Introducing a protective interlayer of TiO₂in Cu₂O-CuO heterojunction thin film as a highly stable visible light photocathode

Visible light-induced photocurrent generation and photoelectrochemical stability of p-type Cu₂O-CuO photocathodes are improved significantly upon incorporating an interlayer of TiO₂ between Cu₂O and CuO. The TiO₂ layer hinders the electron conduction at the semiconductor-electrolyte interface (improved stability) as well as promoting electron transfer from Cu₂O to CuO (increased photocurrent). Upon visible light illumination, the optimised multilayer Cu₂O-TiO₂-CuO heterojunction thin film yields a photocurrent of 2.4 mA cm_-2 and retains 75% of its photoactivity over the measurement period. By comparison, the unmodified Cu₂O-CuO generates a photocurrent of 1.3 mA cm^-2 with photoactivity retention of only 32% after prolonged illumination. Wavelength-dependent incident photon-to-current efficiency (IPCE) reveals a considerable enhancement over the excitation region of Cu₂O (400-560 nm). Transient fluorescence decay analysis suggests the promotion of electron transfer from Cu₂O to CuO through TiO₂. As a result, both photoactivity and photochemical stability of the photocathodes are improved.