Halogenated Chiral Organic Spacer Cation Regulation for Efficient and Stable 2D Ruddlesden-Popper Perovskite Solar Cells

2D Ruddlesden-Popper (2DRP) perovskites have emerged as promising candidates for next-generation photovoltaic devices owing to their excellent environmental stability, moisture resistance, and photo-stability. However, their power conversion efficiencies (PCEs) still lag behind those of their 3D counterparts, primarily due to the poor charge-carrier transport associated with the insulating bulky organic spacer cations. In this work, a series of halogenated chiral organic spacers–S-α-fluorophenylethylamine acrylate (S-α-FPEAAA), S-α-chlorophenylethylamine acrylate (S-α-ClPEAAA), and S-α-bromophenylethylamine acrylate (S-α-BrPEAAA)–are employed to regulate charge transport within the 2DRP framework. Incorporating halogen atoms facilitates halogen–halogen interactions between the organic spacers and the PbI₆⁴⁻ octahedral framework, thereby enhancing structural ordering and electronic coupling. Among these, the S-α-BrPEAAA-based perovskites exhibit superior film morphology, improved crystallinity, and an exceptional carrier lifetime of 3.353 µs. Notably, an inverted perovskite solar cell based on S-α-BrPEAAA achieves a high PCE of 20.30%, rivaling the best-performing systems reported recently. Moreover, the device demonstrates excellent long-term stability, retaining over 95% of their initial efficiency after 2000 h of storage under nitrogen atmosphere. These findings highlight the potential of halogenated chiral organic spacers in advancing high-performance and stable 2D perovskite photovoltaics.