Zhang Dongdong, Song Xiaozeng, Gillett Alexander J, Drummond Bluebell H, Jones Saul T E, Li Guomeng, He Hanqing, Cai Minghan, Credgington Dan, Duan Lian
Key Lab of Organic Optoelectronics and Molecular Engineering of Ministry of Education, Department of Chemistry, Tsinghua University, Beijing, 100084, China.
Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, Cambridge, CB3 0HE, UK.
Adv Mater. 2020 May;32(19):e1908355. doi: 10.1002/adma.201908355. Epub 2020 Apr 6.
Multiple donor-acceptor-type carbazole-benzonitrile derivatives that exhibit thermally activated delayed fluorescence (TADF) are the state of the art in efficiency and stability in sky-blue organic light-emitting diodes. However, such a motif still suffers from low reverse intersystem crossing rates (k ) with emission peaks <470 nm. Here, a weak acceptor of cyanophenyl is adopted to replace the stronger cyano one to construct blue emitters with multiple donors and acceptors. Both linear donor-π-donor and acceptor-π-acceptor structures are observed to facilitate delocalized excited states for enhanced mixing between charge-transfer and locally excited states. Consequently, a high k of 2.36 × 10 s with an emission peak of 456 nm and a maximum external quantum efficiency of 22.8% is achieved. When utilizing this material to sensitize a blue multiple-resonance TADF emitter, the corresponding device simultaneously realizes a maximum external quantum efficiency of 32.5%, CIE ≈ 0.12, a full width at half maximum of 29 nm, and a T80 (time to 80% of the initial luminance) of > 60 h at an initial luminance of 1000 cd m .
在天蓝色有机发光二极管中，具有热激活延迟荧光（TADF）特性的多种供体-受体型咔唑-苯腈衍生物在效率和稳定性方面代表了当前的先进水平。然而，这种结构在发射峰<470 nm时仍存在反向系间窜越速率（k）较低的问题。在此，采用氰基苯基这种较弱的受体来取代较强的氰基受体，以构建具有多个供体和受体的蓝色发光体。观察到线性供体-π-供体和受体-π-受体结构都有助于离域激发态，从而增强电荷转移态和局域激发态之间的混合。因此，实现了k为2.36×10 s、发射峰为456 nm以及最大外量子效率为22.8%的结果。当利用这种材料敏化蓝色多共振TADF发光体时，相应器件在初始亮度为1000 cd m时同时实现了32.5%的最大外量子效率、CIE≈0.12、半高宽为29 nm以及>60 h的T80（达到初始亮度80%的时间）。
