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Dresden 2011 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 8: Poster: Organic Semiconductors

CPP 8.37: Poster

Monday, March 14, 2011, 17:30–19:30, P2

Determination of molecular dipole orientation in organic films — •Christian Mayr, Jörg Frischeisen, and Wolfgang Brütting — University of Augsburg, Institute of Physics, Germany

Organic light-emitting diodes (OLEDs) have been investigated for 20 years standing now at the frontier to mass production. Current research focuses on the enhancement of light outcoupling efficiency which is reduced especially by the excitation of surface plasmons (SPs) at the interface to the cathode. The orientation of molecules in films used in OLEDs has a huge effect on the coupling to SPs. Numerical simulations show that a horizontal molecular orientation with respect to the substrate can enhance the efficiency by up to 50%.
An expeditious method to determine the orientation of the transition dipole moment of molecules has been developed using angular dependent photoluminescence spectroscopy. By comparing measurement with simulations, the orientation can be quantitatively determined. Although other methods to measure molecular orientation exist, the presented method makes it not only possible to study molecular orientation in neat thin films but also of small amounts of emitters doped into a matrix material without knowing any information of the optical properties of the dopant. Hence, this method is particularly useful for the investigation of newly developed materials. Measurements of the phosphorescent emitter Ir(ppy)3 doped into a CBP-matrix and of other neat and doped organic materials have been performed. With this method a deeper understanding of OLEDs and possibilities to enhance light outcoupling can be gained.

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