We investigated the influence of Sb dopant concentration on the structural, electrical, and photoelectrochemical properties of the photocathode cuprous oxide (Cu2O) thin films. The photoabsorber p-type Cu2O films were prepared by electrodeposition in ionic electrolytes including copper sulfate and antimony sulfate at 333 K and pH = 10. The small amount of Sb doping contributes to the fast Cu ion transport to the substrate and ion consumption; consequently, the p-type Cu2O with high crystalline quality can be reproducibly synthesized with high electrical stability. Among the various samples, the mole fraction of c(Sb)/[c(Cu) + c(Sb)] = 0.75 mol% exhibits the best electrical resistivity and improved transparency in the infrared region, which is involved with the fast overlap of the nuclei crystals under 5 nm from the high nuclei density. Additionally, the post-thermal annealed Sb-doped Cu2O sample reveals an enhanced photocurrent of similar to 0.65 mA/cm(2) vs. RHE (reversible hydrogen electrode) without metal catalysts.