A Hybrid Halide Perovskite Birefringent Crystal
Weiqi Huang, Xu Zhang, Yanqiang Li, Yang Zhou, Xin Chen, Xiaoqi Li, Fafa Wu, Maochun Hong, Junhua Luo, Sangen Zhao
Abstract
Abstract Birefringent crystals that can modulate the polarization of light play a significant role in modern optical devices including polarizing microscopes, optical isolators, and achromatic quarter‐wave plates. To date, commercial birefringent crystals are exclusively limited to purely inorganic compounds. Here we report a new organic–inorganic hybrid halide, MLAPbBr 4 (MLA=melamine), which features a (110)‐oriented layered perovskite structure. Although the 6s 2 lone‐pair electrons of Pb 2+ cations are stereochemically inert, MLAPbBr 4 exhibits a birefringence of 0.322@550 nm, which exceeds those of all commercial birefringent crystals. The first‐principles calculations reveal that this birefringence should be ascribed to the highly dislocated π‐conjugation of MLA cations and high distortion of PbBr 6 octahedra. This work highlights the persistently neglected great potential of hybrid halide perovskites as birefringent crystals.