Shen Qibin, Hao Yanlei, Ma Luying, Wang Xiaoyu
Department of Physics and State Key Laboratory of Silicon Materials, Zhejiang University, Hangzhou 310027, China.
Center for Chemistry of High-Performance and Novel Materials, State Key Laboratory of Silicon Materials, Department of Chemistry, Zhejiang University, Hangzhou 310027, China.
J Phys Chem Lett. 2021 Jul 29;12(29):7019-7025. doi: 10.1021/acs.jpclett.1c01560. Epub 2021 Jul 21.
To understand the electronic processes in quantum-dot light-emitting diodes (QLEDs), a comparative study was performed by time-resolved transient electroluminescence (TREL). We fabricated red, green, and blue (R-, G-, and B-) QLEDs with poly(9,9-dioctylfluorene---(4--butylphenyl)diphenylamine) as the hole-transporting layer with conventional structures. The external quantum efficiency (EQE) and current efficiency were 19.2% and 22.7 cd A for R-QLEDs, 21.1% and 93.3 cd A for G-QLEDs, and 10.6% and 10.4 cd A for B-QLEDs, respectively. The TREL results for B-QLEDs were remarkably different from those for R- and G-QLEDs because of the insufficient electron injection crossing the type II heterojunction between the emission layer and the electron-transporting layer. We further applied poly(-vinylcarbazole) as the hole-transporting layer and obtained much better performance for B-QLEDs, with EQE and current efficiency of 15.9% and 15.4 cd A, respectively. Concomitant with the increase in EQE are an increase in the turn-on voltage from 2.3 to 3.7 V and a transient electroluminescence spike after voltage turn-off.
为了理解量子点发光二极管（QLED）中的电子过程，通过时间分辨瞬态电致发光（TREL）进行了一项对比研究。我们采用传统结构，以聚（9,9-二辛基芴-（4-丁基苯基）二苯胺）作为空穴传输层，制备了红色、绿色和蓝色（R-、G-和B-）QLED。R-QLED的外量子效率（EQE）和电流效率分别为19.2%和22.7 cd/A，G-QLED分别为21.1%和93.3 cd/A，B-QLED分别为10.6%和10.4 cd/A。由于电子注入不足，无法穿过发射层与电子传输层之间的II型异质结，B-QLED的TREL结果与R-和G-QLED的结果显著不同。我们进一步应用聚（乙烯基咔唑）作为空穴传输层，B-QLED的性能有了显著提升，EQE和电流效率分别为15.9%和15.4 cd/A。随着EQE的增加，开启电压从2.3 V增加到3.7 V，并且在电压关闭后出现瞬态电致发光尖峰。
