Morphological characterization and AES depth profile analysis of CuInS2 thin films

This work presents results regarding the influence of preparation conditions on the morphological properties and on the chemical composition homogeneity of CuInS2 (CIS) thin films, grown by a chemical reaction of the precursor species evaporated sequentially on a soda-lime glass substrate, in a two- or three-stage process. The CIS samples were characterized using atomic force microscopy (AFM), scanning electron microscopy (SEM) and Auger electron spectroscopy (AES) depth profile measurements. The results showed that the deposition process and the ratio (evaporated Cu/evaporated In) affect the homogeneity of the chemical composition of the CIS film as well as the grain size. It was found that the samples grown in two stages are inhomogeneous in chemical composition and also Cu-rich near the film surface, probably due to the formation of a secondary Cu2S phase in the surface region. The results also revealed that adding a third step in the deposition process improved the homogeneity in the chemical composition of CIS films and helped to remove the Cu2S surface layer. The chemical composition of the samples deposited in a three-stage process is homogeneous in the whole volume, whereas the chemical composition in the bulk of samples deposited in a two-stage process is significantly different to that measured in the surface region. CIS films with characteristics found for the former case have demonstrated good properties for its use as absorber layers in thin film solar cells. (C) 2009 Elsevier B.V. All rights reserved.