Antimony selenosulfide (Sb2(S,Se)3) is a promising photovoltaic material because of its high chemical stability, optimal optoelectronic properties, and low-cost advantages. However, finding suitable material processing approaches to obtain elemental controlled Sb2(S,Se)3 films with suppressed deep-level defects poses fundamental demands and challenges to developing this emerging solar technology. Here, we developed a robust method for tailoring the composition of the film through controlling the anion elements. The films were prepared by evaporating the presintered Sb2(S,Se)3 alloy compound via a single-source thermal evaporation process. A quasi-precise estimate of single-phase Sb2(S,Se)3 films was made by sintering Sb, S, and Se elemental precursors and adjusting the anion molar ratio in the prefabricated Sb2(S,Se)3 alloy compound, and the elemental ratio of the precursor alloy compound was maintained in the as-obtained Sb2(S,Se)3 films. A highly efficient Sb2(S,Se)3 solar cell with a power conversion efficiency of 8.25% was achieved by introducing low-cost CuPc-doped P3HT as a hole-transporting layer. Here, we demonstrate the dependence of deep-level defects and oriented crystal growth on the S/Se atomic ratios and show how tunability can be used to improve carrier transport for photovoltaic energy conversion. Our study presents a novel approach to fabricating metal chalcogenide semiconducting films and improving the performance of Sb2(S,Se)3 solar cells.