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[en] Cadmium telluride-based solar cell is the most successfully commercialised thin film solar cell today. The laboratory-scale small devices have achieved ~ 22%, and commercial solar panels have reached ~ 18% conversion efficiencies. However, there are various technical complications and some notable scientific contradictions that appear in the scientific literature published since the early 1970s. This review paper discusses some of these major complications and controversies in order to focus future research on issues of material growth and characterisation, post-growth processing, device architectures and interpretation of the results. Although CdTe can be grown using more than 14 different growth techniques, successful commercialisation has been taken place using close-space sublimation and electrodeposition techniques only. The experimental results presented in this review are mainly based on electrodeposition. Historical trends of research and commercial successes have also been discussed compared to the timeline of novel breakthroughs in this field. Deeper understanding of these issues may lead to further increase in conversion efficiencies of this solar cell. Some novel ideas for further development of thin film solar cells are also discussed towards the end of this paper.
[en] Cu2ZnSn(S, Se)4 (CZTSSe) is a promising alternative absorber material to achieve high power conversion efficiencies, besides its property of involving low-cost and earth-abundant elements when compared to Cu(In, Ga)Se2 (CIGS) and cadmium telluride (CdTe), to be used in solar cell technology. In this study, a novel fabrication technique was developed by utilizing RF sputtering deposition of CZTSSe thin films having a surface decorated with self-assembled nanoflakes. The formation of nanoflakes was investigated by detailed spectroscopic method of analysis in the effect of each stacked layer deposition in an optimized sequence and the size of nanoflakes by an accurate control of sputtering process including film thickness. Moreover, the effects of substrate temperature on the formation of nanoflakes on the film surface were discussed at a fixed deposition route. One of the main advantages arising from the film surface with self-assembled nanoflakes is the efficient light trapping which decreases the surface reflectance. As a result of the detailed production and characterization studies, it was observed that there was a possibility of repeatable and controllable fabrication sequence for the preparation of CZTSSe thin films with self-textured surfaces yielding low surface reflectance. (paper)
[en] With the increasing consumption of conventional energy and the gradually serious environmental crisis, the research and application of solar cells attracted a worldwide attention. In the past decades, the progress of the thin 40 film preparation technology promoted the technology of the second generation solar cells based on semiconductor thin film materials to flourish. Due to the demand for less material, the thin film solar cell technology can effectively reduce the cost of materials. Moreover, the thin film materials can flexibly deposit on substrates such as glass, stainless steel, and plastic, especially suitable for solar building integration
[en] The environmental effects of the production and recycling of different types of solar cells are evaluated on the basis of life-cycle cost analyses. The life cycle analyses takes account of the production and purification of silicon, the production of crystalline and amorphous silicon modules as well as the production of cadmium telluride/CIS modules. The potential environmental effects of silicon solar cells are relatively small and are mainly linked with the emission of greenhouse gases and acidified substances during the production stage. For the cadmium telluride solar cells however, several potential problems need to be clarified before these cells are produced on a large scale. In particular, potential bottlenecks are associated with the combustion of a small fraction of modules that are not recycled. In addition, the expected emission of cadmium and selenium may be ten times larger than the emissions for modern coal based power plants in a the worst case scenario. Finally, the present knowledge on the recycling processes for cadmium telluride modules is insufficient. (A.S.)
[en] Based on the n-CdS/p-CdTe heterojunction solar cell to thin films, both polycrystalline materials, started to be studied at beginning of the 1970s. However, since the 1960s were structures in which the active material was CdTe. Since then, in almost all proposed cell designs, the main problems encountered related to two important points: recombination losses associated with the main interface and the difficulty to obtain a low resistance ohmic contact with the p-CdTe. For decades, the efficiency of the cell was to rise as I studied and perfected the same from a macroscopic view of the device. Slowly they proposed, manufactured and studied structures responding with higher conversion efficiency. However, in recent years emphasis has been on the need to understand the microscopic mechanisms responsible for the transformations that occur in the device during the manufacturing process of the same. This fact has caused a deepening in the study of polycrystalline nature of the materials making up the cell, using techniques for solving micro and Nano. Special attention have been the borders of grain in the CdTe and studies related to the main junction between CdTe and CdS. This article will attempt to reflect an analysis of the evolution in the design of this type of cell, from its beginnings up to our times.
[en] A variety of issues face the photovoltaic (PV) industry in order to meet a market penetration goal of more than gigawatt per year in worldwide sales before the year 2020. Although the PV market is dominated by silicon-based technology, it is not reasonable to project installed system prices of below $1.50/W in the next 5 or even 20 years without including the impact of polycrystalline thin films. Polycrystalline thin-film technologies, including cadmium telluride (CdTe)-based technologies, are a viable option for enabling lower costs, more rapid market expansion, and gigawatt/yr annual sales. A number of issues must be resolved in order to demonstrate a competitive price of energy to the customer in the range of the $0.11-0.16/kWh. (Author)
[en] This work concerns the preparation and characterisation of n-CdS/p-CdTe thin film solar cells using a close space sublimation system (CSS) to deposit the p-CdTe layer. The effects of preparation conditions of CdTe on growth rate and the texture of the film were investigated. The cells were characterised by measurements of I-V, C-V, spectral response, photocapacitance and electroluminescence. The growth rate of CdTe increased as the source temperature increased with an activation energy ∼ 1.9 eV, whereas it was constant and independent of the substrate temperature, up to some breakpoint temperature, above which the rate decreased rapidly to zero. Increasing the pressure during growth allows growth to take place at higher temperatures but at the expense of growth rate. The growth rate increased as the separation between the source and the substrate decreased. The CdTe films grown at 335 deg. C substrate temperature showed a highly preferred (111) orientation and small grain size, whereas the films deposited at higher temperature showed a progressive loss of (111) orientation and an increase in grain size. The CdCl2 treatment for the CdTe layer increased the efficiency of the solar cells from about 3% to around 10%. The I-V dark characteristics suggest that the CdCl2 treatment changed the current transport mechanism across the junction from emission/recombination with activation energy around 0.07eV to a tunnelling mechanism. Solar cells fabricated with SnO2 give higher efficiencies than cells fabricated with ITO due to the interface between the ITO and CdS layer, which becomes rectifying after heating at 400 deg. C in air. There are many preparation parameters which affect the interdiffusion between the CdTe and CdS layer, and so modify the spectral response. In the present study, the effects of the CdCl2 treatment of CdTe and CdS layers, the thickness of CdCl2 and the time of annealing, the thickness of the CdS layer and the substrate temperature were investigated in terms of the spectral response. These studies tended to confirm that interdiffusion had taken place, with significant effects on the spectral response. The photocapacitance measurements indicated the existence of some levels below the conduction band at 0.4, 0.2 eV in p-CdTe and at 0.55eV in n-CdS, also some deep levels above the valance band at 0.24, 0.1 eV in p-CdTe and 0.71 eV in n-CdS. (author)
[en] Cadmium telluride solar cells for power generation may give rise to environmental pollution with cadmium in the event of incidents during fabrication, fires during operation or inappropriate disposal after use. Fires may liberate more than 50% of cadmium contained; disposal at municipal landfills and sufficient contact with water may even release 100% of cadmium. According to the waste disposal regulations in force, cadmium telluride cells, because of their cadmium content and the high risk of cadmium liberation on contact with water, must be disposed of in underground storages of category six. (orig.)
[de]Die Stromerzeugung mit Hilfe von cadmiumhaltigen Solarzellen kann bei Produkten der Zellen, Braenden waehrend des Betriebs und unsachgerechter Entsorgung zu Cadmiumbelastungen der Umwelt fuehren. Bei Braenden koennen ueber 50% des Cadmiuminventars freigesetzt werden, bei Deponierung in einer Hausmuelldeponie und ausreichendem Wasserkontakt sogar 100% des Cadmiuminventars. Nach geltenden Muellbestimmungen muessen Cadmium-Tellurid-Zellen aufgrund ihres Cadmium-Gehalts und dem hohen Freisetzungsrisiko vom Cadmium bei Wasserkontakt in unterirdischen Deponien der Deponieklasse 6 entsorgt werden. (orig.)
[en] Temperature and doping-level dependence of CdTe solar cells is investigated, taking into account the involvement of excitons on photocurrent transport. We show that the density of excitons in CdTe is comparable with that of minority carriers at doping levels ≥1015 cm-3. From the investigation of the dark-saturation current, we show that the product of electron and hole concentrations at equilibrium is several orders of magnitude more than the square of the intrinsic carrier concentration. With this assumption, we have studied the effect of excitons on CdTe solar cells, and the effect is negative. CdTe solar cell performance with excitons included agrees well with existing experimental results. (c) 2000 American Institute of Physics