Hole-Induced Degradation of ZnMgO and Insights into the Causes of the Limited Electroluminescence Stability of Blue Quantum Dot Light-Emitting Devices

The limited electroluminescence (EL) stability of blue quantum dot light-emitting diodes (B-QLEDs) is currently the main bottleneck preventing their commercialization in display applications. Understanding the degradation mechanism of B-QLEDs is crucial to improving their EL stability. Here, we show that hole leakage into the ZnMgO electron transport layer (ETL) in B-QLEDs can be non-negligible and contribute to limited device stability. Electrical and photoluminescence (PL) measurements, both steady-state and time-resolved PL (TRPL), are used to exclusively examine the effect of holes versus electrons on the ZnMgO layer in specially designed electron-rich or hole-rich devices. Results show that holes induce changes in ZnMgO layers leading to the formation of sub-band gap states in them and a deterioration in their electron injection efficiency. The degraded ZnMgO is also found to negatively affect the photoluminescence quantum yield (PLQY) of the adjacent QDs layer. Electrons in contrast do not have these effects on ZnMgO. Comparative studies on QLEDs in which the ZnMgO layers were previously aged in hole-rich or electron-rich devices show that hole-induced damage in ZnMgO negatively affects QLED efficiency, shedding light on the critical role that hole leakage in B-QLEDs may play in their limited EL stability.