Achieving balanced charge transport is crucial for high-performance quantum-dot light-emitting diodes (QLEDs), yet it remains a significant challenge. This issue is notably evident when using high-mobility metal oxides, such as ZnO and SnO2 nanoparticles, as electron transport layers (ETLs), due to their excessive electron mobility which leads to a severe mismatch with most organic hole transport layers (HTLs). Consequently, the balanced charge injection and high efficiency in conventional QLEDs has been largely confined to high-mobility HTLs like poly(9,9-dioctyl-fluorene-co-N-(4-butylphenyl) diphenylamine) (TFB). In this study, we present a universal strategy to precisely tune the electron mobility of SnO2 nanocrystals through controlled Zn2+ doping concentration. This approach enables synergistic matching with a range of commonly used HTLs, achieving a near-ideal charge balance across all systems. As a result, we fabricated high-performance QLEDs with universal HTL compatibility, where all optimized devices exhibited a maximum external quantum efficiency (EQE) exceeding 27%. Importantly, the positive aging effect commonly observed in ZnMgO-based devices is completely eliminated in all our SnO2-based QLEDs. This work provides a general and universal ETL materials for fabricating highly efficient and stable QLEDs compatible with diverse hole transport materials without the need to consider their hole mobility.
Liu et al. (2026) studied this question.