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Managing local triplet excited states of boron-based TADF emitters for fast spin-flip process: Toward highly efficient TADF-OLEDs with low efficiency roll-off

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Abstract
Improving the rate of a spin-flip process from a triplet to a singlet excited state, which is known as reverse intersystem crossing (RISC), is a challenging issue in realizing efficient and stable organic light-emitting diodes based on thermally activated delayed fluorescence (TADF-OLEDs). Herein, we report two donor-acceptor-type TADF emitters (TMCzBCO and DMACBCO) employing a boron-carbonyl (BCO) hybrid acceptor unit. The emitters possess a (3)n pi* state of the BCO unit as an intermediate local triplet excited state ((LE)-L-3, T-2), leading to the large spin-orbit coupling between the T-2 and excited singlet (S-1) states with significantly low activation barriers <10 meV. Thus, a fast RISC with rate constants (k(RICS)) exceeding 10(6) s(-1), as well as short exciton lifetimes (similar to 1 mu s), are realized. Using the TADF emitters, high-performance TADF-OLEDs with maximum external quantum efficiencies of 24.7% for the green (TMCzBCO) and 28.4% for the yellow (DMACBCO) are presented. Remarkably, the devices sufficiently maintain high efficiency at high luminance, exceeding 20% at 5,000 cd m(-2) and 18% at 10,000 cd m(-2). These results indicate the crucial role of the (3)n pi* state of BCO in the improvement of the RISC rate and shortening of the exciton lifetime, enhancing the optoelectrical performance of TADF-OLEDs.
Author(s)
이영훈신윤섭이태환정재훈이정환이민형
Issued Date
2021
Type
Article
Keyword
Thermally activated delayed fluorescenceOLEDsFast spin-flipBoron acceptorCarbonyl
DOI
10.1016/j.cej.2021.130224
URI
https://oak.ulsan.ac.kr/handle/2021.oak/9658
https://ulsan-primo.hosted.exlibrisgroup.com/primo-explore/fulldisplay?docid=TN_cdi_gale_infotracacademiconefile_A669725615&amp;context=PC&amp;vid=ULSAN&amp;lang=ko_KR&amp;search_scope=default_scope&amp;adaptor=primo_central_multiple_fe&amp;tab=default_tab&amp;query=any,contains,Managing%20local%20triplet%20excited%20states%20of%20boron-based%20TADF%20emitters%20for%20fast%20spin-flip%20process:%20Toward%20highly%20efficient%20TADF-OLEDs%20with%20low%20efficiency%20roll-off&amp;offset=0&amp;pcAvailability=true
Publisher
CHEMICAL ENGINEERING JOURNAL
Location
네덜란드
Language
영어
ISSN
1385-8947
Citation Volume
423
Citation Number
1
Citation Start Page
130224
Citation End Page
130224
Appears in Collections:
Natural Science > Chemistry
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