For the realization of vacuum in-line process in the fabrication of Cu(In,Ga)Se-2 (CIGS) solar cells, In2S3 thin film buffer layers for CIGS have been deposited on glasses and CIGS layers with a thickness of about 650 angstrom by thermal evaporation process. During the thermal evaporation, the temperature of the substrate was varied from room temperature to 500 degrees C by heating and the grown In2S3 films were investigated and analyzed in terms of the optimized buffer layer for CIGS solar cells. From the results of scanning electron microscope and X-ray diffraction, the In2S3 thin film deposited at a higher substrate temperature showed the larger grain size and the films have amorphous structural characteristics. Although the structural characteristics such as the atomic ratio of In to S and transmittance of the In2S3 thin films were not proportional to temperature, it was possible to obtain the large optical band gap of In2S3 films of about 3.8-3.9 eV enough to be used as the buffer layer of CIGS. (C) 2013 Elsevier B.V. All rights reserved.