The relatively small band gap approximately 1 eV of CuInSe2 (CIS) restricts the efficiencies of completed CIS/CdS/ZnO solar cell devices. In this study, CuIn(Se,S)(2) thin films were deposited by the reaction of copper-indium alloys with H2Se and H2S gases in Ar at elevated temperatures approximately 450 degreesC. The concentration of the respective reaction gases and exposure periods were optimized in order to produce single-phase material with a controlled distribution of sulfur through the depth of the thin films. X-ray fluorescence in-depth profiling revealed uniform Cu/In atomic ratios and a systematic increase in the sulfur concentration towards the near-surface region of the samples under optimum reaction conditions. The increase in band gap of the absorber layers after sulfurization was also confirmed by low temperature photoluminescence, X-ray diffraction studies as well as optical absorption measurements. (C) 2003 Elsevier Science B.V. All rights reserved.