Novel approach to the chemical bath deposition of chalcogenide semiconductors

Chemical bath deposition (CBD) generates has been successfully employed for the fabrication of II-VI semiconductor thin films. Thin film polycrystalli ne solar cells, such as the BP Solar 'Apollo' CdS:CdTe heterojunction devic e, offer the potential for low cost solar energy conversion. The large scal e exploitation of these devices is partly dependent on a reduction of the p otential environmental impact of the technology. The fabrication of CdS win dow layers by CBD at present generates considerable Cd-containing waste. Us e and disposal of cadmium-containing compounds and wastes are highly regula ted in the EU and elsewhere. For CdS CBD, the extent of the desired heterog eneous reaction on the substrate surface is limited by two major factors, t he competing homogeneous reaction in solution and deposition of material on the CBD reactor walls. In this paper we describe our initial successful ef forts to address these problems with the development of a novel high-effici ency CdS CBD system. Chemical modelling and speciation studies have enabled us to develop a process that comprises low cadmium concentrations and elim inates ammonia (which is volatile and undesirable for large scale CBD opera tions). Films have been characterised by spectroscopic methods (UV-vis, FL and XPS), microscopy (SEM and TEM) and powder XRD. (C) 2000 Elsevier Scienc e S.A. All rights reserved.