(Benzimidazolium)2GeI4: A layered two-dimensional perovskite with dielectric switching and broadband near-infrared photoluminescence

Two-dimensional (2D) lead halide perovskites have attracted tremendous attention due to their outstanding physical properties. However, the presence of toxic lead is a major problem for large-scale applications. Here, we report the synthesis, phase transition, dielectric and photoluminescence (PL) properties of a lead-free two-dimensional Ge-based perovskite (BIM)2GeI4 (BIM = benzimidazolium). Variable temperature single crystal X-ray diffraction experiment and differential scanning calorimeter measurement reveal that (BIM)2GeI4 experiences a phase transition at 405 K, accompanying by the order-disorder change of organic spacer. Moreover, the step-like dielectric transition near phase transition makes it suitable for dielectric switching. Meanwhile, (BIM)2GeI4 has a direct bandgap of 2.23 eV and broadband emission from 550 nm to 1000 nm, implying their unique optical property for potential near-infrared lighting and displaying. This work provides a fresh example for the development of lead-free 2D Ge-based perovskite with potential application in the fields of optoelectronics and high temperature dielectric switching.