Publication date: 15th December 2025
Colloidal quantum dots (QDs) are semiconductor nanoparticles composed of a core/shell/ligand structure. Due to quantum confinement effect, QDs offer color tunability by controlling particle size and possess an excellent color gamut. Owing to these advantages, quantum dot light-emitting diodes (QLEDs), which use QDs as the emission layer (EML), have attracted significant attention as a next-generation display technology. In typical QLEDs, ZnO nanoparticles (NPs) are widely used as an electron transport layer (ETL), as they exhibit high electron mobility, suitable energy level and easy deposition. However, excessively high electron mobility can lead to charge imbalance in the EML. Additionally, oxygen vacancies in ZnO NPs can generate interfacial trap states, promoting non-radiative recombination at the ETL/EML interface and limiting device performance. In this study, we fabricated a stepwise interfacial electronic structure using ZnO/ZnMgO double electron transport layer to improve charge imbalance. The ZnMgO film was deposited on ZnO using RF sputtering, which offers high reproducibility and crystallinity. In this configuration, a solution-processed ZnO layer serves as a buffer ETL that prevents RF sputtering-induced damage and lowers the electron injection barrier. By doping Mg into ZnO, the conduction band level can be tuned and the density of oxygen vacancies can be reduced. The deposition conditions of the ZnMgO layer were systematically optimized by modulating the O2 partial pressure and substrate temperature. Subsequently, their optical characteristics were rigorously analyzed to ensure superior device performance. Consequently, QLEDs with double electron transport layer deposited by RF sputtering exhibited improved performance with a maximum luminance and current efficiency of 142,863 cd/m2 and 26.12 cd/A, which are higher than the devices without ZnMgO. Our results indicate that combining solution-processed ZnO layer with RF-sputtered ZnMgO layer is effective strategy to improve charge balance and reduce non-radiative recombination in QLEDs.
This work was supported by the KEIT (RS-2025-02413057) funded by the Ministry of Trade, Industry & Energy (MOTIE, Korea).
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