Organic molecular orientation enables intrinsic defect passivation in CH3NH3PbI3 perovskite

The orientation of organic CH3NH3 (MA) molecules is a key factor influencing the structural and electronic properties of hybrid perovskites. Here, we contrast ferroelectric (FE) and antiferroelectric (AFE) MAPbI3 using quantum dynamics simulation to investigate the behavior of interstitial iodine (Ii) under different MA orientations. In the FE structure, unidirectional orientation stabilizes an iodine trimer that induces a deep trap state. In the AFE structure, antiparallel orientation induces local compression of the Pb–I framework, intrinsically blocking iodine aggregation and suppressing the formation of the trap state. Similar behaviors are also supported by charged Ii defect (Ii−1 and Ii+1) conditions. Moreover, the AFE structure exhibits more localized valence band maximum, faster decoherence, and reduced nonadiabatic coupling, thereby extending carrier lifetimes by more than fivefold when compared to the FE structure. This work provides a direct physical basis for defect sensitivity dependent on organic molecular orientation and offers clear design guidance for orientation engineering toward more defect-tolerant perovskite devices.