Halogen Substitution as a “Chirality Editor” for Amplifying Spin‐Selective Transport in Lead‐Free Metal‐Halide Hybrids

ABSTRACT Lead‐free metal‐halide hybrids hold promise as flexible semiconductors for X‐ray detection, but their application is constrained by inefficient carrier transport. Here, we introduce halogen substitution on chiral molecular cations as a “chirality editor” to modulate the chiral electrostatic environment and thereby amplify spin‐selective transport in bismuth‐based hybrids. A series of nine ( S / rac / R ‐XPEA) 4 Bi 2 I 10 compounds, where X = F, Cl, or Br and XPEA = 1‐(4‐halophenyl)ethylamine, is systematically investigated, revealing that substitution from F to Br modulates molecular dipoles and local structural distortions, and enhances Rashba spin splitting. Consequently, chiroptical activity increases by nearly one order of magnitude and spin polarization efficiency rises from 68% to 89%, as confirmed by magnetoconductive atomic force microscopy. The amplified chiral‐induced spin selectivity (CISS) effect yields a 3.4‐fold enhancement in carrier mobility‐lifetime product ( μτ up to 3.26 × 10 −3 cm 2 V −1 ) while simultaneously reducing dark‐current drift by threefold. The optimized Br‐substituted homochiral flexible X‐ray detector achieves a sensitivity of 8865.82 ± 403 µC Gy −1 cm −2 and an ultralow detection limit of 7.16 nGy s −1 . Overall, this work establishes a structure‐property‐performance framework that positions halogen‐based “chirality editing” as an efficient strategy for high‐performance radiation detectors.