Complementary Triple-Ligand Engineering Approach to Methylamine Lead Bromide Nanocrystals for High-Performance Light-Emitting Diodes

Abstract

Conjugated and short-molecule capping ligands have been demonstrated as a valid strategy for achieving high-efficiency perovskite nanocrystal (NCs) light-emitting diodes (LEDs) owing to their advantage of allowing efficient carrier transport between NCs. However, monotonously utilizing conjugated ligands cannot achieve sufficient surface modification/passivation for perovskite NCs, leading to their poor photoluminescence quantum yield (PLQY) and dispersibility. This work designs a complementary ligand synthesis method to obtain high-quality methylamine lead bromide (MAPbBr₃) NCs and then leverage them into efficient LEDs. The complementary ligand system combines a conjugated ligand 3-phenyl-2-propen-1-amine (PPA) and a long-chain ligand didodecyldimethylammonium bromide (DDAB) together with a well-known inductive inorganic ligand ZnBr₂. With such complementary ligand engineering, we significantly improve the emissive features of MAPbBr₃ NCs (PLQY: 99% ± 0.7%). Simultaneously, the complementary ligand strategy facilitated the adequate charge transportation in related NCs films and modified the interfacial energy-level alignment when the NCs assemble as an emitting layer into LEDs. Finally, based on this NCs synthesis method, high-efficiency green LEDs were achieved, exhibiting the maximum luminance of 1.59 × 10⁴ cd m^-2, a current efficiency of 23.7 cd A^-1, and an external quantum efficiency of 7.8%. Our finding could provide a new avenue for further development of LEDs and their commercial application.

Keywords: complementary ligands; light-emitting diodes; methylammonium lead bromide; perovskite nanocrystals; surface passivation.