Designing a Dimension Reduced Hybrid Perovskite with Robust Large Birefringence by Expanding Cationic π‐Delocation

Abstract It is in great demand to discover new materials with large birefringence for the miniaturization of optical communication devices. In this work, a new one‐dimensional hybrid halide perovskite, (C 6 N 10 H 8 )Pb 2 Br 6 , is obtained successfully through structural design of dimension reduction from the notable three‐dimensional halide perovskite CsPbBr 3 . Remarkably, (C 6 N 10 H 8 )Pb 2 Br 6 exhibits a significantly enhanced birefringence of ∆ n = 0.42@550 nm, which is the largest among halide perovskites so far. Furthermore, its birefringence performance is robust in a wide temperature range of 300–440 K. Theoretical calculations reveal that this outstanding birefringence results from the synergistic effect of [PbBr 6 ] 4− octahedra and [C 6 N 10 H 8 ] 2+ cations with expanding π ‐delocation. According to further structural analyses, the structural dimension reduction cooperating with the increase of [PbBr 6 ] 4− octahedral distortion leads to the enhanced birefringence. This work uncovers the great promise of hybrid halide perovskites as robust birefringent crystals in future optical communication and would shed useful insights on the design and synthesis of new birefringent crystals.