Tailoring electron transport dynamics via dual-modulation for balanced charge injection in InP QLEDs

Interfacial trap states and charge-transport imbalance at oxide ETL/quantum-dot interfaces remain key limitations in InP-based QLEDs. Here, we propose a dual-modulation strategy that combines ethanolamine (EA) ligand engineering with Mg-doped ZnO (ZnMgO, ZMO) to simultaneously improve the oxide/QD interface and regulate electron transport. EA ligand attachment on ZnO nanoparticles is first confirmed, and its interfacial benefits are identified: XPS O 1s analysis reveals a reduction in oxygen-vacancy-related surface states, while AFM and KPFM measurements show reduced surface roughness and a lowered surface work function, indicating improved film uniformity and interfacial passivation. However, electron-only SCLC analysis reveals that EA treatment also increases the effective electron mobility of ZnO, which can aggravate electron-dominant charge imbalance despite its beneficial passivation effect. To overcome this trade-off, Mg doping is introduced as a transport-modulation route to intentionally suppress excessive electron transport while retaining the interfacial advantages of EA ligands. By systematically tuning the Mg content in EA-ZMO, electron-only current is progressively reduced, confirming controllable moderation of electron transport. Consequently, EA ligand engineering passivates interfacial defects and facilitates electron injection, whereas Mg-content control compensates for the EA-induced mobility enhancement and restores charge balance. The optimized 12.5% EA-ZMO ETL achieves the most balanced charge injection, yielding a peak EQE of 9.23% through coordinated defect passivation and mobility modulation.