Direct current sputter deposited CuO layers on conductive glass: Towards a maximum photoelectrochemical response of photocathodes

• Copper oxide films were deposited using reactive direct current magnetron sputtering. • The stoichiometry of copper oxides was tuned by varying the oxygen partial pressure. • Cupric oxide films achieved an incident photon-to-current efficiency of up to 12.3%. This study investigates the photoelectrochemical properties of copper-oxides and their use as photoelectrodes deposited onto conductive glass (fluorine-doped tin oxide) via reactive direct current magnetron sputtering. Through careful optimization of sputtering parameters, we hint that among various phases formed (Cu 2 O, Cu 4 O 3 and CuO), an optimized cupric oxide layer can be grown that sputtered under an oxygen flow rate of 7 sccm exhibits the highest photoelectochemical activity that can reach a maximal incident photon-to-current efficiency of 12.3 %. A key factor in this optimization is the precise control of oxygen partial pressure, which facilitates the crystallization of Cu x O y , leading to enhanced photoelectrochemical performance. Further improvements in efficiency were investigated by varying annealing temperatures and film thicknesses. This work demonstrates a simple yet effective method for fabricating high-efficiency CuO photocathodes.