Unraveling the Impact of Organic Cation Dipole Moment on Rashba Spin‐Splitting in 2D Hybrid Organic–Inorganic Perovskites

Abstract Rashba spin‐splitting in hybrid organic–inorganic perovskites (HOIPs) holds great potential for spintronic applications. However, strategies for controlling Rashba spin‐splitting in these materials remain underexplored. Here, we find organic cation dipole moments play a pivotal role in modulating Rashba effects. By comparing p ‐FPEA 2 PbI 4 and PEA 2 PbI 4 , we demonstrate that larger dipole moments amplify lattice distortion and local symmetry breaking, as confirmed by second‐harmonic generation (SHG). This structural asymmetry doubles the Rashba spin‐splitting energy, quantified through the circular photogalvanic effect (CPGE) and circularly polarized light excited photoluminescence (CPLEPL). Circular dichroism (CD) and magnetic circular dichroism (MCD) reveal a Rashba‐induced effective magnetic field, while spin pumping shows a ∼50% higher Rashba coefficient in p ‐FPEA 2 PbI 4 . These results establish a direct correlation between dipole moment and spin splitting in 2D HOIPs, a trend that extends to quasi‐2D and 3D HOIPs. Our work shows dipole engineering as a general design rule for tailoring Rashba effects in HOIPs, paving the way toward high‐efficiency spin‐based optoelectronics and quantum devices.