The composition and the microstructure evolutions of CuInSe2 thin films under single-bath electrodeposition processes were investigated. It was found that the film composition was mainly determined by the [Se4+]/[Cu2+] ratios in solution, but the film microstructure is strongly dependent on the initial concentrations of Se4+, Cu2+, and In3+ precursors. Higher initial concentrations of Cu2+ and In3+ in solution are beneficial for the fabrication of compact CuInSe2 thin films with highly crystallized and large grain sized chalcopyrite phase. The microstructure evolution suggests that prior adsorption and reduction of Cu2+ ions and the formation of Cu2Se compound on the substrate can promote the nucleation, growth, and coarsening of CuInSe2 crystal to form a high quality thin film during the electrodeposition processes. (C) 2010 Elsevier B.V. All rights reserved.