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.

Structure and Surface Passivation of Ultrathin Cesium Lead Halide Nanoplatelets Revealed by Multilayer Diffraction

“…While relevant per se , we predict that such insights will become even more significant for the rapidly growing field of self-assembled halide perovskite superstructures, ,,,,− where the methodology we have developed might complement or even outmatch more elaborate characterization tools within the limits imposed by probing a single direction. The Multilayer Diffraction approach we adopted provides indeed a large amount of detailed information, while relying solely on a simple and widely accessible θ:2θ out-of-plane diffraction experiment.…”

“…In such films, the platelet orientation, the interplatelet distance, and the stacking disorder affect the electronic coupling between nanoplatelets, their dielectric screening, and the orientation of their transition dipole moments. Therefore, such parameters can be relevant for tuning the optical characteristics of the device. − …”

Structure and Surface Passivation of Ultrathin Cesium Lead-Halide Nanoplatelets Revealed by Multilayer Diffraction

“…While relevant per se, we predict that such insights will become even more significant for the rapidly growing field of self-assembled halide perovskite superstructures, 5,18,24,25,[55][56][57] where the methodology we have developed might complement or even outmatch more elaborate characterization tools within the limits imposed by probing a single direction. In fact, the Multilayer Diffraction approach we adopted provides a large amount of detailed information while relying solely on a simple and widely accessible θ:2θ out-of-plane diffraction experiment.…”

“…Therefore, such parameters can be relevant for tuning the optical characteristics of the device. [17][18][19] To retrieve all this information, a combination of several techniques is typically required. For example, high-resolution transmission electron microscopy (HR-TEM) is commonly used to investigate the structure of nanoplatelets.…”