Quantum Dot Light-Emitting Diodes with External Quantum Efficiency Exceeding 30% Enabled by a Crown Ether-Modified Electron Transport Layer

Zinc magnesium oxide nanoparticles (ZnMgO NPs), known for their excellent optoelectronic properties, are widely used as the electron transport layer (ETL) in high-performance quantum dot light-emitting diodes (QLEDs). However, their high conductivity and abundant oxygen vacancy defects result in excessive electron injection and exciton quenching at the quantum dot (QD)/ETL interface, which severely limits the device efficiency and stability. In this study, 18-Crown-6, 15-Crown-5, and 12-Crown-4 crown ethers were individually incorporated into the ZnMgO NP system to construct a ZnMgO-Crown ether hybrid ETL. The crown ethers coordinate with Zn²⁺ and Mg²⁺ ions and form hydrogen bonds, stabilizing the metal centers and suppressing the formation of oxygen vacancies. Additionally, crown ether incorporation reduces the surface roughness of ZnMgO NPs, thereby improving the QD/ETL interface and decreasing the nonradiative recombination. Moreover, the crown ether additives modulate the energy band alignment of ZnMgO NPs, increasing the injection barrier at the ETL/cathode interface and reducing electron overflow. As a result, the fabricated QLEDs achieved a peak external quantum efficiency (EQE) of 30.91% and a long T₉₅ lifetime of 6945 h (at 1000 cd/m²). This straightforward strategy offers a viable approach to developing highly efficient and stable QLEDs.