Localized Lattice Expansion of FAPbBr3 to Design a 3D Hybrid Perovskite for Sensitive Near‐Infrared Photodetection

A mixed-cation 3D lead bromide hybrid perovskite (NMDAP)2 FAPb4 Br13 (1, NMDAP2+ = N-methyl-1,3-diaminopropanium, FA+ = formamidinium) is tailored by incorporating the large NMDAP2+ cation with the small FA+ ion into 3D FAPbBr3 . Structurally, the small FA+ ions occupy the prototypical cavities formed by distorted corner-sharing PbBr6 octahedra as in FAPbBr3 , while the bulky NMDAP2+ ions are confined to the expanded lattice which is defined by a new structural motif composed of eight corner-sharing PbBr6 octahedra and four edge-sharing octahedra. This localized lattice expansion from FAPbBr3 creates a new branch of the intriguing 3D hybrid perovskite family, breaking the limits of the conventional Goldschmidt tolerance factor rule. Moreover, a high two-photon absorption (2AP) coefficient of 60.8 cm MW-1 was demonstrated to near-infrared (NIR) 800 nm illumination, enabling sensitive NIR photoresponses with large on/off ratio (≈104 ) as well as favorable stability.