Department of Electrical and Computer Engineering and Waterloo Institute for Nanotechnology, University of Waterloo, 200 University Avenue West, Waterloo, Ontario N2L 3G1, Canada.
Nanoscale. 2018 Feb 1;10(5):2623-2631. doi: 10.1039/c7nr07683e.
Although the use of polyethylenimine (PEI) in quantum dot light-emitting devices (QDLEDs) has recently been found to improve efficiency, the mechanism behind this increase has been disputed in the literature. In this work, we conduct investigations to elucidate the role of PEI in enhancing QDLED efficiency. Spectroscopic studies of devices with a phosphorescent marking layer reveal that the PEI layer increases, rather than decreases, the generation of excitons within the hole transporting layer indicative of increased electron injection. Delayed electroluminescence measurements corroborate these findings as devices with a PEI interlayer exhibit a greater concentration of excess mobile and trapped electrons. We attribute the improvement in efficiency despite the ensuing increased charge imbalance within the devices to the passivation of exciton quenching at the ZnO/QD interface. The increase in efficiency predominantly occurs over low driving currents which is particularly attractive for the brightness targets of display applications. Furthermore, despite the increased charge imbalance, the PEI passivation layer appears to have little effect on QDLED stability. This shows that excess electrons and Auger quenching by unneutralized electrons are not detrimental to QDLED stability.
尽管最近发现使用聚乙烯亚胺 (PEI) 可以提高量子点发光器件 (QDLED) 的效率，但文献中对这种提高的机制存在争议。在这项工作中，我们进行了研究，以阐明 PEI 在提高 QDLED 效率方面的作用。对具有磷光标记层的器件进行的光谱研究表明，PEI 层增加了空穴传输层内激子的产生，而不是减少了激子的产生，这表明电子注入增加了。延迟电致发光测量证实了这些发现，因为具有 PEI 层的器件表现出更多的过剩可动和俘获电子浓度。尽管器件内部的电荷不平衡增加，但我们认为效率的提高归因于在 ZnO/QD 界面处的激子猝灭的钝化。效率的提高主要发生在低驱动电流下，这对于显示应用的亮度目标特别有吸引力。此外，尽管电荷不平衡增加，但 PEI 钝化层似乎对 QDLED 的稳定性几乎没有影响。这表明过量电子和未中和电子的俄歇猝灭对 QDLED 的稳定性没有不利影响。
