A section of complete solar cell device consisting of Ag/Al:ZnO/i-ZnO/Cu( In, Ga)Se-2/Mo/glass was in situ annealed inside of TEM column and the interfacial variation was directly investigated in real-time. A pore structure was formed in CdS layer adjacent to CIGS after annealing at 200 degrees C, and the compositional mapping obtained after 300 degrees C annealing showed a heavy diffusion of Ga into ZnO layer. Therefore, Gaassisted Cd diffusion is suggested to be responsible for the pore evolution, which is highly relevant to the device degradation after high temperature annealing. (C) 2010 Elsevier B. V. All rights reserved.