Thin films of a solid solution of ZnSe and CuIn0.7Ga0.3Se2 ((ZnSe) (x) (CIGS) (1-x) ) are prepared by co-evaporation. Structural characterization reveals that the ZnSe and CIGS form a solid solution with no phase separation. (ZnSe)(0.85)(CIGS)(0.15)-based photocathodes modified with Pt, Mo, Ti, and CdS exhibit a photocurrent of 7.1 mA cm(-2) at 0 V-RHE, and a relatively high onset potential of 0.89 V-RHE under simulated sunlight. A two-electrode cell containing a (ZnSe)(0.85)(CIGS)(0.15) photocathode and a BiVO4-based photoanode has an initial solar-to-hydrogen conversion efficiency of 0.91%, which is one of the highest values reported for a photoanode-photocathode combination. Thus, (ZnSe)(0.85)(CIGS)(0.15) is a promising photocathode material for efficient photoelectrochemical water splitting.