Reducing efficiency roll-off in multi-resonant thermally activated delayed fluorescent OLEDs through modulation of the energy of the T2 state
Abstract
The S1 state and high-lying triplet excited states (ΔES1Tn) offer insight into clarifying the mechanism of efficiency roll-off of organic light-emitting diodes (OLEDs). However, experimental detection of the ΔES1Tn is challenging due to Kasha's rule. Here, two emitters, PhCz-O-DiKTa and PhCz-DiKTa , showing multi-resonant thermally activated delayed fluorescence (MR-TADF) are reported. By modulating the conjugation between the MR-TADF DiKTa emissive center and donor substituent, emission directly from the T2 state is for the first time observed in MR-TADF emitters. Single crystal and reduced density gradient analyses reveal the origin of the reduced observed concentration-quenching results from weak CH···π and slipped π···π stacking interactions, which suppress nonradiative transitions. Theoretical and photophysical investigations reveal that the ΔES1T2 difference influences the reverse intersystem crossing rate. The OLEDs employing PhCz-O-DiKTa and PhCz-DiKTa as emitters show maximum external quantum efficiencies (EQEmax) of over 20%, but very different efficiency roll-off behavior (54.5% vs 13.6% at 100 cd m−2). Thus, this design provides a possible solution to mitigating device efficiency roll-off by designing MR-TADF emitters with degenerate S1 and T2 states.
Citation
Wang , T , Gupta , A K , Cordes , D B , Slawin , A M Z & Zysman-Colman , E 2023 , ' Reducing efficiency roll-off in multi-resonant thermally activated delayed fluorescent OLEDs through modulation of the energy of the T 2 state ' , Advanced Optical Materials , vol. 11 , no. 10 , 2300114 . https://doi.org/10.1002/adom.202300114
Publication
Advanced Optical Materials
Status
Peer reviewed
ISSN
2195-1071Type
Journal article
Rights
Copyright © 2023 The Authors. Advanced Optical Materials published by Wiley-VCH GmbH. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Description
Funding: This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska Curie grant agreement No. 897098 (AIE-RTP-PLED). T.W. acknowledges support from the Marie Skłodowska-Curie Individual Fellowship. The auhors thank the EPSRC (EP/R035164/1) for financial support.Collections
Items in the St Andrews Research Repository are protected by copyright, with all rights reserved, unless otherwise indicated.