Owed to increasing demand for high color-purity displays, there have been various attempts to realize natural colors. In this point of view, light sources with narrow full width half maximums (FWHM) are essentially needed. Metal halide perovskites are a promising alternative emitter material owed to their superior optical properties such as high color-purity (i.e., narrow FWHM <20 nm), solution processability, and low-material cost. Nonetheless, i) small exciton binding energies, ii) long exciton diffusion lengths, and iii) high degree of surface defects induce non-radiative exciton or free carrier dissociation that degrades luminous properties of light-emitting diodes (LEDs).
Here, we report recent developments on methods for controlling optoelectronic properties, and surface defects of metal halide perovskites for high-brightness light-emitting applications. Two-step solution processing techniques have enabled uniform and small sized crystals, which promotes good charge carrier and exciton confinement effects to reduce exciton diffusion lengths and non-radiative recombination in perovskite emitting layers. All-inorganic perovskite nanocrystals were also synthesized to lead better carrier and exciton confinement for high blue electroluminescence. By incorporating yellow-lighting polymer into the perovskite nanocrystals, white LED (CIEx: 0.33, CIEy: 0.34) were fabricated. In addition, intermediate phase engineering of organic-inorganic hybrid metal halide perovskites was used to control crystallization and to passivate surface defects for high-efficiency LEDs.