Ligand‐Mediated Surface Carrier Modulation in Perovskite Nanocrystals for Charge‐Symmetric LEDs

Abstract

ABSTRACT Metal halide perovskite nanocrystals (MHP NCs) hold great promise for light‐emitting diodes (LEDs), but face challenges due to weakly‐bound, insulating long‐chain ligands that impede charge transport and compromise stability. We introduce a hydrolysis‐assisted ligand‐exchange strategy that uses a multifunctional π‐conjugated pyridine carboxamide (PCA). This approach replaces native ligands to achieve strong surface binding and to strengthen electrical coupling, while imparting n‐type surface functionalization of MHP NCs. As a result, colloidal stability is improved, trap densities are reduced, and charge balance can be precisely tuned within LEDs. LEDs fabricated using ligand‐exchanged MHP NCs had a current efficiency of 121.4 cd A −1 and an external quantum efficiency of 31.7%, both of which are among the highest reported for green‐emitting LEDs that use MHP NCs. This study demonstrates the ligand‐exchange as a strategic approach for surface functionalization that enables control over charge balance and recombination dynamics, thereby significantly improving the efficiency of LEDs that use MHP NCs.