Engineering Electron Transport Layer with Ionic Liquid for High-Performance Quantum Dot Light-Emitting Diodes

Zinc oxide nanoparticles (NPs) are currently indispensable electron transport layer (ETL) materials in achieving high-performance quantum dot (QD) light-emitting diodes (QLEDs). However, due to the high conductivity and pervasive surface defects of ZnO NPs, excessive electron injection and exciton quenching at the QD/ETL interface restrain the practical applications of QLEDs. Here, an ionic liquid additive is introduced to construct a hybrid ETL with ZnO NPs. Ionic liquids tend to anchor at the defective sites of ZnO NPs due to electrostatic interactions and hydrogen bonding. This modification improves the surface properties of QDs, optimizing the interface between QDs and ETL, which in turn decreases the probability of nonradiative recombination. Additionally, the additives modulate the energy band structure of ZnO NPs, resulting in a higher barrier at the ETL/cathode interface to decrease the level of electron injection. The resultant QLEDs achieve a high maximum external quantum efficiency (EQE) of 26.71% and a long lifetime (T95@1000 cd m–2) of 5140 h. This straightforward approach offers a viable way to fabricate high-efficiency and long operation-lifetime QLEDs.