He Yanmei, Qiao Zhenyang, Cai Xinyi, Li Mengke, Li Wei, Xie Wentao, Qiu Weidong, Wang Liangying, Su Shi-Jian
State Key Laboratory of Luminescent Materials and Devices and Institute of Polymer Optoelectronic Materials and Devices, South China University of Technology, Wushan Road 381, Guangzhou 510640, Guangdong Province, P. R. China.
ACS Appl Mater Interfaces. 2020 Nov 4;12(44):49905-49914. doi: 10.1021/acsami.0c14123. Epub 2020 Oct 20.
Versatile host materials with good chemical stability and carrier-transporting ability are quite responsible for achieving stable solution-processed thermally activated delayed fluorescence (TADF) organic light-emitting diodes (OLEDs). Herein, we reported three bipolar dendritic hosts with or without the electron-withdrawing pyridine moiety via 6-site-linkages, namely, 3,3'-bis(3,3″,6,6″-tetra--butyl-9'-[9,3':6',9″-tercarbazol]-9'-yl)-1,1'-biphenyl (mCDtCBP), 3,3″,6,6″-tetra--butyl-9'-(6-(3-(3,3″,6,6″-tetra--butyl-9'-[9,3':6',9″-tercarbazol]-9'-yl)phenyl)pyridine-2-yl)-9'-9,3':6',9″-tercarbazole (mCDtCBPy), and 6,6'-bis(3,3″,6,6″-tetra--butyl-9'-[9,3':6',9″-tercarbazol]-9'-yl)-2,2'-bipyridine (mCDtCBDPy), exhibiting outstanding solubility, thermal stability as well as electrochemical stability. According to the calculation of bond dissociation energy (BDE), photodegradation results, and carrier dynamics evaluation, a significant relationship between device stability and the pyridine-based dendritic hosts was uncovered. Using mCDtCDPy with the highest electron mobility as the host, the solution-processed bluish-green TADF-OLED showed the shortest operational lifetime due to the unbalanced charge fluxes despite its highest anionic BDE for good chemical stability. However, the device based on mCDtCBPy exhibited twice longer lifetime than that based on mCDtCBP in spite of their similar balanced charge transportation, highlighting the importance of higher anionic BDE of the C-N bond in the device degradation process. Our findings unveiled a potential approach to achieve a subtle regulation of chemical stability and carrier transportation for realizing stable solution-processed TADF-OLEDs.
具有良好化学稳定性和载流子传输能力的多功能主体材料对于实现稳定的溶液法制备的热激活延迟荧光（TADF）有机发光二极管（OLED）至关重要。在此，我们报道了三种通过6位点连接带有或不带有吸电子吡啶部分的双极树枝状主体，即3,3'-双(3,3″,6,6″-四叔丁基-9'-[9,3':6',9″-三联咔唑]-9'-基)-1,1'-联苯（mCDtCBP）、3,3″,6,6″-四叔丁基-9'-(6-(3-(3,3″,6,6″-四叔丁基-9'-[9,3':6',9″-三联咔唑]-9'-基)phenyl)吡啶-2-基)-9'-9,3':6',9″-三联咔唑（mCDtCBPy）和6,6'-双(3,3″,6,6″-四叔丁基-9'-[9,3':6',9″-三联咔唑]-9'-基)-2,2'-联吡啶（mCDtCBDPy），它们表现出出色的溶解性、热稳定性以及电化学稳定性。根据键解离能（BDE）的计算、光降解结果和载流子动力学评估，发现了器件稳定性与基于吡啶的树枝状主体之间的显著关系。使用具有最高电子迁移率的mCDtCDPy作为主体，溶液法制备的蓝绿色TADF-OLED尽管具有良好化学稳定性的最高阴离子BDE，但由于电荷通量不平衡，其工作寿命最短。然而，基于mCDtCBPy的器件尽管其电荷传输平衡相似，但寿命比基于mCDtCBP的器件长两倍，突出了C-N键较高的阴离子BDE在器件降解过程中的重要性。我们的研究结果揭示了一种潜在的方法，可实现对化学稳定性和载流子传输的精细调控，以实现稳定的溶液法制备的TADF-OLED。
