Cu(In,Ga)Se-2 (CIGS) is one of the most promising materials to fabricate low-cost and high-efficiency thin film solar cells. In this work, CIGS films were deposited by the so-called "multi-layer precursor method" using multi-layer co-evaporation of material sources. Based on the simulated and experimental results, the optimum averaged Ga/III, Ga/(In + Ga), in space charge region (SCR) controlling the carrier recombination near the junction and back surface Ga/III grading forming back surface field have drastic influence on cell performance. The CIGS absorber layer with double Ga/III grading profile (averaged Ga/III in SCR; 0.38 and the height of the back surface Ga/III grading; 0.33) is readily achieved by multi-layer precursor method. This leads to the improvement of efficiency of the CIGS solar cell up to 15.30% without anti-reflective layer. (C) 2014 Elsevier B. V. All rights reserved.