CuO photocathode-embedded semitransparent photoelectrochemical cell

A semitransparent CuO film was applied for photoelectrochemical (PEC) cell to produce the record-high photocurrent (6.4 mA/cm2) for nanocrystalline monoclinic CuO photocathode. Large-scale affordable reactive-sputtering method was effectively formed Cu oxide films and sequential thermal processes efficiently controlled the Cu oxide phases with enhanced optical-transparency of Cu oxide films. Structural, physical, optical, and electrical properties of various Cu oxide films (CuO, Cu4O3, and Cu2O) were systematically investigated according to the sputtering condition and thermal processes. It was found that the energy band gap of CuO can be tuned from 1.7 to 1.9 eV by modulating the oxygen flow for reactive sputtering. Mott–Schottky analyses revealed the flat band potential close to the 0.96 V versus reversible hydrogen electrode and energy band edges of Cu oxide films. This state-of-the-art CuO photocathode would provide a strong potential for wide applications of the transparent PEC system of on-site energy generation.