Perovskitizer Tuning Pb²⁺ 6s² Lone Pair Effects in Hybrid Perovskite Halide Enables Multiaxial Self‐Powered X‐Ray Detection

The stereochemical expression of the n s 2 lone pair significantly impacts symmetry breaking and corresponding photoelectric properties. However, hindered by the symmetric octahedral configuration, the Pb 2+ 6s 2 lone pair in the well‐conductive lead halide hybrid perovskites (LHHP) are normally stereo‐inactive, new approaches to activate the 6s 2 lone pair are still greatly desired. Herein, by exploiting a perovskitizer tuning Pb 2+ lone pair method, the study successfully obtains a stereo‐active 6s 2 in the polar perovskite PA 2 MHy 2 Pb 3 Br 10 (PMPB, PA = n‐propylamine, MHy = methylhydrazine), and unprecedentedly performs a multiaxial self‐powered X‐ray detection. In detail, the stereo‐active 6s 2 lone pair is caused by the coordination bond between the perovskitizer MHy and Pb atom. Emphatically, the N‐Pb bond induces a large angular distortion parameter (≈45 times larger than other LHHP) and the lowest‐symmetric space group ( P 1) crystallization. Therefore, PMPB natively contains multiaxial polarization, which acts as the driving force to separate and transport the X‐ray‐generated carriers, thus enabling multiaxial self‐powered X‐ray detection with a low detection limit (129 nGy s −1 ). This work reveals the relationship between stereo‐active lone pair and polarization and sheds light on future X‐ray detection.