Effect of Annealing Process on the Heteroepitaxial Cuo/Cu2O as a Highly Efficient Photocathode for Photoelectrochemical Solar Cell Application

Abstract

The thermal oxidations of cuprous oxide were effectively prepared via simply annealing on copper foil substrate Cu₂O photocathodes. They were characterized by Fourier transport infrared spectroscopy (FTIR), scanning electron microscopy (SEM). The results during the annealing process showed that a heteroepitaxial layer of CuO/Cu₂O formed, which displayed the nature of a p-type semiconductor. Compared to pure Cu₂O, the photocurrent density and photoelectrochemical (PEC) stability of the p-type heteroepitaxial CuO/Cu₂O photocathode improved significantly, largely due to changes in annealing time and temperature. The best performance and stability were achieved by annealing at 475°C, showing a considerable enhancement over the as-deposited Cu₂O. This indicates that the CuO/Cu₂O heteroepitaxial layer helps separate electron-hole pairs, boosting both the current and stability of the photocathode. Although the heteroepitaxial layer is thin, its effect on catalytic activity is substantial. It alters the band and electronic structures of Cu-Cu₂O, which aids in activating O₂ and transferring electrons during the oxidation process, thereby enhancing catalysis.