Unveiling the TADF emitters with apparent negative singlet-triplet gaps : implications for exciton harvesting and OLED performance
Abstract
Intramolecular through-space charge transfer thermally activated delayed fluorescence (TSCT-TADF) has attracted much attention recently as it can achieve both small energy splitting and high emission efficiency. However, the relationship of excited states between TSCT and through-bond charge transfer (TBCT) remains a challenge in the TSCT-TADF molecules. Herein, three compounds DPS-m-bAc, DPS-p-bAc, and DPS-OAc that possess emissive TSCT and/or TBCT states are prepared. Interestingly, a so-called inverted energy gap is found for both DPS-m-bAc and DPS-p-bAc in toluene solution, which results from the different charge transfer states of ICThigh and ICTlow, as proved by the detailed transient photoluminescence and calculated results. Intense emission from blue to yellow associated with high photoluminescence quantum yields of 70–100% are measured in doped polymethyl(methacrylate) (PMMA) films. Notably, compound DPS-m-bAc achieves the highest reverse intersystem crossing rate constant (kRISC) of over 107 s−1 in a PMMA film, benefiting from close-lying TSCT and TBCT states. The solution-processed device with DPS-m-bAc displays a maximum external quantum efficiency of 21.7% and a relatively small efficiency roll-off (EQE of 20.2% @ 100 cd m−2). Overall, this work demonstrates how with judicious emitter engineering, a synergy between different charge transfer excited states, can be achieved, providing an avenue to achieve highly efficient solution-processed OLEDs.
Citation
Chen , X , Bagnich , S , Pollice , R , Li , B , Zhu , Y , Saxena , R , Yin , Y , Zhu , W , Aspuru-Guzik , A , Zysman-Colman , E , Köhler , A & Wang , Y 2023 , ' Unveiling the TADF emitters with apparent negative singlet-triplet gaps : implications for exciton harvesting and OLED performance ' , Advanced Optical Materials , vol. Early View , 2301784 . https://doi.org/10.1002/adom.202301784
Publication
Advanced Optical Materials
Status
Peer reviewed
ISSN
2195-1071Type
Journal article
Rights
Copyright © 2023 the Authors. This work has been made available online in accordance with the University of St Andrews Open Access policy. This accepted manuscript is distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. The final published version of this work is available at https://doi.org/10.1002/adom.202301784
Description
Financial support was from the National Natural Science Foundation of China (Nos. 22371020, 52073035) and the Special program for foreign talents in Changzhou City (CQ20224052). R.P. acknowledges funding through a Postdoc. Mobility fellowship by the Swiss National Science Foundation (SNSF, Project No. 191127). A.A.-G. thanks Dr. Anders G. Frøseth for his generous support. A.A.-G. also acknowledges the generous support of Natural Resources Canada and the Canada 150 Research Chairs program. A.K., S.B., and R.S. acknowledge funding from the Deutsche Forschungsgemeinschaft (KO 3973/8-1) and through the EU HORIZON-MSCA-2021-DN TADF solutions, project number 101073045. E.Z.-C. acknowledges support from the Engineering and Physical Sciences Research Council (EP/W015137/1 and EP/X026175/1).Collections
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