Yoon Jiwon, Kim Seong Keun, Kim Hyung Jong, Choi Suna, Jung Sang Won, Lee Hyuna, Kim Jun Yun, Yoon Dae-Wi, Han Chang Wook, Chae Weon-Sik, Kwon Jang Hyuk, Cho Min Ju, Choi Dong Hoon
Department of Chemistry, Research Institute for Natural Sciences, Institution Korea University, 145, Anam-ro, Sungbuk-gu, Seoul, 02841, Republic of Korea.
Department of Information Display, Kyung Hee University, 26, Kyungheedae-ro, Dongdaemun-gu, Seoul, 02447, Republic of Korea.
Chemistry. 2020 Dec 9;26(69):16383-16391. doi: 10.1002/chem.202002655. Epub 2020 Oct 27.
In this study, two host materials, pCzBzbCz and pCzPybCz, are synthesized to achieve a high efficiency and long lifetime of blue thermally activated delayed fluorescence organic light-emitting diodes (TADF-OLEDs). The molecular design strategy involves the introduction of a pyridine group into the core structure of pCzPybCz as an electron-withdrawing unit, and an electron-donating phenyl group into the structure of pCzBzbCz. These host materials demonstrate good thermal stability and high triplet energy (T =3.07 eV for pCzBzbCz and 3.06 eV for pCzPybCz) for the fabrication of blue TADF-OLEDs. In particular, pCzPybCz-based OLED devices demonstrate an external quantum efficiency (EQE) of 22.7 % and an operational lifetime of 24 h (LT , time to attain 90 % of initial luminance) at an initial luminance of 1000 cd m . This superior lifetime could be explained by the C-N bond dissociation energy (BDE) in the host molecular structure. Furthermore, a mixed-host system using the electron-deficient 2,4-bis(dibenzo[b,d]furan-2-yl)-6-phenyl-1,3,5-triazine (DDBFT) is proposed to inhibit the formation of the anion state of our host materials. In short, the device operational lifetime is further improved by applying DDBFT. The carbazole-based asymmetric host molecule containing a pyridine core realizes a high-efficiency blue TADF-OLED showing a positive effect on the operating lifetime, and can provide useful strategies for designing new host materials.
在本研究中，合成了两种主体材料pCzBzbCz和pCzPybCz，以实现高效且长寿命的蓝色热激活延迟荧光有机发光二极管（TADF - OLED）。分子设计策略包括将吡啶基团作为吸电子单元引入pCzPybCz的核心结构中，并将供电子苯基引入pCzBzbCz的结构中。这些主体材料表现出良好的热稳定性和较高的三线态能量（pCzBzbCz的T = 3.07 eV，pCzPybCz的T = 3.06 eV），适用于制造蓝色TADF - OLED。特别是，基于pCzPybCz的OLED器件在初始亮度为1000 cd·m⁻²时，展现出22.7%的外量子效率（EQE）和24小时的工作寿命（LT，达到初始亮度90%的时间）。这种优异的寿命可以通过主体分子结构中的C - N键解离能（BDE）来解释。此外，提出了一种使用缺电子的2,4 - 双（二苯并[b,d]呋喃 - 2 - 基）- 6 - 苯基 - 1,3,5 - 三嗪（DDBFT）的混合主体系统，以抑制我们主体材料的阴离子态形成。简而言之，通过应用DDBFT进一步提高了器件的工作寿命。含有吡啶核心的咔唑基不对称主体分子实现了高效蓝色TADF - OLED，对工作寿命有积极影响，并可为设计新型主体材料提供有用策略。
