Su Qiang, Sun Yizhe, Zhang Heng, Chen Shuming
Department of Electrical and Electronic Engineering Southern University of Science and Technology Shenzhen 518055 P. R. China.
Adv Sci (Weinh). 2018 Jul 3;5(10):1800549. doi: 10.1002/advs.201800549. eCollection 2018 Oct.
The phenomenon of positive aging, i.e., efficiency increased with time, is observed in quantum-dot light-emitting diodes (QLEDs). For example, the external quantum efficiency (EQE) of blue QLEDs is significantly improved from 4.93% to 12.97% after storage for 8 d. The origin of such positive aging is thoroughly investigated. The finding indicates that the interfacial reaction between Al cathode and ZnMgO electron transport layer accounts for such improvement. During shelf-aging, the Al slowly reacts with the oxygen from ZnMgO, and consequently, leads to the formation of AlO and the production of oxygen vacancies in ZnMgO. The AlO interlayer reduces the electron injection barrier while the oxygen vacancies increase the conductivity of ZnMgO and, as a result, the electron injection is effectively enhanced. Moreover, the AlO can effectively suppress the quenching of excitons by metal electrode. Due to the enhancement of electron injection and suppression of exciton quenching, the aged blue, green, and red QLEDs exhibit a 2.6-, 1.3-, and 1.25-fold efficiency improvement, respectively. The studies disclose the origin of positive aging and provide a new insight into the exciton quenching mechanisms, which would be useful for further constructing efficient QLED devices.
在量子点发光二极管（QLED）中观察到了正向老化现象，即效率随时间增加。例如，蓝色QLED的外量子效率（EQE）在储存8天后从4.93%显著提高到12.97%。对这种正向老化的起源进行了深入研究。研究结果表明，Al阴极与ZnMgO电子传输层之间的界面反应是这种改善的原因。在储存老化过程中，Al与ZnMgO中的氧缓慢反应，从而导致AlO的形成以及ZnMgO中氧空位的产生。AlO中间层降低了电子注入势垒，而氧空位增加了ZnMgO的电导率，结果有效地增强了电子注入。此外，AlO可以有效地抑制金属电极对激子的猝灭。由于电子注入的增强和激子猝灭的抑制，老化后的蓝色、绿色和红色QLED的效率分别提高了2.6倍、1.3倍和1.25倍。这些研究揭示了正向老化的起源，并为激子猝灭机制提供了新的见解，这将有助于进一步构建高效的QLED器件。
