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

Abstract 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 PbI 6 4− 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.