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Antimony selenide (Sb 2 Se 3 ) has attracted considerable attention for its simple composition, nontoxic nature, and abundance. However, the efficiency of Sb 2 Se 3 solar cells is limited by the low carrier concentration and high recombination rate at the interface between Sb 2 Se 3 and the Au layer. For this paper, the KOH solution used as the etchant was used to increase the efficiency of Sb 2 Se 3 solar cells. The KOH solution not only reacts with (etching the surface) but also diffuses inside the Sb 2 Se 3 film. This study unexpectedly demonstrates that KOH also increases the doping density and improves the back contact (the thin Sb 2 O 3 layer exists with the etching of the KOH solution) of Sb 2 Se 3 solar cells. Lastly, the best power conversion efficiency of 7.16% is demonstrated with a high open-circuit voltage of 0.407 V; we believe our work can serve as a guide for further development of high-efficiency Sb 2 Se 3 solar cells.