Chirality‐Induced Spin Optimization in Lead‐Free Metal‐Halide Hybrids for High‐Performance Flexible X‐Ray Detectors

Lead‐free metal‐halide hybrid x‐ray detectors are fundamentally limited by strong exciton localization and inefficient carrier transport, preventing their deployment in high‐sensitivity flexible imaging systems. Here we establish a chirality‐modulated spin‐engineering strategy that intrinsically overcomes these limitations by quantitatively linking molecular chirality, Rashba spin splitting, carrier transport, and detector performance in a chiral Bi/Sb metal‐halide hybrid series, ( S 1−r R r ‐CHEA) 4 (Bi 0.5 Sb 0.5 ) 2 I 10 (CHEA = 1‐cyclohexylethylamine), where the enantiomeric ratio functions as a continuous structural control parameter. Homochiral assemblies maximize inversion‐symmetry breaking, producing a giant Rashba coefficient up to 0.41 eV Å −1 and enabling long‐lived (> 1 ns) spin polarization that suppresses excitonic localization. As a result, the exciton binding energy decreases by 42% while the carrier mobility–lifetime product ( μτ ) increases fourfold, establishing an intrinsic spin‐modulated transport mechanism in lead‐free metal‐halide hybrids. Flexible detectors fabricated from the optimized homochiral composition exhibit deformation‐invariant x‐ray imaging with a record sensitivity of 8002 µC Gy −1 cm −2 , an ultralow detection limit of 75 nGy s −1 , and exceptional robust endurance under couples of stresses including thermal, humidity, mechanical, and irradiation. This work identifies molecular chirality as a programmable handle to control spin–orbit interactions and carrier dynamics, providing a general materials‐level strategy for high‐performance, environmentally benign radiation detectors and spin‐enabled optoelectronics.