Probing polaron-induced exciton quenching in TADF based organic light-emitting diodes

Monirul Hasan; Siddhartha Saggar; Atul Shukla; Fatima Bencheikh; Jan Sobus; Sarah K M McGregor; Chihaya Adachi; Shih-Chun Lo; Ebinazar B Namdas

doi:10.1038/s41467-021-27739-x

Probing polaron-induced exciton quenching in TADF based organic light-emitting diodes

Nat Commun. 2022 Jan 11;13(1):254. doi: 10.1038/s41467-021-27739-x.

Authors

Monirul Hasan^{1

2}, Siddhartha Saggar^{1

2}, Atul Shukla^{1

2}, Fatima Bencheikh³, Jan Sobus^{1

2}, Sarah K M McGregor^{2

4}, Chihaya Adachi⁵, Shih-Chun Lo^{6

7}, Ebinazar B Namdas^{8

9}

Affiliations

¹ School of Mathematics and Physics, The University of Queensland, Brisbane, QLD, 4072, Australia.
² Centre for Organic Photonics & Electronics, The University of Queensland, Brisbane, QLD, 4072, Australia.
³ Center for Organic Photonics and Electronics Research, Kyushu University, Fukuoka, 819-0395, Japan.
⁴ School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, QLD, 4072, Australia.
⁵ Center for Organic Photonics and Electronics Research, Kyushu University, Fukuoka, 819-0395, Japan. adachi@cstf.kyushu-u.ac.jp.
⁶ Centre for Organic Photonics & Electronics, The University of Queensland, Brisbane, QLD, 4072, Australia. s.lo@uq.edu.au.
⁷ School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, QLD, 4072, Australia. s.lo@uq.edu.au.
⁸ School of Mathematics and Physics, The University of Queensland, Brisbane, QLD, 4072, Australia. e.namdas@uq.edu.au.
⁹ Centre for Organic Photonics & Electronics, The University of Queensland, Brisbane, QLD, 4072, Australia. e.namdas@uq.edu.au.

Abstract

Polaron-induced exciton quenching in thermally activated delayed fluorescence (TADF)-based organic light-emitting diodes (OLEDs) can lead to external quantum efficiency (EQE) roll-off and device degradation. In this study, singlet-polaron annihilation (SPA) and triplet-polaron annihilation (TPA) were investigated under steady-state conditions and their relative contributions to EQE roll-off were quantified, using experimentally obtained parameters. It is observed that both TPA and SPA can lead to efficiency roll-off in 2,4,5,6-tetra(9H-carbazol-9-yl)isophthalonitrile (4CzIPN) doped OLEDs. Charge imbalance and singlet-triplet annihilation (STA) were found to be the main contributing factors, whereas the device degradation process is mainly dominated by TPA. It is also shown that the impact of electric field-induced exciton dissociation is negligible under the DC operation regime (electric field < 0.5 MV cm^-1). Through theoretical simulation, it is demonstrated that improvement to the charge recombination rate may reduce the effect of polaron-induced quenching, and thus significantly decrease the EQE roll-off.