Evaporated copper sulphide layers for all-vacuum evaporated CuxS/CdS solar cells

Abstract Copper sulphide layers have been prepared by vacuum evaporation from a single Cu x S source, as an alternative to the chemiplating technique for fabricating the upper Cu x S layer in Cu x S/CdS solar cells. Deposition rates of less that 150 A/min have been shown to produce Cu x S layers with chalcocite being the major phase. Higher deposition rates increase the copper content of the layer which dominates its optoelectrical properties. Layers free from excess copper have a chalcocite-related phase transition between 75 and 80°C, room temperature resistivity between 10 −2 and 10 −3 Ω cm and evidence of direct and indirect band gaps of 2.25 and 1.25 eV, respectively. With well controlled evaporation conditions the layers deposited on hot CdS thin film substrates are found to have highly reproducible characteristics, and are well suited for use as the absorber for the Cu x S/CdS solar cell. Open-circuit voltages up to 0.58 V have been produced in cells with efficiencies in excess of 7%.