Stacked layers of CuGaSe2 and CuInSe2 grown in slightly Cu-rich conditions were compared to corresponding CuGaSe2 and CuInSe2 single layers using cross-section SEM and TEM analysis as well as XRD. All samples were grown both on Mo coated soda-lime glass substrates and on Mo coated glass substrates with an AI(2)O(3) barrier blocking Na outdiffusion. We found a difference in both grain structure and Ga-In interdiffusion behaviour depending on if Na was present or not during growth. In the Na-free case we found evidence of recrystallisation of the underlying CuGaSe2 layer during the subsequent CuInSe2 growth. In this case also the interdiffusion of In and Ga was enhanced as compared to the sample grown in the presence of Na. (C) 2003 Elsevier Science B.V. All rights reserved.