A solution growth method for the deposition of Cu-doped zinc-indium-sulfide (ZnIn2S4) semiconductor film electrodes is presented. The structural, optical, and photoelectrochemical (PEC) properties of samples were studied as a function of Cu content in samples. The X-ray diffraction pattern of the cubic ZnIn2S4 phase of an undoped sample was obtained. No Cu alloys or other binary compounds that included the Cu element were present in Cu-doped ZnIn2S4 samples. Images from a scanning electron microscope and atomic ratios of elements in samples obtained from the energy dispersion analysis of X-ray reveal a change in surface morphology and composition for Cu-doped ZnIn2S4 samples. The direct energy band gaps, indirect energy band gaps, and thicknesses of samples prepared in this study varied in the ranges 2.07-2.58 eV, 1.60-2.06 eV, and 521-879 nm, respectively. The maximum photoelectrochemical response of samples in 0.5 M K2SO4 aqueous solution reached 1.15 mA cm(-2) at an external potential of +1.0 V vs. an Ag/AgCl reference electrode under illumination using a 300-W Xe lamp with light intensity kept at 100 mW cm(-2). The experimental results show that Cu doping with Cu/(Cu+Zn) atomic ratio of 0.08 in samples improves the performance of the ZnIn2S4 photoabsorber for PEC applications. Crown Copyright (C) 2011 Published by Elsevier B.V. All rights reserved.