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

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-FPEAPbI and PEAPbI, 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-FPEAPbI. 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.