Surface sulfurization of Cu(In,Ga)Se-2 (CIGS) thin films was carried out using liquid ditertiarybutylsulfide [(t-C4H9)(2)S: DTBS] to improve the performances of CIGS-based solar cells. The initial CIGS thin films were prepared by using the conventional three-stage co-evaporation process. Characterization by scanning electron microscopy, energy dispersive X-ray spectroscopy line scan, X-ray diffraction, and photoluminescence showed that the electrical and optical properties of the absorber layers were improved after sulfurization. The performances of the solar cells incorporating the CIGS films were remarkably improved when films sulfurized with DTBS were used. The efficiency of the solar cells fabricated with CIGS films increased significantly from 12.4% to 13.6% with an open-circuit voltage of 642 mV, short-circuit current density of 30.95 mA/cm(2), and a fill factor of 68.2%. The improved cell performances can be attributed to the formation of a very thin sulfide layer on the CIGS layer and/or surface passivation by S atoms. (C) 2014 Elsevier B.V. All rights reserved.