Tailored Band Alignment for Improved Carrier Transport in Composition-Controlled Sb₂(S,Se)₃

Sb-2(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 Sb-2(S,Se)(3) solar cells, with a higher short-circuit current (J( SC)). However, the accompanying decrease in the open-circuit voltage (V (OC)) restricts further improvement. The defect passivation is important, since it can reduce carrier recombination, enhancing the V-OC. In this study, the relevance of the S/Se ratio, defect concentration, and V(OC)was investigated. The samples with or without the deposition of Se-rich Sb-2(S,Se)(3) onto S-rich Sb-2(S,Se)(3) were used for defect characterization. Different surface compositions were confirmed by Raman spectroscopy. The complicated subdefect states of S-rich Sb-2(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 J (SC) via bandgap grading and the simultaneous V- OC improvement by defect passivation resulted in efficient cell performance.