Studies in CuInS2 based solar cells, including ZnS and In2S3 buffer layers

The influence of the growth conditions on the surface chemistry and on the homogeneity of the chemical composition of CuInS2 (CIS) thin films, prepared by sequential evaporation of metallic precursors in presence of elemental sulfur in a two-stage process, was studied by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). It was found that the growth temperature affects the phase in which this compound grows. The samples deposited at temperatures around 500 °C (2nd stage) contain mainly the CuInS2 phase; however, secondary phases like In2S3, Cu2S were additionally identified at the surface and in the bulk of CuInS2 samples deposited at temperatures greater than 550 °C. Also, the elemental composition of the layers constituting the Glass/Mo/CuInS2/buffer/ZnO structure was studied through Auger electron spectroscopy (AES) depth profile measurements. AES measurements carried out across the Glass/Mo/CuInS2/buffer/ZnO heterojunction gave evidence of Cu diffusion from the CuInS2 layer towards the rest of the layers constituting the device, and of the formation of a MoS2 layer in the Mo/CuInS2 interface. The performance of CuInS2-based solar cells fabricated using CBD (chemical bath deposition) deposited ZnS as buffer layer was compared to that of cells fabricated using CBD deposited In2S3 as buffer.