Berlin 2012 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 31: Organic semiconductors II

CPP 31.5: Talk

Thursday, March 29, 2012, 10:45–11:00, C 130

Evidence for non-isotropic emitter orientation in a red phosphorescent OLED and its implications for determining the emitter’s radiative quantum efficiency — •Tobias Daniel Schmidt¹, Michael Flämmich², Jörg Frischeisen¹, Dirk Michaelis², Norbert Danz², and Wolfgang Brütting¹ — ¹Institute of Physics, University of Augsburg, 86135 Augsburg, Germany — ²Fraunhofer Institute for Applied Optics and Precision Engineering, 07745 Jena, Germany

The efficiency of organic light-emitting diodes (OLEDs) is still limited as only a fraction of the consumed electrical power is converted into light and only a small part of this light is finally extracted from the device to air. Especially the radiative quantum efficiency (RQE) of the utilized guest-host system is of interest and should be close to unity in phosphorescent emitter/matrix combinations in order to achieve highly efficient devices. We show that the commonly used red phosphorescent emitter Ir(MDQ)₂(acac) doped in an α-NPB matrix exhibits a profound non-isotropic dipole orientation of the emitter molecules. Ignoring this feature leads to a significant overestimation of the RQE or other factors, which determine the external quantum efficiency of a device. Furthermore, we demonstrate the huge potential for efficiency enhancement of mainly parallel dipole emitter orientation in phosphorescent OLED systems.