Localized Lattice Expansion of FAPbBr 3 to Design a 3D Hybrid Perovskite for Sensitive Near-Infrared Photodetection.

A mixed-cation 3D lead bromide hybrid perovskite (NMDAP) 2 FAPb 4 Br 13 (1, NMDAP 2+ = N-methyl-1,3-diaminopropanium, FA + = formamidinium) is tailored by incorporating the large NMDAP 2+ cation with the small FA + ion into 3D FAPbBr 3 . Structurally, the small FA + ions occupy the prototypical cavities formed by distorted corner-sharing PbBr 6 octahedra as in FAPbBr 3 , while the bulky NMDAP 2+ ions are confined to the expanded lattice which is defined by a new structural motif composed of eight corner-sharing PbBr 6 octahedra and four edge-sharing octahedra. This localized lattice expansion from FAPbBr 3 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 (≈10 4 ) as well as favorable stability.