Constructing p–n Interfaces to Accelerate Carrier Separation in a Cu2O Photocathode through an In Situ Thermal Oxidation Method for Highly Active Photoelectrochemical Properties

Abstract

Cu₂O-ZnO blended films with the structure of ZnO nanoparticles randomly distributed in the Cu₂O matrix were synthesized using an in situ thermal oxidation method. The microstructure and growth mechanism of the prepared Cu₂O-ZnO films were revealed depending on elemental mapping and thermogravimetric analysis. Benefiting from the unique structure, an effective built-in electric field formed at the numerous p–n interfaces, enabling efficient spatial separation of carriers. Consequently, photoelectrochemical evaluation of the Cu₂O-ZnO film performed under chopped simulated AM 1.5G illumination exhibited a high photocurrent of −6.8 mA/cm² at 0 V vs RHE, which was 4.5 times higher than that of bare Cu₂O film. The onset potential was also positively shifted from 0.62 V vs RHE to 0.74 V vs RHE. The introduction of ZnO also resulted in a high carrier density of 1.96 × 10¹⁸ cm^–3 and reduced carrier transfer resistance in an electrolyte. To evaluate the potential of long-term application, a 20 nm TiO₂ protective layer was deposited by a low energy ion beam technique on the Cu₂O-ZnO film; the attenuation of photocurrent was effectively suppressed due to the isolation of the electrolyte. The obtained Cu₂O-ZnO blended films with rich p–n interfaces may serve as a good light absorber and carrier provider for use in photoelectric conversion and photoelectrochemical applications.