Lead-Free Double Perovskite Semiconductor with Rigid Spacer-Induced High-T_c Dielectric Switch Features

Layered hybrid perovskites possess exceptional semiconductor features and structural versality, making them viable candidates for developing multifunctional dielectric phase-transition materials (PTMS). However, most PTMs based on layered hybrid perovskites still suffer from Pb toxicity and low operating temperature. The recently developed hybrid double perovskites provide a new routine to designed PTMs with desired working performance and environment-friendly chemical compositions. Herein, using rigid aromatic cations as templates, we have successfully synthesized a novel double perovskite (benzylammonium)₄ AgBiBr₈ (1), which consists of corner-sharing AgBr₆ and BiBr₆ layers and benzylammonium cations. Notably, 1 exhibits a high-temperature first-order reversible solid-state phase transition at 383/387 K (cooling/heating) and switchable dielectric performance around the temperature. Compared with the soft organic chain version of the compound, the phase transition temperature of 1 shows a large enhancement of 99 K, validating the correctness of the designing strategy. In addition, 1 also exhibits semiconductor characteristics with a calculated bandgap of 2.34 eV and an optical bandgap of 2.29 eV. Remarkably, the single crystal photodetector of 1 shows a low dark current (2.12×10^-13  A), a high on/off ratio (1.77×10³ ), and a fast response (τ_rise =125 μs and τ_decay =419 μs). Such a lead-free phase transition material combined with semiconductor properties provides a new strategy to develop environmentally friendly multifunctional materials.