Regensburg 2019 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 57: Organic Electronics and Photovoltaics IV - Excitonic Properties and Light-Emitting Devices

CPP 57.2: Vortrag

Donnerstag, 4. April 2019, 15:15–15:30, H18

Temperature (De-)Activation in Donor-Acceptor based Organic Light Emitting Diodes — •Sebastian Weissenseel, Felix Klingert, Jeannine Grüne, Nikolai Bunzmann, Andreas Sperlich, and Vladimir Dyakonov — Experimental Physics VI, Julius Maximilian University of Würzburg, 97074 Würzburg

The world of organic light emitting diodes (OLEDs) regained a lot of attention with the publication of Goushi et al. in 2012 [1], where the thermal activation of non-radiative triplets via reverse intersystem crossing (RISC) was applied to enhance the fluorescence in OLEDs for the first time. Here, we investigate the donor-acceptor based system 4,4’,4”-Tris(N-3-methylphenyl-N-phenyl-amino)triphenylamine (m-MTDATA): Tris(2,4,6-trimethyl-3-(pyridin-3-yl)phenyl)borane (3TPYMB), which exhibits an intermolecular TADF mechanism. The devices are analyzed by means of temperature dependent current-electroluminescence-voltage (j-EL-V) characteristics and external quantum efficiency (EQE). These measurements were intended to estimate the activation energy of the triplet-to-singlet upconversion and thus the singlet-triplet gap. Surprisingly, we observe typical TADF-like efficiency enhancement with rising temperature only in a limited temperature range 180-250K, while at higher temperature (>250K), this trend inverts and we observe a decrease in EQE. This observation implies the competing process between thermally activated RISC and a non-radiative decay at ambient temperature in TADF OLEDs, which is essential for their further improvement.
[1] Goushi, et al., Nat. Photon. 6, 253 (2012)