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

It is still challenging to stabilize α‐FAPbI 3 perovskite for high performance optoelectrical devices. Herein, a novel strategy is proposed utilizing the synergetic electrostatic and steric effect to stabilize the α‐FAPbI 3 phase and suppress the ion migration. Dimethylamine (DMA + ) cations are chosen as the dopant to fabricate FA 0.96 DMA 0.04 PbI 3 single crystals (SCs). DFT calculations reveal that DMA + cations can improve the stability of α‐FAPbI 3 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.