This paper is devoted to an X-ray photoelectron spectroscopy (XPS) study of Cu(In,Ga)Se-2 (ClGSe)/In2S3 Structures. The indium sulphide layers are grown by physical vapor deposition (PVD) in which indium and sulfur are evaporated on the substrates at a temperature T-s. This as-deposited thin films are then heated at 200 degrees C for 1 min. A 12.4% efficiency champion cell has been achieved using this process. The XPS study reveals that copper diffuses from the chalcopyrite absorber towards the indium sulphide layer during this synthesis process. The amount of copper strongly depends on T-s; the higher T-s, the more copper is diffused. This observation is then correlated with the solar cell performance to conclude that a significant Cu-diffusion inhibits the formation of a high-quality junction between the Cu(In,Ga)Se, and the buffer layer. (c) 2004 Published by Elsevier B.V.