Dresden 2017 – wissenschaftliches Programm
DS 34.2: 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 80∘C which is only 5% below the glass transition temperature of NPB.