Structural dimension engineering and high-temperature dielectric–optical switching in fluorine-substituted lead bromide hybrid perovskites

Abstract

Hybrid metal halide perovskites with structural diversity and solution processability have been widely investigated for many application scenarios. Recently, fluorine substitution has been developed as an effective path to constructing high-performance molecular phase transition materials. However, reports on the structural dimension engineering and high-temperature phase transition properties of hybrid perovskites by fluorine substitution are rare. Herein, (R-3-FPD)PbBr₃ (R-3-FPD = R-3-fluoropiperidinium) and (3,3-DFPD)₂PbBr₄ (3,3-DFPD = 3,3-difluoropiperidinium) were successfully prepared by H/F substitution of two-dimensional (2D) layered (PD)₂PbBr₄ (PD = piperidinium) as the parent, which exhibits no observed phase transition behavior. Monofluoride substituted (R-3-FPD)PbBr₃ shows a dimensionally reduced one-dimensional (1D) perovskite structure because of the introduction of a chiral organic motif and exhibits high-temperature solid–solid phase transition at 410 K. After further difluoride substitution, (3,3-DFPD)₂PbBr₄ reverts to the 2D layered perovskite stacking and exhibits phase transition at around 363 K. Besides, they both demonstrate prominent dielectric switching in cycles at around the phase transition point (T_c). Particularly, stable second-order nonlinear optical switching has been observed in (R-3-FPD)PbBr₃. This finding provides important inspiration for designing phase transition materials with great application prospects in switch devices.