Sb2(S,Se)3 is a highly available energy material with a tunable bandgap by adjusting the S/Se ratio. Increasing the Se ratio can enhance the efficiency of Sb2(S,Se)3 solar cells, with a higher short-circuit current (JSC). However, the accompanying decrease in the open-circuit voltage (VOC) restricts further improvement. The defect passivation is important, since it can reduce carrier recombination, enhancing the VOC. In this study, the relevance of the S/Se ratio, defect concentration, and VOC was investigated. The samples with or without the deposition of Se-rich Sb2(S,Se)3 onto S-rich Sb2(S,Se)3 were used for defect characterization. Different surface compositions were confirmed by Raman spectroscopy. The complicated subdefect states of S-rich Sb2(S,Se)3 were shown through photoluminescence and conductive atomic force microscopy, and a decrease in the defect concentration was observed through surface photovoltage. The improvement of JSC via bandgap grading and the simultaneous VOC improvement by defect passivation resulted in efficient cell performance.