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

• Published in: Nature communications Vol. 13; no. 1; p. 254
• Main Authors: Hasan, Monirul, Saggar, Siddhartha, Shukla, Atul, Bencheikh, Fatima, Sobus, Jan, McGregor, Sarah K. M., Adachi, Chihaya, Lo, Shih-Chun, Namdas, Ebinazar B.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 11.01.2022; Nature Publishing Group; Nature Portfolio
• Subjects: 639/301/1019; 639/624/1020/1091; Degradation; Efficiency; Electric fields; Excitons; Fluorescence; Humanities and Social Sciences; Light emitting diodes; multidisciplinary; Organic light emitting diodes; Polarons; Power consumption; Quantum efficiency; Quenching; Recombination; Science; Science (multidisciplinary)
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-021-27739-x

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(9 H -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. Efficiency roll-off in organic light-emitting diodes under elevated current densities not only results in high power consumption but also device degradation. Here, the impact of polaroninduced quenching in efficiency roll-off was investigated and strategies to reduce efficiency roll-off were proposed.