Defect‐Cluster‐Boosted Solar Photoelectrochemical Water Splitting by n‐Cu₂O Thin Films Prepared Through Anisotropic Crystal Growth

Abstract

Abstract Anisotropic growth of Cu 2 O crystals deposited on an indium‐doped tin oxide‐coated glass substrate through facile electrodeposition and low‐temperature calcination results in favorable solar photoelectrochemical water splitting. XRD, TEM, and SEM reveal that appreciable oxygen vacancies are populated in the Cu 2 O crystals with a highly branched dendritic thin film morphology, which are further substituted by Cu atoms to form Cu antisite defects exclusively along the [111] direction. The post‐thermal treatment presumably accelerates such migration of the lattice imperfections, favoring the exposure of the catalytically active (111) facets. The Cu 2 O thin film derived in this way shows n‐type conduction with a donor concentration in the order of 10 17 cm −3 and a flat‐band potential of −1.19 V vs. Ag/AgCl, which is also confirmed by Mott–Schottky analysis. The material is employed as a photoanode and delivers a photocurrent density of 2.2 mA cm −2 at a potential of 0.3 V vs. Ag/AgCl, surpassing reported values more than twofold. Such superiority mostly originates from the synergism of the selective facet exposure within the Cu 2 O crystals, which have decent crystallinity, as shown by Raman and photoluminescence spectroscopy, and a favorable bandgap of 2.1 eV, as confirmed by UV/Vis spectroscopy. The n‐type Cu 2 O thin film reported herein holds excellent promise for solar‐related applications.