Bulk Photovoltaic Effect Induced by Non‐Covalent Interactions in Bilayered Hybrid Perovskite for Efficient Passive X‐Ray Detection

Hydrogen bonding as a multifunctional tool has always influenced the structure of hybrid perovskites. Compared with the research on hydrogen bonding, the study of halogen‐halogen interactions on the structure and properties of hybrid perovskites is still in its early stages. Herein, a polar bilayered hybrid perovskite (IEA) 2 FAPb 2 I 7 (IEA + is 2‐iodoethyl‐1‐ammonium, FA is formamidinium) with iodine‐substituted spacer is successfully constructed by changing the configuration of interlayer cations and regulating non‐covalent interactions at the organic–inorganic interface, which shows a shorter interlayer spacing and higher density ( ρ = 3.862 g cm −3 ). The generation of structure polarity in (IEA) 2 FAPb 2 I 7 is caused by the synergistic effect of hydrogen bonding and halogen‐halogen interactions. Especially, as the length of the carbon chain in organic cations decreases, the I‐‐‐I interaction in the system gradually strengthens, which may be the main reason for the symmetry‐breaking. Polarity‐induced bulk photovoltaics ( V oc = 1.0 V) and higher density endow the device based on (I‐EA) 2 FAPb 2 I 7 exhibit a high sensitivity of 175.6 µC Gy −1 cm −2 and an ultralow detection limit of 60.4 nGy s −1 at 0 V bias under X‐ray irradiation. The results present a facile approach for designing polar multifunctional hybrid perovskites, also providing useful assistance for future research on halogen‐halogen interactions.