A Novel Photocathode Material for Sunlight‐Driven Overall Water Splitting: Solid Solution of ZnSe and Cu(In,Ga)Se₂

Thin films of a solid solution of ZnSe and CuIn 0.7 Ga 0.3 Se 2 ((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 BiVO 4 ‐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.