Zn<SUB>0.9</SUB>Mg<SUB>0.1</SUB>O nanoparticles (NPs) were employed as electron transport layers (ETLs) with varying thickness, and the effects thereof on the efficiency of top-emission quantum dot light-emitting diodes (TE-QLEDs) fabricated inside a bank were investigated. Increasing the thickness of the Zn<SUB>0.9</SUB>Mg<SUB>0.1</SUB>O NP ETL led to reduction in oxygen vacancies, resulting in decreased conductivity and current density of the TE-QLEDs. This reduction in conductivity was confirmed by electron-only device (EOD) characterization. At a Zn<SUB>0.9</SUB>Mg<SUB>0.1</SUB>O NP ETL thickness of 30 nm, the hydroxide oxygen concentration reached a minimal, minimizing exciton quenching at the quantum dot (QD) and Zn<SUB>0.9</SUB>Mg<SUB>0.1</SUB>O NP ETL interface and thus enhancing the QD charge balance, significantly improving TEQLED efficiency. A TE-QLED with a 30-nm-thick Zn<SUB>0.9</SUB>Mg<SUB>0.1</SUB>O NP ETL exhibited outstanding performance, with a maximum current efficiency of 90.92 cd/A and a top external quantum efficiency of 21.66%. These findings underscore the critical role of Zn<SUB>0.9</SUB>Mg<SUB>0.1</SUB>O NP ETL thickness in suppressing exciton quenching and optimizing charge balance for enhanced TE-QLED performance.