Dresden 2017 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 46: Organic Thin Films II (joint session CPP/DS/HL, organized by DS)

CPP 46.2: Vortrag

Mittwoch, 22. März 2017, 15:15–15:30, CHE 91

Determination of the molecular orientation in absorptive organic thin films — •Christian Hänisch, Simone Lenk, and Sebastian Reineke — Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP) and Institute for Applied Physics

The overall efficiency of organic light-emitting diodes (OLEDs) is mainly limited by the high refractive index of the organic layers causing a trapping of large portions of the initially emitted light. Using emitter molecules with transition dipole moments parallel to the interface planes of an OLED reduces this loss channel and hence, increases the outcoupling efficiency of the device. The orientation of the molecules’ transition dipole moments can be determined by angular resolved photoluminescence spectroscopy.

We investigate the impact of the organic layer’s absorption on the determined orientation value by evaluating the emission spectra of single organic layers with thicknesses up to 150 nm. Numerically, these emission layers are represented by a set of radiating electrical dipoles which are homogeneously distributed over the whole layer. To represent the absorption of the excitation light, the single dipoles are weighted by an exponential function according to the Beer-Lambert law.

Using this method, we can show that the orientation parameter of the red phosphorescent emitter Ir(MDQ)2(acac) doped into NPB is stable over a time range of several months at temperatures between room temperature and 80C which is only 5% below the glass transition temperature of NPB.

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