2D Multilayered Perovskite Ferroelectric with Halogen Bond Induced Interlayer Locking Structure toward Efficient Self‐Powered X‐Ray Detection

2D Ruddlesden-Popper (RP) hybrid perovskite ferroelectrics have emerged as a promising class of direct X-ray detection materials. However, their intrinsic van der Waals gaps result in weak interlayer interactions that destabilize the layered motifs impacting the stability of the X-ray detector. Thus, it is crucial but remains toughly challenge to enhance interlayer interactions exploring stable RP perovskite ferroelectric X-ray detectors. Here, halogen bond is proposed to enhance the interlayer interactions of RP perovskite ferroelectrics obtaining a 2D trilayered ferroelectric, (BrPA)₂(EA)₂Pb₃Br₁₀ (BEPB, BrPA = 3-bromopropylaminium; EA = ethylammonium). Strikingly, the strong Br···Br halogen bonds lock cations to the inorganic skeletons, and C─H···Br hydrogen bonds bridge adjacent spacing sheets, which effectively improves structural stability and suppresses ion migration. The typical P-E hysteresis loops reveal its concrete ferroelectric behaviors, giving a large polarization of ≈7.3 µC cm^-2. Consequently, the BEPB-based X-ray detector results in a high sensitivity of 562.6 µC Gy^-1 cm^-2 at 0 V bias, and most importantly, it exhibits low baseline drift and exceptional environmental stability. As far as is known, halogen bond strengthening 2D multilayered ferroelectric to achieve stable and efficient X-ray detection is unprecedented, which sheds light on the future design of stable optoelectronic devices toward practical applications.