Cd1-xZnxS films suitable for application in photovoltaic devices have been produced by annealing CdS films in vaporous zinc chloride and characterized by optical absorption, X-ray diffraction, energy dispersive X-ray spectroscopy and scanning electron microscopy. The incorporation of Zn in CdS was found to be dependent on the annealing temperature and duration, reaching a concentration as high as 50% (x=0.5) and producing a blue shift of 0.3 eV in bandgap energy. CdTe solar cells fabricated with Cd1-xZnxS showed substantially higher short-circuit current than the cells with CdS as the window layer. The optimal concentration of Zn was found to be around 5%. High efficiencies were obtained in SnO2/Cd1-xZnxS/CdTe cells. (C) 2010 Elsevier B.V. All rights reserved.