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

Halide perovskite single crystal of cubic HC(NH2)(2)PbI3 (FAPbI(3)) 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 FAPbI(3) 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 FAPbI(3) perovskite phase, hence achieving a highly stable mixed cation MA(0.45)FA(0.55)PbI(3) perovskite single crystal over a span of 14 months. The MA(0.45)FA(0.55)PbI(3) single crystal exhibits exceptional optoelectronic properties like high carrier mobility of 271 +/- 60 cm(2) s(-1) V-1 and long diffusion length up to 254 mu m, which are twice the values for sole MAPbI(3) or FAPbI(3) crystals. In addition, the photodetector based on MA(0.45)FA(0.55P)bI(3) single crystal exhibits low detection limit of about 1 nW cm(-2), high ON-OFF ratio of similar to 1000, short response time of less than 200 mu s, and impressive stability under aging in dark for 4 months or continuous photo-switching test for 1000 s.