CuIn1-xGaxSe2 (CIGS) thin films were grown on Mo/soda lime glass using a reactive sputtering process in which a Se cracker was used to deliver reactive Se molecules. The Cu0·6 Ga0·4 and Cu0·4In0·6 targets were simultaneously sputtered under the delivery of reactive Se. The effects of Se flux on CIGS film deposition were investigated. The CIGS film growth rate decreased, and the surface roughness of a film increased as the Se flux increased. The  crystal orientation was dominant, and metallic crystal phases such as Cu9Ga4 and Cu16In9 in a film were disappearing with increasing Se flux. A solar cell fabricated using a 900-nm CIGS film showed the power conversion efficiency of 8·6%, the highest value found in a sub-micron thick CIGS solar cell related to a reactive sputtering process with metallic targets. Copyright © 2011 John Wiley & Sons, Ltd.