Study of thin film poly-crystalline CdTe solar cells presenting high acceptor concentrations achieved by in-situ arsenic doping

Doping of CdTe using Group-V elements (As, P, and Sb) has gained interest in pursuit of increasing the cell voltage of CdTe thin film solar devices. Studies on bulk CdTe crystals have shown that much higher acceptor concentration than the traditional copper treatment is possible with As, P or Sb, enabled by high process temperature and/or rapid thermal quenching under Cd overpressure. We report a comprehensive study on in-situ As doping of poly-crystalline CdTe solar cells by MOCVD, whereby high acceptor densities, approaching 3 × 1016 cm−3 were achieved at low growth temperature of 390 °C. No As segregation could be detected at grain boundaries, even for 1019 As cm−3. A shallow acceptor level (+0.1 eV) due to AsTe substitutional doping and deep-level defects were observed at elevated As concentrations. Devices with variable As doping were analysed. Narrowing of the depletion layer, enhancement of bulk recombination, and reduction in device current and red response, albeit a small near infrared gain due to optical gap reduction, were observed at high concentrations. Device modelling indicated that the properties of the n-type window layer and associated interfacial recombination velocity are highly critical when the absorber doping is relatively high, demonstrating a route for obtaining high cell voltage

Functional materials for sustainable energy applications

Global demand for low cost, efficient and sustainable energy production is ever increasing. Driven by recent discoveries and innovation in the science and technology of materials, applications based on functional materials are becoming increasingly important. Functional materials for sustainable energy applications provides an essential guide to the development and application of these materials in sustainable energy production. Part one reviews functional materials for solar power, including silicon-based, thin-film, and dye sensitized photovoltaic solar cells, thermophotovoltaic device modelling and photoelectrochemical cells. Part two focuses on functional materials for hydrogen production and storage. Functional materials for fuel cells are then explored in part three where developments in membranes, catalysts and membrane electrode assemblies for polymer electrolyte and direct methanol fuel cells are discussed, alongside electrolytes and ion conductors, novel cathodes, anodes, thin films and proton conductors for solid oxide fuel cells. Part four considers functional materials for demand reduction and energy storage, before the book concludes in part five with an investigation into computer simulation studies of functional materials. With its distinguished editors and international team of expert contributors, Functional materials for sustainable energy applications is an indispensable tool for anyone involved in the research, development, manufacture and application of materials for sustainable energy production, including materials engineers, scientists and academics in the rapidly developing, interdisciplinary field of sustainable energy. © 2012 Woodhead Publishing Limited All rights reserved

A Comparison of Studies Conducted in Wales and Ireland on Issues Affecting Uptake of Micro-Generation Training

In 2007 Irvine and Stafford [1] surveyed the attitude to the need for enhanced renewable education within groups of Electricians, Architects and Chemists in Wales. Similar groups were surveyed in Ireland in 2008. In comparing the attitudes of students in these two countries the principal differences are governmental support for microgeneration, the quantity of installed microgeneration and the year of the survey. The two countries are broadly similar in terms of geography, climate, population size, ethnicity, broadcast media, educational achievements, economy and income spread. In Ireland there is greater support for governmental intervention and for increased levels of installation. This could be a reaction to the very low level of activity that prevails in Ireland. The rapid changes during 2008 in economic outlook and in Climate Change consensus may have impacted on the responses. In many areas addressed in the survey the disciplines adopted a consensus position that superseded the national differences

The role of controlled nucleation in the growth of CdS thin films on ITO/glass for solar cells

The MOCVD growth of cadmium sulphide from dimethyl cadmium and ditertiarybutyl sulphide on indium tin oxide (ITO) coated glass is optimized in this work. Optimum transmission characteristics and grain size are observed for films grown at 290 degrees C at VI/II ratios of 1-1.5. This was related to the identification of a nucleation delay during in situ growth monitoring via laser interferometry. The nucleation delay is noted to vary with temperature and also VI/II ratio, allowing the rationalization of the resulting film quality in terms of this observation. Structural analysis indicates polycrystalline CdS of hexagonal phase of (1 0 0) preferred orientation. (C) 1998 Kluwer Academic Publishers.</p

Effects of Cd1-xZnxS alloy composition and post-deposition air anneal on ultra-thin CdTe solar cells produced by MOCVD

Ultra-thin CdTe:As/Cd1-xZnxS photovoltaic solar cells with an absorber thickness of 0.5 µm were deposited by metal-organic chemical vapour deposition on indium tin oxide coated boro-aluminosilicate substrates. The Zn precursor concentration was varied to compensate for Zn leaching effects after CdCl2 activation treatment. Analysis of the solar cell composition and structure by X-ray photoelectron spectroscopy depth profiling and X-ray diffraction showed that higher concentrations of Zn in the Cd1-xZnxS window layer resulted in suppression of S diffusion across the CdTe/Cd1-xZnxS interface after CdCl2 activation treatment. Excessive Zn content in the Cd1-xZnxS alloy preserved the spectral response in the blue region of the solar spectrum, but increased series resistance for the solar cells. A modest increase in the Zn content of the Cd1-xZnxS alloy together with a post-deposition air anneal resulted in an improved blue response and an enhanced open circuit voltage and fill factor. This device yielded a mean efficiency of 8.3% over 8 cells (0.25 cm2 cell area) and best cell efficiency of 8.8%