Introducing a protective interlayer of TiO2 in 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.