Preparation of a CuGaSe 2 single crystal and its photocathodic properties.

Chalcopyrite CuGaSe 2 single crystals were successfully synthesized by the flux method using a home-made Bridgman-type furnace. The grown crystals were nearly stoichiometric with a Se-poor composition. Although a wafer form of the thus-obtained single crystal showed poor p-type electrical properties due to such unfavorable off-stoichiometry, these properties were found to be improved by applying a post-annealing treatment under Se vapor conditions. As a result, an electrode derived from the Se-treated single crystalline wafer showed appreciable p-type photocurrents. After deposition of a CdS ultrathin layer and a nanoparticulate Pt catalyst on the surface of the electrode, appreciable photoelectrochemical H 2 evolution was observed over the modified electrode under photoirradiation by simulated sunlight with application of a bias potential of 0 V RHE .