Over 10% efficiency Sb2(S,Se)3 solar cells by enhancing the depletion width and interface passivation via methanol-assisted surface treatment

Abstract

Antimony selenosulfide (Sb₂(S,Se)₃) has emerged as a promising absorber for thin-film solar cells, yet its power conversion efficiency (PCE) remains far below the theoretical limit, primarily due to inefficient carrier collection and interface recombination losses. Hydrothermal synthesis, commonly used in state-of-the-art Sb₂(S,Se)₃ solar cells, often induces surface band bending that impedes charge transport. In this study, we introduce a mild aqueous surface etching treatment (SET) as a simple and effective strategy to mitigate the undesirable surface band bending of hydrothermally grown Sb₂(S,Se)₃ and improve interfacial electronic properties. While strong alkaline solutions can etch antimony chalcogenides via hydroxide ions, we demonstrate that deionized water (DIW) alone can act as a mild etchant, removing the top surface region without disrupting the S/Se composition throughout the remaining absorber. The etching efficacy is further enhanced by the addition of methanol to DIW, which creates a more alkaline etching environment, accelerates the etching process, and promotes the surface passivation. The passivation of deep-level and interfacial trap states is confirmed by three-dimensional deep-level transient spectroscopy (3D-DLTS). Capacitance–voltage profiling further reveals a widened depletion region and reduced doping density. As a result, the champion device achieves a PCE of 10.05%, with notable gains in short-circuit current density and fill factor. This work demonstrates that methanol-assisted SET provides a simple and effective route for interface engineering, offering broad applicability to chalcogenide thin film solar cell technologies.