The absorber/buffer interface is essential for high-performance thin film chalcopyrite solar cells. In this contribution we present studies of interface formation between Cu(In,Ga)Se-2 with 30 and 100% Ga content and the II-VI semiconductor CdS using in situ photoelectron spectroscopy. Clean Cu(In,Ga)Se-2 surfaces with a Cu-deficient surface composition were prepared by heating-off of Se layers, which were deposited onto the absorber layers in the deposition chamber directly after absorber deposition. Interfaces with CdS were prepared by stepwise evaporation. The determined band alignments are compared to theoretical calculations. (C) 2003 Elsevier B.V. All rights reserved.