Chemical bath deposition (CBD) generates has been successfully employed for the fabrication of II-VI semiconductor thin films. Thin film polycrystalline solar cells, such as the BP Solar 'Apollo' CdS:CdTe heterojunction device, offer the potential for low cost solar energy conversion. The large scale exploitation of these devices is partly dependent on a reduction of the potential environmental impact of the technology. The fabrication of CdS window layers by CBD at present generates considerable Cd-containing waste. Use and disposal of cadmium-containing compounds and wastes are highly regulated in the EU and elsewhere. For CdS CBD, the extent of the desired heterogeneous reaction on the substrate surface is limited by two major factors, the competing homogeneous reaction in solution and deposition of material on the CBD reactor walls. In this paper we describe our initial successful efforts to address these problems with the development of a novel high-efficiency CdS CBD system. Chemical modelling and speciation studies have enabled us to develop a process that comprises low cadmium concentrations and eliminates ammonia (which is volatile and undesirable for large scale CBD operations). Films have been characterised by spectroscopic methods (UV-vis, FL and XPS), microscopy (SEM and TEM) and powder XRD.