THIN-FILM II-VI PHOTOVOLTAICS

With the exception of HgSe and HgTe, II-VI compounds are direct gap semiconductors with sharp optical absorption edge and large absorption coefficients at above bandgap wavelengths. Device quality polycrystalline films of II-VI compounds can be prepared from inexpensive raw materials by a number of low-cost methods. They are well-suited for thin film solar cells and provide an economically viable approach to the terrestrial utilization of solar energy. Thin him II-VI solar cells are usually of the heterojunction type consisting of a high bandgap window (or collector) and a lower bandgap absorber. The grain boundary effects in polycrystalline II-VI films are considerably less pronounced than those in III-V films and can be passivated, at least partially, by chemical treatment. The use of CdS, ZnO, ZnSe and Cd1-xZnxS as the window and the use of CdTe and Cd1-xZnxTe as the absorber are reviewed in this paper. The fabrication and characteristics of a number of the thin film solar cell structures are discussed with emphasis on the thin film CdS/CdTe solar cell.