Room-Temperature Spin Splitting Enabled by Thermally Activated Symmetry Breaking in Two-Dimensional Hybrid Perovskites

Abstract We report a combined computational−experimental study that identifies and explains the enhanced spin splitting in single-layered (n = 1) two-dimensional (2D) lead−iodide hybrid perovskites. We develop a high-throughput screening workflow for experimentally synthesized 2D hybrid perovskites and identify 12 compounds with spin splitting, among which (2-BrPEA)2PbI4 exhibits the largest splitting energy. To establish a unified structure-splitting relationship, we introduce a root-mean-square deviation (RMSD)-based descriptor defined as the deviation between a structure and its inverted counterpart, which correlates with spin-splitting energy more strongly than conventional bond-angle metrics. Notably, although the reported room-temperature structure of (2-BrPEA)2PbI4 is nominally centrosymmetric, it shows strong circularly polarized luminescence (CPL) at room temperature, comparable to the benchmark (4AMP)PbI4. Ab initio molecular dynamics (AIMD) simulations further reveal thermally activated dynamical distortions that transiently break inversion symmetry and amplify spin splitting, establishing lattice dynamics as a key driver of room-temperature spin functionality in 2D hybrid perovskites.