Growth of polycrystalline CdS and CdTe thin layers for high efficiency thin film solar cells

Recently, conversion efficiencies close to 16% for thin film solar cells ba sed on the CdS/CdTe heterojunction have been reported. These relevant resul ts, however, have not yet solved the problems which arise when industrial p roduction is undertaken as the demand for low cost imposes constraints whic h considerably limit the final efficiency of the cells. In this paper, we w ill show that very high conversion efficiencies can still be achieved even making use of low cost soda-lime glass as substrate. In fact, the Na contai ned in this kind of glass diffuses during the fabrication of the cell into the active layers of the device causing a substantial decrease of the fill factor and consequently of the efficiency of the cell. In particular, we wi ll describe the methods and the magnetron sputtering techniques used to gro w a polycrystalline CdS thin film with a controlled Na content. We will als o describe the details of the growth via the close-spaced sublimation (CSS) technique of the CdTe polycrystalline film, which are crucial for the hete rojunction and the back contact which has been fabricated exploiting the ch aracteristics of Sb2Te3 which is a low gap p-type semiconductor with a high conductivity. (C) 2000 Elsevier Science S.A. All rights reserved.