Tailored Band Alignment for Improved Carrier Transport in Composition-Controlled Sb 2 (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.