Dresden 2014 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 54: Organic Electronics and Photovoltaics V (CPP jointly with DS, HL, O)

O 54.1: Vortrag

Mittwoch, 2. April 2014, 15:00–15:15, ZEU 260

Comprehensive efficiency analysis of organic light-emitting diodes featuring horizontal emitter orientation and triplet-to-singlet up-conversion — •Tobias Schmidt¹, Bert Scholz¹, Christian Mayr¹, Andreas Rausch², Thomas Wehlus², Dirk Michaelis³, Norbert Danz³, Thilo Reusch², and Wolfgang Brütting¹ — ¹Institute of Physics, University of Augsburg, 86135 Augsburg, Germany — ²OSRAM Opto Semiconductors GmbH, Leibnizstrasse 4, 93055 Regensburg, Germany — ³Fraunhofer Institute for Applied Optics and Precision Engineering, 07745 Jena, Germany

The external quantum efficiency (EQE) of an organic light-emitting diode can strongly be affected by orientation of the emissive dipole moments, and for fluorescent dyes, by triplet-to-singlet up-conversion leading to an enhanced radiative exciton fraction (η_r), exceeding the spin-statistical limit of 25 %. By a combination of EQE investigations with time resolved photo- and electroluminescence measurements we are able to quantify the lower limit of the additionally created singlet excitons, e.g. by thermally activated delayed fluorescence, as well as the factors being responsible for light-outcoupling. For the investigated fluorescent system the EQE is boosted by two effects. First, due to horizontal alignment of the transition dipole moments, the outcoupling factor is enhanced by a factor of 1.3. Second, the enhanced η_r value of 36 %, results in an additional efficiency increase by a factor of 1.44. As a consequence of the combination of both effects the EQE almost doubles and values up to 5 % are achieved for direct emission in spite of a comparatively low emitter efficiency of 40 % only.