Quantitative phase analysis of Cu(In1-xGax)Se-2 (CIGS) thin film grown over Mo coated soda lime glass substrates was studied by Rietveld refinement process using room temperature X-ray data at theta-20 mode. Films were found to contain both stoichiometric Cu(In1-xGax)Se-2 and defect related Cu(In1-xGax)(3)Se-5 phases. Best fitting was obtained using crystal structure with space group I-42d for Cu(In1-xGax)Se-2 and I-42m for Cu(In1-xGax)(3)Se-5 phase. The effects of Ga/III (=Ga/In+Ga=x) ratio and Se flux during growth over the formation of Cu(In1-xGax)(3)Se-5 defect phase in CIGS was studied and the correlation between quantity of Cu(In1-xGax)(3)Se-5 phase and solar cell performance is discussed. (C) 2010 Elsevier B.V. All rights reserved.