AbstractIn the past decade, antimony selenide (Sb₂Se₃) has made significant progress as a solar energy conversion material. However, the photovoltage deficit continues to pose a challenge and is a major hurdle that must be overcome to reach its maximum solar conversion efficiency. In this study, various post‐synthetic treatments are employed, of which the combination of a solution phase silver nitrate treatment and sulfurization has shown to be the most effective approach to mitigate the photovoltage deficit in this Sb₂Se₃‐based device. A significant enhancement in the photovoltage is observed after the treatments, as evident by the increase in the onset potential from 0.18 to 0.40 V versus reversible hydrogen electrode. Multiwavelength Raman shows that combining these two treatments removes amorphous Se and metallic Sb from the surface and yields a high‐quality surface layer of Sb₂(S_1−x, Se_x)₃ on the bulk Sb₂Se₃ photoabsorber layer. X‐ray photoelectron spectroscopy with depth profiling reveals extensive incorporation of silver into the film. Density functional theory calculations suggest that silver ions can intercalate between the [Sb₄Se₆]_n ribbons and remain in the Ag⁺ state. This effective treatment combination brings the practicality of the Sb₂Se₃ photocathode for water splitting one step closer to large‐scale applications.