A formamidinium–methylammonium lead iodide perovskite single crystal exhibiting exceptional optoelectronic properties and long-term stability

Abstract

Halide perovskite single crystal of cubic HC(NH₂)₂PbI₃ (FAPbI₃) having excellent optoelectronic properties, such as narrow bandgap, large absorption coefficient and superior thermal stability has caught a surge of attention as a promising material for production of high-performance optoelectronic devices. However, at room temperature, the self-transformation of cubic FAPbI₃ perovskite phase to non-perovskite phase leaves a critical roadblock to its practical viability. Herein, a simple alloying strategy by mixing methylammonium with formamidinium is developed to stabilize the FAPbI₃ perovskite phase, hence achieving a highly stable mixed cation MA_0.45FA_0.55PbI₃ perovskite single crystal over a span of 14 months. The MA_0.45FA_0.55PbI₃ single crystal exhibits exceptional optoelectronic properties like high carrier mobility of 271 ± 60 cm² s⁻¹ V⁻¹ and long diffusion length up to 254 μm, which are twice the values for sole MAPbI₃ or FAPbI₃ crystals. In addition, the photodetector based on MA_0.45FA_0.55PbI₃ single crystal exhibits low detection limit of about 1 nW cm⁻², high ON–OFF ratio of ∼1000, short response time of less than 200 μs, and impressive stability under aging in dark for 4 months or continuous photo-switching test for 1000 s.