The influence of sulfurization treatment in the structural and photovoltaic properties of Cu(In,Ga)(Se,S)(2) films was investigated in this study. X-ray diffraction patterns and secondary ion mass spectrometry results revealed that sulfur-rich Cu(ln,Ga)(Se,S)(2) layers were formed near the surface region of absorber films. Prolonging the duration of sulfurization process increased the amount of sulfur species by replacing the selenium ions of Cu(ln,Ga)Se-2 films. The photoluminescence spectra indicated a significant reduction of selenium vacancies near surface region of Cu(In,Ga)(Se,S)(2) films. The conversion efficiency of fabricated Cu(ln,Ga)(Se,S)(2) solar cells was increased from 9.81% to 11.63% by sulfurization treatment. In a diode analysis, the annihilation of selenium vacancies and the improved morphology reduced the formation of shunt paths, lowering the diode factor and saturated current. This investigation demonstrates that the controlled surface sulfurization effectively improved the photovoltaic performance of Cu(In,Ga)(Se,S)(2) solar cells. (C) 2016 Published by Elsevier B.V.