Dresden 2014 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 23: Organic Electronics and Photovoltaics III (DS jointly with CPP, HL, O)
O 23.6: Vortrag
Montag, 31. März 2014, 19:15–19:30, CHE 91
Efficiency roll-off in organic light-emitting diodes: influence of emitter position and orientation — •Caroline Murawski1, Philipp Liehm1,2, Simone Hofmann1, Karl Leo1, and Malte C. Gather1,2 — 1Institut für Angewandte Photophysik, Technische Universität Dresden, 01062 Dresden, Germany — 2present address: SUPA, School of Physics and Astronomy, University of St Andrews, St Andrews KY16 9SS (UK)
In this contribution, we study the efficiency decrease of organic light-emitting diodes (OLEDs) at high brightness (so-called roll-off).[1] We find a strong influence of the emitter-cathode distance and the transition dipole orientation of the emitter molecules on the roll-off by comparing two phosphorescent emitters (Ir(MDQ)2(acac) and Ir(ppy)3).[2] The measurements are modeled using triplet-triplet-annihilation (TTA) theory. A comparison of experiment and theory reveals the critical current density and the TTA rate constant and shows that the differences in roll-off behavior are predominantly caused by a change of the decay rates inside the OLED cavity. In order to provide guidelines for designing OLEDs with optimal high-brightness efficiency, we model the roll-off as a function of the emitter-cathode distance, emitter dipole orientation, and radiative efficiency.
[1] C. Murawski, K. Leo, and M.C. Gather, Adv. Mater. 10.1002/adma.201301603 (2013).
[2] C. Murawski, P. Liehm, K. Leo, and M.C. Gather, Adv. Funct. Mater. 10.1002/adfm.201302173 (2013).