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 <i>n</i> > 1 to synthesize three new polar 2D lead iodide perovskites (2FBZ)₂(A)_<i>n</i>-1Pb_<i>n</i>I_3<i>n</i>+1 with A = methylammonium (MA) or formamidinium (FA) and <i>n</i> = 2, 3. Single-crystal structure analysis reveals the <i>C</i>_2v 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 (<i>n</i> > 1) halide perovskites to realize new classes of multifunctional materials for future spin-orbitronic applications.