Lead‐Free Double Perovskite Semiconductor with Rigid Spacer‐Induced High‐Tc 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)4AgBiBr8 (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 (τrise=125 μs and τdecay=419 μs). Such a lead‐free phase transition material combined with semiconductor properties provides a new strategy to develop environmentally friendly multifunctional materials. Multifunctional material (benzylammonium)4AgBiBr8, which has a step‐like dielectric phase transition at 383 K/387 K (cooling/heating) and excellent photoelectric properties, was obtained by using rigid benzylammonium cations as templates.