 3 , Markus Schmid 3 Show Abstract
1 Chair for Crystallography and Structural Physics, University of Erlangen-Nürnberg, Erlangen Germany, 2 , Atotech Deutschland GmbH, Berlin Germany, 3 Crystal Growth Laboratory, Department of Materials Science VI, University of Erlangen-Nürnberg, Erlangen Germany
9:00 PM - Y3.3
Study of CIGS Solar Cells Back Contact.
Sylvain Marsillac 1 Show Abstract
1 Physics and Astronomy, University of Toledo, Toledo, Ohio, United States
9:00 PM - Y3.30
Characterization of CdS/CdTe Solar Cells Fabricated By Different Processes.
Tamara Potlog 1 , Khrypunov Gennadiy 2 , Kaelin Marc 3 , Zogg Hans 3 , Tiwari Ayodhya N. 2 Show Abstract
1 Physics, Moldova State University, Chisinau Moldova (the Republic of), 2 Materials for Electronic and Solar Cells, National Technical University “Kharkov Polytechnic Institute”, Kharkov Ukraine, 3 Thin Film Physics Group, Laboratory for Solid State Physics, ETH Zurich ETH Building-Technopark, Technoparkstr.1 , CH-8005 Zurich Switzerland
9:00 PM - Y3.31
Photocurrent Spectral Distribution and Relaxation in CdS/CdTe Heterojunctions
Sergiu Vatavu 1 , Iuliana Caraman 2 , Petru Gasin 1 Show Abstract
1 Physics, Moldova State University, Chisinau Moldova (the Republic of), 2 Engineering, University of Bacau, Bacau Romania
Thin film CdS/CdTe solar cells have proved their importance in use as solar energy converters achieving 16.5 % efficiency . Thin film CdS/CdTe heterojunctions have been deposited by close spaced sublimation method (CSS), onto SnO2 covered glass plates (2×2 cm2). The thickness of CdS and CdTe thin films was 0.3-1.6 μm and 2.3-6.6 μm respectively. For to enhance CdS/CdTe heterojunctions photoelectrical parameters and photosensitivity, the deposition procedure was followed by annealing in presence of CdCl2 at 420°C for 15-60 min. Ni has been used as back contact to CdTe. After annealing, the photoelectrical parameters at 1 kW/m2 are: Uoc=0.73 V, Isc=21.7 mA/cm2, ff=0.43.¶ The analysis of the photosensitivity for samples with different thicknesses of the component layers in the 78-293K temperature range showed, that the increase of the photoconductivity for photon energies hν>1.9 eV is determined by the generation-recombination processes in CdSxTe1-x interface layer, and in the 1.42 eV-1.85 eV region, by light absorption mechanism in CdTe.¶ At direct biases of the CdS/CdTe heterojunctions (2Uoc), the photocurrent spectral distribution is determined by the generation-recombination processes in CdS layer. The annealing of the heterojunction in presence of CdCl2 results in photocurrent increase more than one order of magnitude.¶ CdS/CdTe at reverse biases, having a constant sensitivity in visible and near infrared spectral region, can be used in photometry as radiation detector.¶ The analysis of the absorption spectra and the photocurrent spectral distribution at direct biases resulted in determination of the holes mean free path in CdTe layer, being equal to 1.05 μm.¶ The ratio of the ambipolar diffusion coefficient and surface recombination velocity for CdS/CdTe interface is 0.3 μm and the diffusion length is 0.6 μm at 78K. The same parameters for Ni/CdTe interface are: 0.025 μm and 0.05 μm respectively.¶ The phococurrent relaxation curves have been studied for illumination throught both sides of the heterojunctions at different biases, temperatures and wavelength, determining different penetration depths and materials excitation. Nonequilibrium charge carriers lifetime has been determined. The thermal annealing of the CdS/CdTe heterojunctions in presence of CdCl2 determine the nonequilibrium charghe carrier lifetime increase by more than one order of magnitude from 22 μs up to 280 μs.¶ X. Wu et. al. 16.5% Efficient CdS/CdTe polycrystalline thin film solar cell. 17th European Photovoltaic Solar Energy Conference, Munich, Germany, 2001, Proceedings, p.995-999.
9:00 PM - Y3.32
Alternative Route To Obtain Photovoltaic Thin Film Of CdTe.
Claudio Carvalho 1 , Rodolfo Fernandes 1 , Victor Reynoso 1 Show Abstract
1 Physics and Chemistry, Universidade Estadual Paulista - UNESP, Ilha Solteira, SP, Brazil
The demand of electrical energy is growing up quickly as result of the industrial and technological expansion. However, this expansion requires efficient, cheap and environmentally safe converting methods. Photovoltaic (PV) technologies fit perfectly in this situation. Following this motivation, a PV material synthesis research is made in the present work. We obtained CdTe thin film using polymeric precursor solution deposited on glass substrate by dip coating technique. The films were submitted to thermal treatment around 450oC during 1 hour in resistive furnace with controlled argon-carbon atmosphere. A quick study using optical microscopy showed a smooth and uniform surface before and after thermal treatment. FTIR and UV-VIS spectroscopy have shown that some compounds were eliminated after thermal treatment and the band absorption is around 650 nm, still far from the expected CdTe band, around 889 nm. The film thickness is around 3μm. Chemical composition analysis using EDX has also shown a excellent stoichiometric control. Measurement of XRD, AFM and efficiency measurements are being carried out.
9:00 PM - Y3.33
Formation of Zn-In-Se Compounds on CIGS Film by the Thermal Annealing in Dimethylzinc Stream.
Mutsumi Sugiyama 1 , Atsushi Miyama 1 , Akihisa Umezawa 1 , Toshihiro Yasuniwa 1 , Atsuki Kinoshita 1 , Hisayuki Nakanishi 1 , Shigefusa Chichibu 2 Show Abstract
1 Dept. of Electrical Engineering, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba Japan, 2 Inst. of Applied Physics, University of Tsukuba, 1-1-1 Tennodai, Tsukuba Japan
9:00 PM - Y3.34
On the Origins of Impurities in CdTe-based Thin Film Solar Cells.
Mahieddine Emziane 1 , Douglas Halliday 1 , Ken Durose 1 Show Abstract
1 Department of Physics, Durham University, Durham United Kingdom
9:00 PM - Y3.35
Formation of Cu2ZnSnS4 and Cu2ZnSnS4-CuInS2 Thin Films Investigated by In-situ Energy Dispersive X-ray Diffraction.
Alfons Weber 1 , Immo Koetschau 1 , Susan Schorr 1 , Hans-Werner Schock 1 Show Abstract
1 Solar Energy Division, Hahn-Meitner-Institut, Berlin Germany
9:00 PM - Y3.37
Electronic Structure of CuInSe2 Thin Films.
Christian Pettenkofer 1 , Carsten Lehmann 1 , Volker Eyert 2 Show Abstract
1 SE6, HMI, Berlin Germany, 2 , Universität Augsburg, Augsburg Germany
9:00 PM - Y3.4
Photosensitivity of Thin Variable-gap p-n Structures with a Triangular Profile of Energy Band Diagram.
Bogdan Sokolovskii 1 Show Abstract
1 Department of Electronics, Ivan Franko University of Lviv, Lviv Ukraine
9:00 PM - Y3.5
Structure and Microstructure of Zn2x(CuBIII)1-xX2 Semiconductors (BIII=Ga,In;X=S,Se,Te)
Susan Schorr 1 , Gerald Wagner 2 , Michael Tovar 3 , Denis Sheptyakov 4 Show Abstract
1 Solar Energy Research (SE3), Hahn-Meitner-Institute Berlin, Berlin Germany, 2 Institute of Mineralogy, Crystallography and Materials Science, University Leipzig, Leipzig Germany, 3 Structural Research (SF1), Hahn-Meitner-Institute Berlin, Berlin Germany, 4 Laboratory for neutron Scattering, ETH Zuerich&PSI Villigen, Villigen Switzerland
Solid solutions of DIIXVI and AIBIIIXVI2 compounds (D=Zn; A=Cu; B=Ga,In and X=S,SeTe) are of interest due to possible photovoltaic applications. An advantage would be a variation of the band gap from the large value of the binary wide band gap semiconductor ZnX towards the band gap of the ternary chalcopyrite type end member CuBX2. Both end members belong to the adamantine compound family, their structures are closely related but non-isotype. The tetragonal chalcopyrite structure of ternary can be derived form the cubic sphalerite type structure of the isoelectronic binaries by doubling the cubic unit cell in c-direction. The two principal noncubic features are a tetragonal deformation (1-c/2a) and displacement of the anions (u-¼ ) (u is the anion x coordinate).In this work we present the systematic investigation of structure and microstructure in 2(ZnX)x(CuBX2)1-x series by neutron and X-ray diffraction as well as transmission electron microscopy (TEM) in a compact way.Powder samples were synthesized by solid state reaction from the elements in sealed evacuated silica tubes at elevated temperatures. Neutron diffraction experiments were performed at BENSC (HMI Berlin, Germany) and the Spallation Source SINQ (PSI, Switzerland). CuKα1,2 radiation was used in X-ray powder diffraction. TEM examinations have been carried out in a Philips CM200 STEM equipped with a super twin objective lens and an EDX analysis system.The results showed the occurrence of a structural phase transition in dependence of the composition, which can be foreseen as a combination of order-disorder (cation substructure) and displacement (anion substructure) process.The 2(ZnX)-CuBIIIX2 systems form solid solution series with a miscibility gap, within two phases coexist as tetragonal domains and cubic matrix. This region was named the 2-phase field. Hence the composition dependent structural phase transition goes along with a phase separation by chemical disorder. It was revealed that within a homologeous series the 2-phase field depends on the anion, for the same anion it depends on the B(III) cation. For cubic and tetragonal mixed crystals the lattice constant depend linear on chemical composition. Moreover the anion displacement and tetragonal deformation for tetragonal mixed crystals is decreasing linearly with increasing ZnX content in CuB(III)X2. This behaviour indicates the displacement process within the anion sublattice. As an effect of the microstructure within the 2-phase field the both phases try to match in the a-b-plane, which gives rise to an increase of the tetragonal lattice constant c of the domains and an increasing tetragonal deformation. Moreover a non-random Zn distribution on the both cation sites of the chalcopyrite type structure could be deduced for tetragonal mixed crystals. With increasing ZnX content in CuB(III)X a trend to a more statistic distribution of the cations was observed, indicating the tendency of disorder in the cation substructure.
9:00 PM - Y3.6
Growth and Characterization of Erbium Doped ZnO Prepared by Vapor Phase Transport Process.
Shih-Hsuan Yang 1 , Liang Chao 1 Show Abstract
1 Electronic Engineering, National Taiwan University of Science and Technology, Taipei Taiwan
9:00 PM - Y3.7
Electronic Transport in CuIn(S,Se)2 Electrodeposited Based Solar cells, Limiting Causes for 10% Efficiencies.
Arouna Darga 1 , Veronica Bermudez 2 , Denis Mencaraglia 1 , Olivier Kerrec 2 Show Abstract
1 , LGEP- CNRS, Gif Sur Yvette France, 2 , IRDEP (CNRS-EDF), Chatou France
9:00 PM - Y3.8
Electroluminescence from Cu(In,Ga)Se2 Thin-film Solar Cells.
Thomas Kirchartz 1 , Uwe Rau 1 , Julian Mattheis 1 Show Abstract
1 Institute of Physical Electronics, University of Stuttgart, Stuttgart Germany
9:00 PM - Y3.9
Growth and Characterization of Electrodeposited CIS Absorbers.
Shalini Menezes 1 , Yan Li 1 , Subba Kodigala 1 , Sharmila Menezes 1 , Joe Rose 1 , Anura Samantilleke 2 Show Abstract
1 , InterPhases Research, Westlake Village, California, United States, 2 Department of Chemistry, University of Bath, BATH BA2 7AY United Kingdom
9:00 PM -
Y3.38 TRANSFERRED TO Y1.4