Optimized Vapor Dynamics Boosts Carrier Transport of Heterojunction: A Novel Strategy for Fabricating Efficient Sb ₂ (S,Se) ₃ Solar Cells

Abstract Sb2(S,Se)3 solar cells have gained plenty of attentions in recent years, however, the efficiency of vacuum derived one is limited by the chalcogen loss during deposition and unstable heterojunction interface. Herein, a mean free path modulation (MFPM) strategy is proposed to solve this problem. Results show that reduced MFP of vapor molecules at higher deposition pressure decreases the film thickness, compactness and crystallinity of Sb ₂ (S,Se) ₃ film. In addition, the diminished MFP and kinetic energy of vapor molecules promote Sb ₂ O ₃ formation, introducing harmful defects like VSe and degrading carrier transportation. By contrast, the interface quality of CdS/Sb ₂ (S,Se) ₃ interface (ΔEC = −0.19 eV) is optimized at 0.5 Pa, meanwhile, the [hk1] orientation and carrier transport of Sb2(S,Se)3 film are enhanced as well. This expands the depletion region of Sb ₂ (S,Se) ₃ device while reducing interface and bulk defects by 50% and two orders of magnitude, respectively. Consequently, the short‐circuit current density (JSC) and power conversion efficiency (PCE) of Sb ₂ (S,Se) ₃ solar cells are improved by 31% and 33%, leading to a PCE of 8.08%, with remarkable JSC of 29.66 mA cm ⁻² —the highest value for VTD‐processed Sb ₂ (S,Se) ₃ solar cells. This study highlighted the potential of MFPM strategy on fabricating efficient compound photovoltaic film and devices.