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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 32: Focus: Triplet States in Organic Optoelectronics I

CPP 32.4: Vortrag

Mittwoch, 9. März 2016, 10:30–10:45, H37

Understanding and predicting the orientation of heteroleptic phosphors in organic light-emitting diodes — •Tobias D. Schmidt¹, Matthew J. Jurow², Christian Mayr¹, Thomas Lampe¹, Peter I. Djurovich², Mark E. Thompson², and Wolfgang Brütting¹ — ¹Institute of Physics, University of Augsburg, 86135 Augsburg, Germany — ²Department of Chemistry, University of Southern California, 90089 Los Angeles, USA

Horizontal orientation of dye molecules, i.e. their transition dipole vectors (TDV), is a powerful feature improving the efficiency of organic light-emitting diodes. In order to understand the underlying mechanisms for emitter orientation of heteroleptic phosphors, we compared the anisotropy factor of emissive guest/host systems using different Ir-complexes incorporating coumarin and phenylpyridin based ligands. These molecules exhibit similar high permanent dipole moments and electrostatic surface potentials but differ in the molecular structure. Interestingly, only molecules with aromatic and aliphatic ligands show non-isotropic distributions of their TDVs when co-deposited with a matrix material by thermal evaporation. From these findings we conclude that molecular orientation of heteroleptic Ir-complexes occurs instantaneously at the surface of the growing film and is driven by chemical interactions with the surrounding media. Furthermore, it was possible to predict the anisotropy factor for arbitrary molecular orientation with a mathematical model taking into account the geometrical distribution of the TDV on the molecules.¹
[1] M. Jurow et al., Nature Materials (2015), doi:10.1038/nmat4428