The interface between CuInSe2 and i ZnO as it is needed for new chalcopyrite concepts like superstrate and tandem solar cells is investigated with X ray photoelectron spectroscopy. A specially developed preparation permits depth pro amp; 64257;ling of the underlying i ZnO layer. Thereby, interfacial reactions are revealed by tracing the diffusion of Cu, In and Se through the i ZnO. Formation of an In2O3 layer in between i ZnO and CuInSe2 is shown for deposition temperatures of 480 amp; 9702;C and 520 amp; 9702;C. The experiments and thermodynamical ChemSage simulations indicate that this In2O3 layer already forms at 330 amp; 9702;C during the amp; 64257;rst physical vapor deposition step. So far In2O3 formation was believed only to occur at temperatures above 500 amp; 9702;C. An increase of Cu diffusion into the i ZnO with deposition temperatures above 500 amp; 9702;C can be explained with additional formation of ZnkIn2Ok 3 k 5 or k 7 phases