Ultralow Ion Migration and X‐Ray Response from Strong Dipole Moments in (Br‐EA) ₂ PbBr ₄ Perovskite Single Crystals

Abstract 2D hybrid perovskites composed of quantum‐well structures demonstrate immense potential in optoelectronics because of their unique combination of environmental stability and optoelectrical properties. However, improving electrical properties via quantum‐well engineering results in severe ion migration and inferior chemical stability. In this study, a novel strategy to avoid the above trade‐off between electrical properties and stability for modifying the electric field profile in perovskites through molecular design is proposed. To this end, ethylammonium (EA) cations are substituted with 2‐bromoethylamine (Br‐EA) cations and fabricate pure 2D perovskite (Br‐EA) ₂ PbBr ₄ single crystals. The molecular dipole moments of the Br‐EA cations and induced electric field impart several novel features to the X‐ray response, including a ferro‐response current, reverse current, and super‐high V _oc of 95 V. The resulting X‐ray detectors achieve a sensitivity of 540.7 µC Gy _air ⁻¹ cm ⁻² with an extra 38.1% gained from local dipoles, an impressive limit of detection of 9.8 nGy _air s ⁻¹ , and an ultralow dark current drift of 3.69 × 10 ⁻⁸ nA cm ⁻¹ s ⁻¹ V ⁻¹ at −100 V. This study presents valuable insights into the novel effects of dipole moments of A‐site cations on the properties of perovskite materials and inspires further exploration of their potential applications.