The performance of thermally deposited Sb2Se3 solar cells are severely limited by various bulk and interfacial recombination, instigating a large open-circuit voltage (V-OC) deficit. Ternary Sb-2(S,Se)(3) is considered as a remedy, however, it is also subjected to a dilemma that improvement in V-OC will be escorted by J(SC) loss due to the shrinkage of light harvest. Thus, a gradient of S/Se across the film is a prerequisite to avoid this detrimental compromise. Herein, the incorporation of S in the Sb2Se3 absorber layer evaporated from a CdS buffer layer during vapor transport deposition (VTD) process, and its further self-activated diffusion at the interface upon ambient storage is explored. For the gradient indium tin oxide (ITO)/CdS/Sb-2(S,Se)(3)/Sb2Se3/Au solar cell, the large bandgap Sb-2(S,Se)(3) at the heterojunction side contributes to high V-OC, while the narrow bandgap Sb2Se3 at the top side confirms high J(SC). Sulfur diffusion at the CdS/Sb2Se3 interface also improves the junction quality with an enlarged V-bi, reduced interfacial defects and recombination loss, thus improving V(OC )from 393 to 430 mV. Such V-OC represents the highest value for that of thermally deposited Sb2Se3 solar cells. The champion device also delivers an interesting efficiency of 7.49%. This research provides substantial guidance in exploring efficient approaches to improve the performance of Sb2Se3 solar cells.