1,721,222 research outputs found
CdTe thin film solar cells : present status and future perspectives
No full textThe CdTe thin film solar cells have reached enough technological maturity to be one of the most successful photovoltaic technologies in the market. From the early stage of research, in the eighties, up to now, CdTe solar cells have provided a constant increase in efficiency together with a more effective fabrication process that reduces the amount of material and increases the industrial scalability, due to the large variety of the fabrication processes and to the robustness of the material.In the last 10 years, different key issues from the recrystallization/activation treatment (enhancing CdTe grain size and passivating the grain boundaries) to the back contact stability (incapsulating copper into a stable compound) have been deeply studied and engineered. With these advances the CdTe photovoltaic technology has now the lowest cost per Watt available, due to the low amount of material involved, the low energies used in the fabrication process and the fast all-in-line production with monolithical integration of the solar cells. In this paper, recent technologies for CdTe thin film solar cell fabrication are shown, low temperature and high temperature deposition processes in the laboratory and on the industrial scale, together with the monolithical integration, together with some environmental considerations are described
Comparison of CdTe thin film photovoltaic technologies
No full textCdTe polycrystalline thin film solar cells are highly scalable devices, showing stable performance and high efficiencies. The high industrial potential of CdTe thin film solar cells has been demonstrated by the increase, in relatively short time, of the production from a few MW up to more than 200 MW per year. Highest efficiencies have been obtained by using close space sublimation (CSS) to grow CdTe. However, CdTe can be deposited with a large variety of deposition processes: in the past, some companies have successfully optimized other fabrication processes. In this paper an overview and comparison of the fabrication processes, with the different applications, will be
presented
CdTe Solar Cells
No full textCdTe photovoltaic technology is one of the most successful of the last 10 years, it is one of the first being brought into production together with amorphous silicon (already in the mid-1990s Solar Cells Inc. in the United States, Antec Solar and BP Solar in Europe were producing 60×120 cm modules) and it is now the largest in production among thin film solar cells. CdTe solar cells stand out for the robustness of the absorber material; its high chemical stability and the large variety of successful preparation methods available are the most important ones for large-area module production. In this chapter we will describe the basics of CdTe-based thin film solar cells, from the properties of the single layers, their fabrication methods, the steps that bring this device to high efficiency, and the latest improvements achieved so far
CdTe and CuInGaSe2 Thin-Film Solar Cells
No full textThin film solar cells are based on materials, which show an extraordinary high absorption coefficient so that there is no need to build thick solar cells to absorb all the light. Using this kind of materials allows one to fabricate devices with an overall thickness of less than 10 micrometers and a clear advantage in terms of material supply and fabrication energy. Thin-film solar cells offer a wide variety of choices in terms of device design, fabrication methods and substrates (flexible or rigid, metal or insulator). The deposition of different layers (contact, buffer, absorber, reflector, etc.) can be done using several techniques, which will be described later. Indeed, such versatility allows for tailoring and engineering of the layers, in order to match the solar spectrum and to improve device performance. Typically, the thin films used in these devices are polycrystalline materials, where the layer is a pattern of small crystals, whose width can range between 0.1 and 5 m. As shown in Figure 8.1, the layer is a patch of differently sized grains with different orientations. This configuration looks very disordered and irregular considering that it has to allow carriers to move through the material; however the films, when properly prepared, have the required conductivity, and devices can reach very high efficiencies up to 25%. On the other hand, the advantage of such a disordered structure is that it does not need a very precise control of crystal growth; neither does it need high energy for crystallization: this is an advantage compared to other technologies such as crystalline silicon
Thin Film Solar Cells Current Status & Future Trends
No full textThe need of more and more energy supply due to increased demand from emerging countries such as India, China and Brazil and the contemporary necessity to preserve the environment has increased the interest to the development of new technologies that make use of solar energy. In particular photovoltaic solar energy, the direct conversion of solar energy into electricity by means of semiconducting materials, had a very strong development in the last 30 years. The most important parameter that characterizes a photovoltaic device is the ratio between its conversion efficiency and its cost. A value less than 0.5 /Wp for CdTe/CdS thin film modules fabricated by “First Solar”. In any case, in order to reach the goal of 0.5 $/Wp or less, the only way is that of further developing thin film photovoltaics. In this book, the most recent results concerning thin film solar cells, covering all kinds of relevant materials, are presented by qualified experts in the field. The book is particular important for researchers who are already engaged or intend to start a research in this area. It could be also useful for the industries who want to invest their money in the new thin film photovoltaic technologies
Process for large-scale production of CdTe/CdS thin film solar cells
No full textA process for large-scale production of CdTe/CdS thin film solar cells, films of the cells being deposited, in sequence, on a transparent substrate, the sequence comprising the steps of: depositing a film of a transparent conductive oxide (TCO) on the substrate; depositing a film of CdS on the TCO film, depositing a film of CdTe on the CdS film; treating the CdTe film with CdCl2; depositing a back-contact film on the treated CdTe film. Treatment of the CdTe film with CdCl2 comprises the steps of: forming a layer of CdCl2 on the CdTe film by evaporation, while mainting the substrate at room temperature; annealing the CdTel2 layer in a vacuum chamber at a temperature generally within a range of 300 mbar and 1000 mbar in an inert gas atmosphere; removing the inert gas from the chamber so as to produce a vacuum condition, while the substrate is kept at a temperature generally within a range of 350°C and 420°C whereby any residual CdCl2 is evaporated from the CdTe film surface
Electrical Characterisation of CdTe/CdS Photovoltaic Devices
No full textThin film solar cells based on CdTe/CdS are expected to become the base material for the low-cost and efficient large-scale solar energy conversion devices. The samples have been investigate using current-voltage (I-V) and capacitance-voltage (C-V) measurements in order to define the transport mechanism in heterostructure and basic electronic parameters. Trap-assisted tunneling has been found to dominate carrier transport mechanism in the junction
Ageing of CdTe Devices by Copper Diffusion
No full textCdTe solar cells are widely used in industrial production and they currently have the lowest cost per Watt available in the market thanks to its simple and scalable technology. One of the main engineering challenges for these devices is to provide a suitable back contact for CdTe due to its high electron affinity which requires a material with a very high work function. Solar cells with copper based back contacts have shown the highest efficiencies, however it is well known that their performance reduces with time,
mainly connected with diffusion of Cu through the absorber. Working conditions (i.e. light intensity, temperature and applied bias) can dramatically affect the degradation speed. In order to study the impact of the bias on the Cu diffusion, then on performance degradation, three different kinds of stress were applied on identical CdTe solar cells with Cu/Au back contact (Dark without bias, light-temperature without bias, light temperature with bias). The degraded devices have been periodically analyzed by currentvoltage, capacitance-voltage, drive level capacitance profiling and admittance spectroscopy. A detailed analysis of defect characterization and distribution has
been addressed
Effects of activation treatment on the electrical properties of low temperature grown CdTe devices
No full textCdTe has shown a significant potential for high mass production, resulting to be one of the cheapest photovoltaic technology available. Efficiencies exceeding 17% have been obtained by the application of high temperature CdTe deposition.
However a very different role of the CdCl2 activation treatment for the low and high temperature deposited CdTe is known: requiring a strong grain size enhancement only in the first case.
In our labs, vacuum evaporated CdTe is typically treated by CdCl2-methanol saturated solution. Different amounts of this solution have been applied on CdTe layers. Final conversion efficiencies are ranging, depending on the different treatments, between 6 and 13%. The electrical properties of these finished devices have been studied by means of current-voltage, capacitance-voltage, drive level capacitance profiling and admittance spectroscopy in order to connect the electrical properties of the device with the different activation treatments.
Admittance spectroscopy shows a different defect energy distribution depending on the applied activation treatment, drive level capacitance profiling the different doping profile and the different transport mechanisms are addressed by studying the behavior of dependence of I-V characteristics with temperature
METHOD FOR THE FORMATION OF A NON-RECTIFYING BACK-CONTACT IN A CDTE /CDS THIN FILM SOLAR CELL
No full textThe present invention relates to the field of the solar cells technology and more particularly concerns a process for the large-scale production of CdTe/CdS thin film solar cells. In particular, the invention relates to an improvement to this process relating to the formation of a non-rectifying back-contact. Even if in the present specification reference is made to “CdTe/CdS thin-film” solar cells for sake of simplicity, it is to be understood that this term includes all the salt mixtures comprised in the formula
ZnxCd1-xS/CdTeyS1-y
wherein 0≦x≦0.2 and 0.9≦y≦1
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