Dresden 2014 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 73: Organic electronics and photovoltaics IV (organized by CPP)

HL 73.1: 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 Brütting11Institute 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 (ηr), 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 ηr 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.

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