Multifunctional Polar 2D Lead Iodide Perovskites Exhibiting Persistent Spin Texture.

Ferroelectric Rashba semiconductors are a rare class of multifunctional materials promising for spin-orbitronics due to the possibility of electrically switchable spin textures. Hybrid organic-inorganic metal halide perovskites offer exceptional tunability that can be harnessed to target noncentrosymmetry; however, the complex interactions between organic and inorganic components are not rationally understood. Here, we use an asymmetric spacer cation with a strong molecular dipole moment (2-fluorobenzylammonium, 2FBZ) and increase the intrinsic quantum well thickness to > 1 to synthesize three new polar 2D lead iodide perovskites (2FBZ)(A)PbI with A = methylammonium (MA) or formamidinium (FA) and = 2, 3. Single-crystal structure analysis reveals the symmetry of these crystal structures and substantial structural distortions, which enable Rashba and Dresselhaus band splitting and persistent spin texture, confirmed by DFT calculations. Measurements of the resulting symmetry-dependent properties, such as second harmonic generation, switchable photovoltaic effect, ferroelectric polarization, and low temperature photoluminescence show switchable ferroelectric semiconducting properties. These results introduce a general chemical design strategy toward polar symmetry by exploiting the complex interplay between asymmetric spacer cations and A-site cations in quasi-2D ( > 1) halide perovskites to realize new classes of multifunctional materials for future spin-orbitronic applications.