Two-Dimensional Nanoplatelet Superlattices Overcoming Light Outcoupling Efficiency Limit in Perovskite Quantum Dot Light-Emitting Diodes

Abstract Quantum dot (QD) light-emitting diodes (LEDs) are emerging as one of the most promising candidates for next-generation displays. However, their intrinsic light outcoupling efficiency remains considerably lower than the organic counterpart, because it is not yet possible to control the transition-dipole-moment (TDM) orientation in QD solids at device level. Here, using the colloidal lead halide perovskite nanoplatelets (NPLs) as a model system, we report a directed self-assembly approach to form the two-dimensional superlattices (2DSLs) with the out-of-plane vector perpendicular to the substrate plane. The ligand and substrate engineering yields close-packed planar arrays with the side faces linked to each other. Emission polarization in individual NPLs rescales the radiation from horizontal and vertical transition dipoles, effectively resulting in preferentially horizontal TDM orientation. Based on the emissive thin films comprised of stacks of 2D superlattices, we demonstrate an enhanced ratio of horizontal dipole as revealed by 2D k-space spectroscopy. Our optimized single-junction QD LEDs showed peak external quantum efficiency of up to 24% and power efficiency exceeding 110 lm W -1 , comparable to state-of-the-art organic LEDs.