The structure, morphology and optical properties of copper indium sulfide thin films prepared by a novel modulated flux deposition procedure have been investigated for layers from 200 to 400 mn thickness. These polycrystalline CuInS2 films grown onto glass substrates showed CuAu-like structure, similar to epitaxial CuInS2 films grown onto monocrystalline substrates, and direct band gap values Eg=1.521.55 eV, optimum for single-junction photovoltaic applications. The increase in the layer thickness leads to growth of the average crystallite size and increases slightly the surface roughness and the absorption coefficient. (c) 2004 Elsevier B.V. All rights reserved.