Investigation of Cu-Deficient Copper Gallium Selenide Thin Film as a Photocathode for Photoelectrochemical Water Splitting

Polycrystalline thin films of CuGaSe 2 -related Cu-deficient materials were prepared by vacuum co-evaporation. The composition was adjusted in order to prepare copper gallium selenide, abbreviated as CGSe, with an optimal band gap and valence band maximum position for photoelectrochemical water splitting. The effect of the Ga/Cu ratio on the photoelectrochemical properties of CGSe was also studied. With increasing Ga/Cu ratio, the band gap of CGSe became larger, and the valence band maximum position became deeper against the vacuum level. However, an analysis of the photocurrent and onset potential indicated that the Ga/Cu ratio should be less than 3.5 for optimal performance. A Pt-deposited CGSe electrode with a Ga/Cu ratio of 3 showed an onset potential of about 1.1 V vs RHE and an energy conversion efficiency of 0.35% under AM 1.5G light illumination in a 0.1 M Na 2 SO 4 solution with pH 9.5.