2000102 (1 of 10) © 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.advopticalmat.de FULL PAPER Rigid Oxygen-Bridged Boron-Based Blue Thermally Activated Delayed Fluorescence Emitter for Organic Light-Emitting Diode: Approach towards Satisfying High Efciency and Long Lifetime Together Dae Hyun Ahn, Jee Hyun Maeng, Hyuna Lee, Hanjong Yoo, Raju Lampande, Ju Young Lee,* and Jang Hyuk Kwon* DOI: 10.1002/adom.202000102 intersystem crossing (RISC) from the lowest triplet excited state (T 1 ) to the lowest singlet excited state (S 1 ) and also cost-efective by the use of inexpensive pure organic chemicals. [1–5] However, blue TADF OLEDs show a short operational lifetime due to numerous parameters. [6,7] Normally, the long-delayed exciton decay lifetime of the TADF emitter is one of the main causes of the degradation of TADF OLEDs. Especially, in blue devices, long- lived high energy of triplet excitons can provide a critical degradation to the TADF materials. [8,9] In addition, efcient TADF materials have highly twisted confgura- tion between electron-donor and acceptor units to achieve small ΔE ST by reducing the spatial overlap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). [1,10,11] Generally, the C–N bond between donor and acceptor moieties is weaker than the C–C bond and simulta- neously causes the low bond dissociation energy (BDE). [12,13] On the other hand, blue TADF emitters have high T 1 , resulting in the utilization of phosphine oxide-based host materials such as bis[2-(diphenylphosphino)phenyl] ether oxide (DPEPO) and dibenzo[b,d]furan-2,8-diylbis(diphenylphosphine oxide) (DBFPO) due to their high T 1 values. [14,15] However, such phos- phine oxide-based host materials show low operational stability because of their very low BDE. [16,17] Unfortunately, phosphine oxide free materials have relatively low T 1 , therefore there are very limited host materials available that could confne triplet energy to the deep-blue TADF emitter. To overcome these limitations, fewer studies have been reported on the long operational lifetime of blue TADF- OLEDs. [18–22] S. G. Ihn et al. reported indolocarbazole and pyrimidine-based TADF emitter, 5,8-bis(4-(2,6-diphenylpy- rimidin-4-yl)phenyl)-5,8-dihydroindolo[2,3-c]carbazole (BDpyInCz) with a long-delayed exciton lifetime of 32 μs. [18] However, their device exhibited a low external quantum ef- ciency (EQE) (12%) and device lifetime (LT 80 ) of only 8 h at the ini- tial luminance of 500 cd m -2 with deep-blue color coordinates Thermally activated delayed fuorescence (TADF) materials have emerged as an efcient emitter for achieving high efciency of blue organic light emitting diodes (OLEDs). However, it is challenging to satisfy both high device ef- ciency and long operational lifetime together. Here, highly efcient and elec- trochemically stable blue TADF emitter, 5-(5,9-dioxa-13b-boranaphtho[3,2,1-de] anthracen-7-yl)-10,15-diphenyl-10,15-dihydro-5H-diindolo[3,2-a:3′,2′-c]carbazole (DBA-DI) is designed and synthesized for high efciency and long lifetime OLED. This emitter exhibits high photoluminescence quantum yield of 95.3%, small single-triplet energy gap of 0.03 eV, short delayed exciton lifetime of 1.25 μs, and high bond dissociation energy (BDE). Also, phosphine oxide free high triplet energy host systems (single and mixed) and exciton blocking layer materials are analyzed using molecular and optical simulations to fnd an efcient host system with high BDE and suitable emission zone for high efciency and stable OLEDs. The fabricated OLED with DBA-DI and high triplet host exhibited a maximum external quantum efciency (EQE) of 28.1% with blue CIE color coordinates of (0.16, 0.39) and long operational lifetime (LT 50 ) of 329 h at the initial luminance of 1000 cd m -2 . Furthermore, the mixed host-based TADF device showed a slightly lower EQE of 26.4% and almost two times longer lifetime (LT 50 : 540 h) than the single host device. D. H. Ahn, J. H. Maeng, H. Lee, H. Yoo, Dr. R. Lampande, Prof. J. Y. Lee, Prof. J. H. Kwon Organic Optoelectronic Device Lab (OODL) Department of Information Display Kyung Hee University 26 Kyungheedae-ro, Dongdaemun-gu, Seoul 02447, Republic of Korea E-mail: juyoung105@khu.ac.kr; jhkwon@khu.ac.kr The ORCID identifcation number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adom.202000102. 1. Introduction Blue organic light-emitting diodes (OLEDs) utilizing ther- mally activated delayed fuorescence (TADF) are promising for the next-generation display and lighting technology due to their high efciency. Generally, TADF materials are highly efcient because of the utilization of triplet excitons by reverse Adv. Optical Mater. 2020, 8, 2000102 21951071, 2020, 11, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/adom.202000102 by Kyung Hee University Library, Wiley Online Library on [19/12/2022]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License