Berlin 2018 – wissenschaftliches Programm
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HL: Fachverband Halbleiterphysik
HL 54: Organic semiconductors
HL 54.1: Vortrag
Freitag, 16. März 2018, 09:30–09:45, EW 203
Molecular origin of the anisotropic orientation of molecules in organic light emitting diodes — •Pascal Friederich1, Vadim Rodin2, Florian von Wrochem2, Reinder Coehoorn3, and Wolfgang Wenzel1 — 1Karlsruher Institut für Technologie, Karlsruhe, Deutschland — 2Sony, Stuttgart, Deutschland — 3Technische Universität Eindhoven, Eindhoven, Niederlande
Molecular orientation anisotropy of the emitter molecules used in organic light emitting diodes (OLEDs) can give rise to an enhanced light-outcoupling efficiency, when their transition dipole moments are oriented preferentially parallel to the substrate. A similar effect is observed when the anisotropic orientation of molecules with electrostatic dipole moments leads to the spontaneous buildup of an electrostatic potential perpendicular to the substrate. This so-called giant surface potential (GSP) effect can as well be exploited in organic electronics applications. Here, the orientation anisotropy of widely used organic semiconductors is investigated using a simulation approach which mimics the physical vapor deposition process of amorphous thin films [1]. Our simulations reveal for all studied systems significant orientation anisotropy which is in agreement with experimental results for the emitter orientation as well as the GSP effect. We find that the electrostatic interaction between the dipole moments of the molecules limits the orientation strength while short range van der Waals interactions between molecules and the surface during deposition act as driving force for the anisotropic orientation. [1] P. Friederich, R. Coehoorn, W. Wenzel, Chem. Mater., 2017, 29 (21)