Copper gallium diselenide photocathodes for solar photoelectrolysis

Copper chalcopyrite films exhibit properties suitable for solar energy conversion processes such as direct bandgap, and excellent carrier transport. To explore the possibilities of solar-powered hydrogen production by photoelectrolysis using these materials, we have synthesized p-type polycrystalline CuGaSe2 films by vacuum co-evaporation of the elemental constituents, and performed physical and electrochemical characterizations of the resulting films and electrodes. Based on CuGaSe2 material with 1.65 eV bandgap, a 2.2 micron thick electrode exhibited an outdoor 1-sun photocurrent of 16 mA/cm2, while a 0.9 micron thin device still produced 12.6 mA/cm2 in conjunction with vigorous gas evolution. Flatband potential measurements and bias voltage requirements for saturation photocurrents indicate a valence band position to high for practical device implementation. Future photoelectrolysis devices may be based on copper chalcopyrites with lower valence band maximum in conjunction with a suitable auxiliary junction.