Metal Halide Perovskites: From Crystal Formations to Light-Emitting-Diode Applications

Metal halide perovskites (MHPs) are promising light emitters because they have high color purity, high charge-carrier mobility, comparable energy levels with organic semiconductors, and the possibility of diverse crystal forms and various crystal formation methods. Since the first report of MHP lightemitting diodes (PeLEDs) in 2014, many researchers have devoted efforts to increase the luminescence efficiencies of MHPs in various crystal forms, and achieved dramatically improved photoluminescence quantum efficiency of > 90% in MHP emitters and external quantum efficiency of approximate to 14.36% in PeLEDs. Here, the recent progress regarding PeLEDs is reviewed by categorizing MHPs into three types: polycrystalline bulk films, colloidal nanocrystals, and single crystals. The main focus is on photophysical properties, crystallization methods, and mechanisms of various crystal formation, and applications to PeLEDs. Future research directions are also suggested and an outlook for MHP emitters and PeLEDs is given.