CdS/Cu2S solar cells by the chemical spray deposition-ion exchange process

A novel process has been developed for the fabrication of thin films of CdS. As the initial step, films of CdO which are 1-3 microns thick are deposited by spray pyrolysis of a cadmium salt onto substrates of SnO2-coated glass. These films are then subjected to an ion exchange procedure in a flowing sulfide ambient at temperatures of 400-500 C. The films are completely converted into CdS. The CdS films, now 2-6 microns thick, have grain sizes of 1-3 microns. The material exhibits green photoluminescence, and the collection efficiency of carriers generated in the CdS approaches 80%. Problems have been encountered in the fabrication of high quality CdS/Cu2S heterojunction solar cells due to the inability to form good junctions. The photocurrents were seriously limited by recombination in the junction, and respectible values were only achieved under conditions of reverse bias.