Out-of-Plane Polarization in a 2D Ruddlesden-Popper Hybrid Lead Halide Perovskite Ferroelectric Semiconductor

Lead halide hybrid perovskite ferroelectric semiconductor materials with out-of-plane polarization show great advantages in ultrathin photoelectric devices, especially vertical sandwich-type ferroelectric devices. However, out-of-plane polarization in lead halide hybrid perovskite ferroelectrics is extremely rare, even for the Ruddlesden-Popper (RP) type. Here, we report an RP lead-based hybrid perovskite ferroelectric semiconductor [3,3-difluoropyrrolidium]₂PbBr₄ (DPB) with P_s = 1.65 μC cm^-2 and good X-ray photodetection stability. Notably, it shows the out-of-plane ferroelectric polarization, which is the first time for the RP lead halide ferroelectric family. Our study gives deep insight into ferroelectric polarization and provides the potential probability for the miniaturization and integration of ferroelectric photoelectric devices.