In recent years, Sb₂(S,Se)₃ has been considered a promising photovoltaic material due to its excellent photovoltaic properties. However, the highest reported photoelectric conversion efficiency (PCE) of Sb₂(S,Se)₃ solar cells still lags far behind its theoretical PCE limit, partly due to severe carrier recombination in Sb₂(S,Se)₃ films. In this study, a process additive, formamidinesulfinic acid (FSA), was introduced into the precursor solution of Sb₂(S,Se)₃ by hydrothermal deposition method. The additive FSA not only optimizes (211) and (221) orientations as well as Se/S atomic ratio of Sb₂(S,Se)₃ films, but also reduces Sb₂O₃ content of carrier recombination center in the films. The dark saturation current density (J₀) and recombination resistance (R_rec) values of the solar cell with FSA are 1.10×10^-5 mA·cm^-2 and 3147 Ω·cm^-2, respectively, which are significantly better than those of reference device (5.17×10^-5 mA·cm^-2 and 974.3 Ω·cm^-2), indicating that the carrier recombination loss of Sb₂(S,Se)₃ solar cell is restricted. Under AM 1.5G, the mean values of open circuit voltage (V_OC), short circuit current density (J_SC), fill factor (FF), and PCE for the solar cell with FSA are 0.69 V, 18.46 mA·cm^-2, 63.60%, and 8.04%, respectively, showing significant improvement compared to reference device (0.67 V, 17.82 mA cm^-2, 62.27%, and 7.70%). The best device contributes the highest PCE of 8.21%, and this unpackaged device maintains 82.1% of its initial efficiency after a 120 d aging test in air.