Role of substrate temperature in controlling properties of sprayed CuInS2 absorbers

Optimization of substrate temperature of spray pyrolysed CuInS2 absorber is discussed along with its effect on the photoactivity of junction fabricated. For CuInS2 thin films, properties like crystallinity, thickness and composition showed progressive behavior with substrate temperature. X-ray photoelectron spectroscopic depth profile of all the samples showed that the concentration of copper on the surface of the films is significantly lesser than that in the bulk thus avoiding need for toxic cyanide etching. Interestingly, samples prepared at 623 K had higher conductivity compared to those prepared above and below this temperature. Also, the low energy transition, in addition to the direct band gap which was observed in other samples were absent in films prepared at 623 K. From thermally stimulated conductivity studies it was seen that shallow levels present in this sample contribute to its improved conductivity. Also, CuInS2/In2S3 bilayer prepared at this substrate temperature showed higher photoactivity than those prepared at other temperatures.