Herein, Ni is for the first time put forward as a promising dopant to promote the photoelectrochemical property of cuprous oxide (Cu 2 O) with particularly n-type conduction. An electrochemical route is utilized to deposit Ni:Cu 2 O on the indium tin oxide (ITO) coated glass as a dense thin film with tree-like morphology, as revealed through scanning electron microscopy. Particularly, the incorporation of Ni that is verified via X-ray diffractometry leads to a compressive stress compensating well the tensile strain within Cu 2 O, which originates otherwise from large lattice mismatch between Cu 2 O and ITO. This in turn improves the crystallinity of the Ni:Cu 2 O thin film. More importantly, X-ray photoelectron spectroscopy indicates that the substitution of Ni(II) for Cu(I) boosts the carrier concentration to 8.4 × 10 18 cm −3 , as further evidenced by the Mott−Schottky analysis. Those enhancements along with an advantageous band structure including a flat-band potential of −1.1 V and a bandgap of ∼2.1 eV that is alternatively derived from UV−vis spectroscopy allow Ni:Cu 2 O to deliver an outstanding photocurrent of 2.5 mA cm −2 (at 0.3 V vs Ag/AgCl) for solar water splitting. Such performance well-surpasses those of other reported n-type Cu 2 O photoanodes more than 2fold, attesting the great promise of Ni:Cu 2 O in this work for solar-related applications.

Anisotropic growth of Cu2O 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 Cu2O 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 Cu2O thin film derived in this way shows n‐type conduction with a donor concentration in the order of 1017 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 Cu2O 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 Cu2O thin film reported herein holds excellent promise for solar‐related applications.