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

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.