Surface sulfurization was developed as a technique for fabricating efficient ZnO : Al/ CdS/graded Cu(In,Ga)(S,Se)(2)/Mo/glass solar cells. Prior to the sulfurization, single-graded Cu(In,Ga)Se-2 (CIGS) films were deposited by a multi-stage process. The sulfurization of CIGS films was carried out using a H2S-Ar mixture at elevated temperatures. The crystallographic and compositional properties of the absorber layers were investigated by XRD, SEM and AES analyses. After sulfurization, sulfur atoms were substituted for selenium atoms at the surface layer of CIGS films to form a Cu(In,Ga)(S,Se)(2) absorber layer. The diffusion of sulfur depends strongly on the grain structure of CIGS film. The cell efficiency of the 8-11% range before sulfurization was improved dramatically to 14.3% with V-oc = 528 mV, J(sc) = 39.9 mA/cm(2) and FF = 0.68 after the sulfurization process.