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Title |
High-efficiency sky blue to ultradeep blue thermally activated delayed fluorescent diodes based on ortho-carbazole-appended triarylboron emitters: above 32% external quantum efficiency in blue devices |
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Author list |
Lee, Young Hoon; Park, Sunghee; Oh, Jihun; Woo, Seung-Je; Kumar, Ajay; Kim, Jang-Joo; Jung, Jaehoon; Yoo, Seunghyup; Lee, Min Hyung |
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Publication date |
2018/09 |
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Citation information |
Advanced Optical Materials, 6, 1800385 (2018) |
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DOI |
10.1002/adom.201800385 |
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Graphical Abstract |
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Abstract |
A novel approach to highly efficient, blue thermally activated delayed fluorescent (TADF) emitters is proposed. A series of ortho-carbazole-appended triarylboron compounds (1-5) are prepared with various substituents, including tert-Bu, Me, and OMe, introduced to the carbazole donor and/or to the dimesitylphenylboron (PhBMes2) acceptor. Depending on the substituents on the donor and/or acceptor moieties, the emission color is finely tuned over the entire blue region from sky blue to ultradeep blue. Retention of a twisted donor (D)-acceptor (A) structure enabled by the ortho D-A connectivity and bulky triarylboron leads to small energy splitting (ΔEST) between singlet and triplet excited states, resulting in very efficient TADF. High?efficiency blue TADF organic light-emitting diodes (OLEDs) are realized by using the proposed ortho D-A compounds as emitters. Among them, the blue OLEDs incorporating a BuCzMeoB (2) emitter exhibit a very high external quantum efficiency (EQE) of 32.8% at Commission Internationale de l'Eclairage (CIE) color coordinates of (0.135, 0.266). The high device efficiency is attributed to both the high photoluminescence quantum yield of 2 in a given host film (93%) and the high horizontal transition dipole ratio (Θ) of 0.76. Ultradeep blue OLEDs with a record?high efficiency are also fabricated with a CzOMeoB (5) emitter, exhibiting an EQE of 14.9% at CIE coordinates of (0.151, 0.058). | |
