Dresden 2011 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 8: Poster: Organic Semiconductors
CPP 8.37: Poster
Montag, 14. März 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.