Dresden 2020 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 36: Focus: Exploitation of Anisotropy in Organic Semiconductors I (joint session CPP/HL)

CPP 36.4: Talk

Tuesday, March 17, 2020, 11:00–11:15, ZEU 222

Post processing temperature dependence of the emitter molecule orientation in 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, Technische Universität Dresden, Germany

One of the main loss channels reducing the efficiency of organic light-emitting diodes is optical trapping of already generated photons due to total internal reflection and coupling to plasmonic modes. Aligning the transition dipole moment of the emitter molecules parallel to the interface planes of the stratified device structure can drastically decrease the unusable power fraction.

In this work, the long term, post processing stability of the molecular orientation of two well-known phosphorescent emitters is investigated for different storage temperatures up to 95% of the glass transition temperature (Tg) of the host material. Both, photoluminescent samples and electroluminescent devices are analyzed. In the first case, the emission layers are embedded between two layers of higher Tg in order to avoid crystalization of bare emission layers.

It is shown that the orientation keeps unchanged for several months as long as Tg is not exceeded but changes immediately as soon as the samples are exposed to temperatures above Tg for only a few minutes. The latter is demonstrated exemplarily for selected samples after the long term storage period.