Introducing a protective interlayer of TiO2 in Cu2O–CuO heterojunction thin film as a highly stable visible light photocathode

Abstract

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.