A precursor layer for Cu(In0.7Ga0.3)Se-2 (CIGS) was deposited by simultaneous sputtering of Cu40In60 and Cu50Ga50 and subsequent sputtering of Cu2Se. The Cu2Se/metal alloy-stacked precursor was selenized at 550 degrees C in a Se vapor atmosphere to grow a CIGS film. The thickness of the Cu2Se layer was varied to control the Cu/(In + Ga) ratio and to study the grain growth behavior. A CIGS film with large grains can be achieved when the overall Cu/(In + Ga) ratio was above 0.92. With the existence of the Cu2Se layer, the Ga concentration was very low near the surface and it was accumulated near the CIGS/Mo interface. Also, the In concentration was very low near the CIGS/Mo interface. As a result, the CuInSe2 phase was formed at the surface and the CuGaSe2 phase was formed near the CIGS/Mo interface. The open-circuit voltage and fill factor were greatly reduced by the Ga segregation. Further supply of Ga on the selenized CIGS film reduced Ga segregation and improved the cell efficiency. (C) 2009 The Electrochemical Society. [DOI:10.1149/1.3258660] All rights reserved.