A Low-Cost NiO Hole Transfer Layer for Ohmic Back Contact to Cu2 O for Photoelectrochemical Water Splitting.

Cuprous oxide (Cu2 O) photocathode is reported as a promising candidate for photoelectrochemical water splitting. The p-type Cu2 O usually forms a Schottky junction with the conductive substrate due to its large work function, which blocks the collection of photogenerated holes. NiO is considered as one of the most promising hole transfer layers (HTL) for its high hole mobility, good stability, and easy processability to form a film by spin coating. The utilization of NiO HTL to form an Ohmic back contact to Cu2 O is described, thus achieving a positive onset potential of 0.61 V versus reversible hydrogen electrode and a twofold increase of solar conversion efficiency.