An insurmountable disadvantage of CuInSe2 is the low band gap, which limits the open-circuit voltage to value well below 500 mV in solar cells. The incorporation of sulfur into CuInSe2 thin film was investigated to establish a scientific basis for the graded band gap CuIn(Se1-x,S-x)(2) thin films. CuIn(Se1-x,S-x)(2) thin films were obtained by reactive annealing of Cu11In9 precursors in a mixture of sulfur and selenium atmosphere while post-sulfurization of single phase CuInSe2 did not result in CuIn(Se1-x,S-x)(2) thin films. A band gap of 1.36 eV, was obtained for the prepared CuIn(Se1-x,S-x)(2). (C) 2006 Elsevier B.V. All rights reserved.