Revealing Relation of Surface Chemical State and Perovskite Quantum‐Dots Electroluminescent Performance

ABSTRACT Although the surface chemical state of perovskite quantum dots (PQDs) is widely acknowledged to govern their electroluminescence (EL), the underlying links and mechanistic origins remain largely unexplored. By designing the purification process, we successfully obtained PQDs with controllable ligand and trap densities, which are the determinant for the surface state. It revealed a correlation between the surface chemistry of PQDs and their EL performance via surface chemical analysis and electrical characterization; specifically, the variations in EL performance originated from the synergistic regulation of ligand density and surface vacancy defects. The former directly influences whether charges can be effectively injected into the emitting layer during device operation, while the latter affects the number of non‐radiative recombination centers and the carrier transport balance. Only controlling the appropriate surface ligand density of PQDs, the light‐emitting diode (LED) achieved high external quantum efficiency (EQE) over 18% without any surface treatment. The surface halogen vacancies of PQDs could be eliminated by halide ligands while maintaining the controllable ligand density, thus the LED achieved a champion EQE of 27.1%, and 5.6‐fold increased operation lifetime.