The photoelectrochemical properties of electrodeposited p-type copper(I) oxide (Cu2O) films were investigated using methyl viologen (MV2+) as an electron acceptor. The pristine Cu2O films were deactivated during the photocathodic reaction as a result of self-reduction, whereas the (111)-oriented Cu2O films treated in an aqueous solution containing hexamethylenetetramine at pH 5 and 90 degrees C exhibited stable photocurrent for MV2+ reduction into the cation radical. Scanning electron microscope images showed that the treated films contained smaller crystal grains than untreated ones. X-ray photoelectron spectroscopy revealed that the treatment etched the thin layer of copper(II) oxide from the Cu2O polycrystalline surface. Etching of the film surface enhanced the stability and steady-state photocurrent for photocathodic reduction of MV2+, suggesting that the crystalline composition and structures exposed on the outermost surface of Cu2O polycrystalline films have a considerable influence on the selectivity for the photocathodic reaction over self-reduction. (C) 2013 Elsevier B. V. All rights reserved.