Synergetic Electrostatic and Steric Effects in α‐FAPbI₃ Single Crystals For X‐Ray Detection and Imaging

Abstract It is still challenging to stabilize α‐FAPbI₃ perovskite for high performance optoelectrical devices. Herein, a novel strategy is proposed utilizing the synergetic electrostatic and steric effect to stabilize the α‐FAPbI₃ phase and suppress the ion migration. Dimethylamine (DMA⁺) cations are chosen as the dopant to fabricate FA_0.96DMA_0.04PbI₃ single crystals (SCs). DFT calculations reveal that DMA⁺ cations can improve the stability of α‐FAPbI₃ phase in both thermodynamics (lower Gibbs free energy) and kinetics (higher defect formation and migration energy). The resulting SCs exhibit an environmental stability over 100 days and an extraordinary low dark current drift of 3.7 × 10⁻⁷ nA cm⁻¹ s⁻¹ V⁻¹, comparable to 2D perovskite SCs. The X‐ray detectors have also achieved the‐state‐of‐the‐art performance in X‐ray detection and imaging. This work demonstrates the significance of electrostatic and steric effects in improving the phase and operational stability of perovskites.