Lead-Free Halide Perovskites and Perovskite Variants as Phosphors toward Light-Emitting Applications

Abstract

Lead halide perovskites have attracted tremendous research interests in the light-emitting society owing to their high defect-tolerance, solution-processability, tunable spectrum and efficient emission. In terms of luminescence types, both the narrowband emission derived from free-exciton and broadband white light emission from self-trapped exciton (STE) show great advantages in the light-emitting applications. Despite the fascinating characteristics, their commercialization still suffers from the presence of toxic lead (Pb) and unsatisfactory stability. In this spotlight, we mainly focus on the lead-free candidates as phosphors for possible light-emitting applications. Thanks to the chemical diversity of metal halide perovskites and perovskite variants, many excellent lead-free light-emitting materials have recently been synthesized and characterized. We firstly classify these materials into three types according to material structures, including 1) double perovskites A2B(I)B(III)X6, 2) vacancy ordered perovskites A2B(IV)X6, 3) miscellaneous perovskite variants or halide semiconductors, which refer to halides without clear relation to the perovskite structure. Then we highlight the importance of electronic dimensionality, defects passivation and impurity doping in developing highly efficient perovskite-based emitters. We also discuss their applications in white light emitting diodes (W-LED). Further challenges towards practical applications and potential applications are also included in a section on outlook and future challenges.