Stabilizing dynamic surface of highly luminescent perovskite quantum dots for light-emitting diodes

Lead halide perovskite quantum dot (QD) shows great potential for application in light-emitting diodes (LEDs) due to its high photoluminescence quantum yield (PLQY), high exciton binding energy, tunable emission spectra and solution processibility. However, the dynamic binding of conventional organic acid/amine ligands to the QD surface significantly deteriorates its optoelectronic properties and stability, to a large extent affecting the electroluminescence performance of QD-based LEDs. Herein, the zwitterionic molecule, betaine (BET) that could firmly anchor on the QD surface, is introduced to stabilize the dynamic surface and simultaneously passivate the surface defects of QDs. Systematically experimental studies and theoretical calculations reveal that BET-treatment could remove the dynamically bonded OA/OAm ligands and substantially diminish the surface defects of QDs, leading to a boosted PLQY of up to 92 % with improved stability of BET-QDs. Consequently, the electroluminescence performance of green-emitting QD-LEDs was largely improved that the external quantum efficiency was increased to 10.8 %, along with a decreased turn-on voltage of 3.2 V. This work provides new insights into the design criterion of surface ligands for modulating the surface chemistry of perovskite QDs to realize high-performance LEDs or other optoelectronic devices.