Download or read book High Efficiency Polycrystalline CdTe Thin Film Solar Cells with an Oxygenated Amorphous CdS a CdS O Window Layer Preprint written by and published by . This book was released on 2002 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: In the conventional CdS/CdTe device structure, the poly-CdS window layer has a bandgap of~2.4 eV, which causes absorption in the short-wavelength region. Higher short-circuit current densities (Jsc) can be achieved by reducing the CdS thickness, but this can adversely impact device open-circuit voltage (Voc) and fill factor (FF). Also, poly-CdS film has about 10% lattice mismatch related to theCdTe film, which limits the improvement of device Voc and FF. In this paper, we report a novel window material: oxygenated amorphous CdS film (a-CdS:O) prepared at room temperature by rf sputtering. The a-CdS:O film has a higher optical bandgap (2.5-3.1 eV) than the poly-CdS film and an amorphous structure. The preliminary device results have demonstrated that Jsc of the CdTe device can begreatly improved while maintaining higher Voc and FF. We have fabricated a CdTe cell demonstrating an NREL-confirmed Jsc of 25.85 mA/cm2 and a total-area efficiency of 15.4%.
Download or read book High Efficiency Polycrystalline CdTe Thin Film Solar Cells with an Oxygenated Amorphous CdS a CdS written by and published by . This book was released on 2002 with total page 7 pages. Available in PDF, EPUB and Kindle. Book excerpt: In the conventional CdS/CdTe device structure, the poly-CdS window layer has a bandgap of (almost equal to)2.4 eV, which causes absorption in the short-wavelength region. Higher short-circuit current densities (Jsc) can be achieved by reducing the CdS thickness, but this can adversely impact device open-circuit voltage (Voc) and fill factor (FF). Also, poly-CdS film has about 10% lattice mismatch related to the CdTe film, which limits the improvement of device Voc and FF. In this paper, we report a novel window material: oxygenated amorphous CdS film (a-CdS:O) prepared at room temperature by rf sputtering. The a-CdS:O film has a higher optical bandgap (2.5-3.1 eV) than the poly-CdS film and an amorphous structure. The preliminary device results have demonstrated that Jsc of the CdTe device can be greatly improved while maintaining higher Voc and FF. We have fabricated a CdTe cell demonstrating an NREL-confirmed Jsc of 25.85 mA/cm2 and a total-area efficiency of 15.4%.
Download or read book High Efficiency Ultra Thin Cadmium Telluride CdTe Solar Cells written by Nowshad Amin and published by LAP Lambert Academic Publishing. This book was released on 2013 with total page 148 pages. Available in PDF, EPUB and Kindle. Book excerpt: Thin film cadmium telluride absorbers with cadmium sulphide hetero-junction partner are promising candidates for high efficiency low cost solutions of solar energy harvesting devices. These devices have band gaps well-suited for effective absorption of sunlight. Most importantly, the materials used in these devices can be deposited in a variety of industry-friendly ways, so that the cost associated with manufacturing is generally lower than other available technologies. Although poly-crystalline CdS has been found to be the best suited heterojunction partner for CdTe solar cell, the conventional polycrystalline CdS/CdTe cell has few issues that limit device performance. In order to overcome these problems, this study proposes the introduction of poly-CdS to amorphous oxygenated CdS (a-CdS: O) as window layer. The a-CdS: O window material has higher optical band gap (2.5-3.1 eV), better lattice match with CdTe absorber materials and reduced inter-diffusion tendency of CdS and CdTe layers. This book systematically demonstrates the conversion process of poly CdS to a-CdS: O and develops a strategy for the fabrication of suitable a-CdS: O layer to be applied in CdTe solar ce
Download or read book CdS CdTe Thin film Solar Cell with a Zinc Stannate Buffer Layer written by Xuanzhi Wu and published by . This book was released on 1998 with total page 5 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book High efficiency Cadmium and Zinc telluride based Thin film Solar Cells written by and published by . This book was released on 1992 with total page 82 pages. Available in PDF, EPUB and Kindle. Book excerpt: This report describes research into polycrystalline CdTe solar cells grown by metal-organic chemical vapor deposition. Efficiencies of (approximately)10% were achieved using both p-i-n and p-n structures. A pre-heat treatment of CdS/SnO2/glass substrates at 450°C in hydrogen atmosphere prior to the CdTe growth was found to be essential for high performance because this heat treatment reduces oxygen-related defects from the CdS surface. However, this treatment also resulted in a Cd-deficient CdS surface, which may in part limit the CdTe cell efficiency to 10% due to Cd vacancy-related interface defects. Preliminary model calculations suggest that removing these states can increase the cell efficiency from 10% to 13.5%. Photon absorption in the CdS film also limits the cell performance, and eliminating this loss mechanism can result in CdTe efficiencies in excess of 18%. Polycrystalline, 1.7-e, CdZnTe films were also grown for tandem-cell applications. CdZnTe/CdS cells processed using the standard CdTe cell fabrication procedure resulted in 4.4% efficiency, high series resistance, and a band-gap shift to 1.55 eV. The formation of Zn-O at and near the CdZnTe surface is the source of high contact resistance. A saturated dichromate each prior to contact deposition was found to solve the contact resistance problem. The CdCl2 treatment was identified as the cause of the observed band-gap shift due to the preferred formation of ZnCl2. 59 refs.
Download or read book High efficiency CTO ZTO CdS CdTe Polycrystalline Thin film Solar Cells written by and published by . This book was released on 2001 with total page 4 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Cds cdte Thin Film Solar Cells with Zinc Stannate Buffer Layer written by Srilatha Bapanapalli and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: ABSTRACT: CdS/CdTe solar cell performance and reproducibility can be improved by integrating a ZTO buffer layer, which interdiffuses into the CdS layer during device fabrication. Reducing the thickness of CdS layer improves the QE in the blue spectral region without affecting the device performance. This buffer layer is expected to prevent the formation of localized TCO/CdTe junction during high temperature processing. The CdS/CdTe Solar Cell was modified by introducing ZTO as a buffer layer between the window layer (CdS) and the absorber layer (CdTe). Studies were performed on different varying ZTO processing parameters like (a) Zn/Sn atomic ratios during sputtering process, (b) ZTO thickness, (c) ZTO heat treatment temperature, and (d) ZTO heat treatment ambient.
Download or read book High Efficiency Thin Film CdTe and A Si Based Solar Cells written by and published by . This book was released on 2000 with total page 5 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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(subscript x)Te{sub 1-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(subscript x)Te{sub 1-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 x 10−5 torr) was beneficial for growing high-quality films from ITO targets.
Download or read book Development of High efficiency Thin film CdTe Solar Cells Final Subcontract Report 1 February 1992 30 November 1995 written by and published by . This book was released on 1996 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: This report describes work performed by the Georgia Institute of Technology (GIT) to bring the polycrystalline CdTe cell efficiency a step closer to the practically achievable efficiency of 18% through fundamental understanding of detects and loss mechanisms, the role of chemical and heat treatments, and investigation of now process techniques. The objective was addressed by a combination of in-depth characterization, modeling, materials growth, device fabrication, and 'transport analyses of Au/Cu/CdTe/CdS/SnO 2 glass front-wall heterojunction solar cells. GiT attempted to understand the loss mechanism(s) in each layer and interface by a step-by-step investigation of this multilayer cell structure. The first step was to understand, quantify, and reduce the reflectance and photocurrent loss in polycrystalline CdTe solar calls. The second step involved the investigation of detects and loss mechanisms associated with the CdTe layer and the CdTe/CdS interface. The third stop was to investigate the effect of chemical and heat treatments on CdTe films and cells. The fourth step was to achieve a better and reliable contact to CdTe solar cells by improving the fundamental understanding. Of the effects of Cu on cell efficiency. Finally, the research involved the investigation of the effect of crystallinity and grain boundaries on Cu incorporation in the CdTe films, including the fabrication of CdTe solar calls with larger CdTe grain size.
Download or read book Approaches to Fabricating High efficiency Ultra thin CdTe Solar Cells written by Wei Xia and published by . This book was released on 2012 with total page 173 pages. Available in PDF, EPUB and Kindle. Book excerpt: "This thesis is an investigation of the fabrication, characterization and performance of high-efficiency and ultra-thin CdTe solar cells with an aim of reducing the material usage and cell manufacturing cost. Several approaches have been successfully carried out to directly or indirectly improve the device performance. Major achievements are listed below: 1) A close-spaced sublimation (CSS) process with an improved control of the deposition temperature-time profile was developed to fabricate high-quality ultra-thin CdTe films. Three key factors in the CSS process including oxygen pressure, substrate temperature and thermal etch duration were optimized. 2) A two-stage post-deposition treatment including a high temperature annealing (HTA) followed by a vaporous cadmium chloride treatment (VCC) was developed and optimized for the growth of high-quality CdTe films. The effects of HTA and VCC on ultra-thin CdTe solar cells were revealed by a combination of characterization techniques, including photoluminescence. 3) In a collaborative effort two new back contact buffers, MoOx and Te/Cu, were identified and applied in ultra-thin CdTe solar cells. Substitution of a conventional acid etching method with the new back contact buffers was found to enhance the cell efficiency from ~10% to ~13.5%. Moreover, the new buffers improved the reproducibility of cell fabrication. A low-resistance electrical back contact based on the Te/Cu buffer and Ni as electrode was developed. A thermal activation process was found necessary to promote ohmic contact formation. Cu diffusion into the Te layer and CdTe bulk layer occurred during the thermal activation process and must be controlled to prevent excessive diffusion into the CdS/CdTe junction. The effects of Cu concentration and Te thickness on device performance and cell stability were systematically investigated and a cell efficiency as high as ~15% with good stability has been achieved using an optimized Te/Cu buffer. 4) A novel vaporous zinc chloride treatment was developed for the formation of Cd1xZnxS from CdS films. Compared with conventional fabrication methods, the VZC method features simple setup and operation and is capable of producing Cd1xZnxS films with a homogenous structure. The Zn to Cd doping ratio in Cd1−xZnxS can be easily controlled by adjusting the process parameters. By replacing CdS with a more transparent Cd1−xZnxS as the window layer, CdTe solar cells with a higher (12-14%) short-circuit current, Jsc, have been demonstrated"--Page v-vi.
Download or read book Development of High Efficiency Polycrystalline Cadmium Telluride Cadmium Sulfide Solar Cells Using Electrodeposition written by Wenjie Song and published by . This book was released on 1999 with total page 258 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Development of Back Contacts for CdTe Thin Films Solar Cells written by Fadhil Khalaf Dahash Alfadhili and published by . This book was released on 2020 with total page 100 pages. Available in PDF, EPUB and Kindle. Book excerpt: Thin film solar cells based on polycrystalline p-type cadmium telluride (CdTe) represent one of these the most promising photovoltaic (PV) device due to high efficiency and low-cost production. Currently, CdTe solar cells provide the lowest cost electricity generation in utility-scale applications, which is a cost-competitive with the traditional power source, fossil fuel. CdTe thin film PV has attained 22.1 % of power conversion efficiency for small area scale and 18.6 % for modules scale. However, the high efficiency of CdTe devices has been achieved by increasing the photo-generated current by changing the traditional window layer (CdS) of CdTe to a wider bandgap material with better band alignment. The open-circuit voltage (VOC) remains below the theoretical limit due to a barrier at the back of the device due to the deep valence band edge of CdTe (-5.9 eV). Voc can be increased by adding a buffer layer between CdTe and the back electrode to decrease band banding and reducing carrier recombination at the back interface. In this thesis, several materials were investigated as a back-buffer layer, such as single-wall carbon nanotube (SWCNT), zinc telluride (ZnTe), tellurium (Te), and cadmium zinc telluride (CZT) to minimize the bend bending at CdTe/back-buffer layer interface. An alternative method to reduce the carrier recombination at the rear surface, the use of aluminum oxide (Al2O3) layer as a passivation layer was also demonstrated. Finally, an effective method of CdCl2 treatment for CZT thin film was investigated. This method shows that zinc (Zn) can be maintained during the heat treatment.
Download or read book CdTe CdS Thin Film Solar Cells Fabricated on Flexible Substrates written by Vasilios Palekis and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Cadmium Telluride (CdTe) is a leading thin film photovoltaic (PV) material due to its near ideal bandgap of 1.45 eV and its high optical absorption coefficient. The typical CdTe thin film solar cell is of the superstrate configuration where a window layer (CdS), the absorber (CdTe) and a back contact are deposited onto glass coated with a transparent electrode. Substrate CdTe solar cells where the above listed films are deposited in reverse are not common. In this study substrate CdTe solar cells are fabricated on flexible foils. The properties of the Molybdenum back contact, Zinc Telluride (ZnTe) interlayer and CdTe absorber on the flexible foils were studied and characterized using X-Ray Diffraction (XRD), and Scanning Electron Microscopy (SEM). Substrate curvature and film flaking was observed during the fabrication as a result of differences in thermal expansion coefficients between the substrate and the deposited films, and also due to impurity diffusion from the foil into the film stack. In order to overcome this problem diffusion barriers where used to eliminate contamination. Silicon dioxide (SiO2), silicon nitride (Si3N4) and molybdenum nitride (MoxNy) were used as such barriers. Electrical characterization of completed devices was carried out by Current-Voltage (J-V), Capacitance-Voltage (C-V) and Spectral Response (SR) measurements. Roll-over was observed in the first quadrant of J-V curves indicating the existence of a back barrier due to a Schottky back contact. The formation of non-rectifying contact to p-CdTe thin-film is one of the major and critical challenges associated with the fabrication of efficient and stable solar cells. Several materials (ZnTe, Cu, Cu2Te, and Te) were studied as potential candidates for the formation of an effective back contact.
Download or read book Thin Film Solar Cells written by K. L. Chopra and published by Springer Science & Business Media. This book was released on 2013-11-11 with total page 615 pages. Available in PDF, EPUB and Kindle. Book excerpt: "You, 0 Sun, are the eye of the world You are the soul of all embodied beings You are the source of all creatures You are the discipline of all engaged in work" - Translated from Mahabharata 3rd Century BC Today, energy is the lifeline and status symbol of "civilized" societies. All nations have therefore embarked upon Research and Development pro grams of varying magnitudes to explore and effectively utilize renewable sources of energy. Albeit a low-grade energy with large temporal and spatial variations, solar energy is abundant, cheap, clean, and renewable, and thus presents a very attractive alternative source. The direct conver sion of solar energy to electricity (photovoltaic effect) via devices called solar cells has already become an established frontier area of science and technology. Born out of necessity for remote area applications, the first commercially manufactured solar cells - single-crystal silicon and thin film CdS/Cu2S - were available well over 20 years ago. Indeed, all space vehicles today are powered by silicon solar cells. But large-scale terrestrial applications of solar cells still await major breakthroughs in terms of discovering new and radical concepts in solar cell device structures, utilizing relatively more abundant, cheap, and even exotic materials, and inventing simpler and less energy intensive fabrication processes. No doubt, this extraordinary challenge in R/D has led to a virtual explosion of activities in the field of photovoltaics in the last several years.
Download or read book High Efficiency Thin Film CdTe and A Si Based Solar Cells written by and published by . This book was released on 2001 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: This report describes the research on high-efficiency CdTe-based thin-film solar cells and on high-efficiency a-Si-based thin-film solar cells. Implemented a diode-array spectrograph system and used optical emission spectroscopy to help optimize the reactive sputtering of N-doped ZnTe for CdTe back-contact structures. Identified the photoluminescence signatures of various defect states in CdTe related to Cd vacancies, CuCd acceptors, Cu-VCd complexes, and donor-acceptor pairs, and related these states to instabilities in the hole concentration at room temperature. Showed that Cu is an important non-radiative center in CdS, reducing the PL efficiency. Studied band tailing in CdS weakly alloyed with CdTe and CdTe weakly alloyed with CdS. Fabricated superstrate ITO/CdS/CdTe cells on Mo substrates with efficiencies above 7.5%. Collaborated in studies of EXAFS of Cu in CdTe which indicate a Cu-Te bond length of 2.62 Å or 6.7% shorter than the CdTe, bond in agreement with calculations of Wei et al. Provided assistance to two groups on laser scribing. Comparatively studied the performance of a-SiGe solar cells and properties of a-SiGe single-layer films deposited using a wide range of H dilution, observed transition from a-SiGe to [mu]c-SiGe at high H dilution and the impact on cell performances. Comparatively studied the performance of a-SiGe solar cells and properties of a-SiGe single-layer films with different Ge contents, suitable for use as component cells of triple-junction devices. Fabricated a-Si-based solar cells on ultra-thin stainless-steel substrate (7.5 micron) and obtained equivalent performance and yield as on the regular SS substrates (127 microns). Comparatively studied the performance of a-Si-based solar cells on SS substrates and on SnO2-coated glass substrates. Studied the performance of p-layers deposited under various deposition conditions for n-i-p type solar cells. Performed an analysis for the component cell current-matching within a triple-junction solar cell.
Download or read book CdS CdTe Solar Cells Containing Directly Deposited CdSxTe1 x Alloy Layers written by and published by . This book was released on 2011 with total page 6 pages. Available in PDF, EPUB and Kindle. Book excerpt: A CdSxTe1-x layer forms by interdiffusion of CdS and CdTe during the fabrication of thin-film CdTe photovoltaic (PV) devices. The CdSxTe1-x layer is thought to be important because it relieves strain at the CdS/CdTe interface that would otherwise exist due to the 10% lattice mismatch between these two materials. Our previous work [1] has indicated that the electrical junction is located in this interdiffused CdSxTe1-x region. Further understanding, however, is essential to predict the role of this CdSxTe1-x layer in the operation of CdS/CdTe devices. In this study, CdSxTe1-x alloy films were deposited by radio-frequency (RF) magnetron sputtering and co-evaporation from CdTe and CdS sources. Both RF-magnetron-sputtered and co-evaporated CdSxTe1-x films of lower S content (x
Download or read book High Efficiency Cadmium Telluride and Zinc Telluride Based Thin film Solar Cells written by and published by . This book was released on 1992 with total page 108 pages. Available in PDF, EPUB and Kindle. Book excerpt: This report describes work to improve the basic understanding of CdTe and ZnTe alloys by growing and characterizing these films along with cell fabrication. The major objective was to develop wide-band-gap (1.6--1.8 eV) material for the top cell, along with compatible window material and transparent ohmic contacts, so that a cascade cell design can be optimized. Front-wall solar cells were fabricated with a glass/SnO2/CdS window, where the CdS film is thin to maximize transmission and current. Wide-band-gap absorber films (E{sub g} = 1.75 eV) were grown by molecular beam epitaxy (MBE) and metal-organic chemical vapor deposition (MOCVD) techniques, which provided excellent control for tailoring the film composition and properties. CdZnTe films were grown by both MBE and MOCVD. All the as-grown films were characterized by several techniques (surface photovoltage spectroscopy, Auger electron spectroscopy (AES), and x-ray photoelectron spectroscopy (XPS)) for composition, bulk uniformity, thickness, and film and interface quality. Front-wall-type solar cells were fabricated in collaboration with Ametek Materials Research Laboratory using CdTe and CdZnTe polycrystalline absorber films. The effects of processing on ternary film were studied by AES and XPS coupled with capacitance voltage and current voltage measurements as a function of temperature. Bias-dependent spectral response and electrical measurements were used to test some models in order to identify and quantify dominant loss mechanisms.
