Stable Whispering Gallery Mode Lasing from Solution‐Processed Formamidinium Lead Bromide Perovskite Microdisks

Abstract Formamidinium (CH(NH₂)₂, FA) lead halide perovskites exhibit excellent optoelectronic properties for the applications of light‐emitting diodes and lasers. However, the reported formamidinium lead bromide (FAPbBr₃) perovskite‐based lasers mainly depend on the external feedback or Fabry–Pérot mode cavities and suffer from moderate quality (Q) factors. Herein, solution‐processed square and quasi‐circular FAPbBr₃ microdisks are developed to achieve room‐temperature naturally facet‐formed whispering gallery mode (WGM) lasers. These microdisks exhibit relatively high Q factor and tunable laser modes with threshold of 10–70 µJ cm⁻² under 400 nm excitation. Although the synthesized circular microdisk is not regular enough, it still shows higher Q factor of 3455 than that of square microdisk due to the less boundary wave and pesudointegrable leakage. This simple and low‐cost solution processed method can tackle the complicated and expensive conventional preparation techniques of circular microdisks. Power dependent photoluminescence decay transients indicate that the band edge emission of the FAPbBr₃ microdisks originates from free carrier recombination. In addition, these microdisks show high photostability and that room temperature lasing can sustain over 50 min. These results suggest that FAPbBr₃ microdisks can serve as promising WGM lasers with excellent light emission capability and stability toward practical optoelectronic applications.