2, Pohang University of Science and Technology, Pohang, , Korea (the Republic of)
Lead halide perovskites have been used as emission layers in perovskite light-emitting diodes (PeLEDs), and have many advantages such as high charge-carrier mobility, solution processability, high color purity, color tunability and low material cost. However, low electroluminescence (EL) efficiency of PeLEDs at room temperature is a challenge that must be overcome. Here, we present high-efficiency PeLEDs by controlling the dimension and dimensionality (D) of perovskite grains/crystals to overcome the EL efficiency limitations. First, we kinetically control the grain size in 3D bulk polycrystalline films and achieve uniform methylammonium lead bromide (MAPbBr3) and CsPbBr3 films with reduced grain size. By using fine stoichiometry control, additive-based nanocrystal pinning and ideal buffer layer, we prevent the formation of strong luminescence quenchers (metallic Pb atoms), suppress the non-radiative recombination of charge carriers at the interfaces and in the emitting layers, and achieve high external quantum efficiency (11.7%) in PeLEDs based on 3D perovskite bulk films. High-efficiency flexible MAPbBr3 PeLEDs based on graphene anode and polymeric anode are also first developed. We also develop efficient quasi-2D (Ruddlesden-Popper phase) bulk polycrystalline films with improved film morphology, exciton confinement and reduced trap density, and then demonstrate efficient PeLEDs based on them. Furthermore, by synthesizing ligand-engineered colloidal perovskite 0D nanoparticles (NPs) with high photoluminescence quantum efficiency, we fabricate high-efficiency PeLEDs based on MAPbBr3 and formaminidium lead bromide NPs. The effects of ligand engineering on photo-physical and surface-chemical properties of perovskite NPs, and EL efficiencies of PeLEDs are also systematically studied.