Solvent‐Assisted Heterojunction Interface Passivation via DMSO Modification for High‐Efficiency Sb ₂ Se ₃ Solar Cells

ABSTRACT Antimony selenide (Sb ₂ Se ₃ ) has recently surpassed the benchmark of 10% power conversion efficiency, establishing itself as a highly promising photovoltaic absorber. However, its further development is largely limited by severe performance losses within the space charge depletion region near the heterojunction interface. Here, we introduce a solvent‐assisted annealing strategy utilizing dimethyl sulfoxide (DMSO) to effectively passivate the surface defects. The DMSO treatment simultaneously removes surface oxides and incorporates trace sulfur into the near‐surface region, thereby neutralizing surface states. Notably, the incorporated sulfur passivates deep‐level selenium vacancy defects V _Se2 and V _Se3 . Theoretical calculations reveal that DMSO chemisorbs onto Sb ₂ Se ₃ via strong Sb─S bonding, which weakens the native Sb─Se lattice and facilitates controlled surface etching. This passivation of interface regions significantly improves the heterojunction quality, yielding a champion power conversion efficiency of 10.48%, corresponding to a 17% relative improvement over the control device (8.99%). This work presents a simple yet effective route to defect mitigation in Sb ₂ Se ₃ photovoltaics, supporting their development toward practical application.