(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 2D Ge-based perovskite (BIM)₂GeI₄ (BIM = benzimidazolium) which experiences a phase transition at 405 K accompanied by an order-disorder change of organic spacer. Moreover, the step-like dielectric transition near the phase transition temperature makes it suitable for dielectric switching. Meanwhile, (BIM)₂GeI₄ has a direct bandgap of 2.23 eV and broadband emission from 550 to 1000 nm, implying its 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 applications in the fields of optoelectronics and high temperature dielectric switching.