Regensburg 2025 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 22: Organic Electronics and Photovoltaics II

CPP 22.1: Talk

Tuesday, March 18, 2025, 14:00–14:15, H38

Spontaneous orientation polarization in mixed films of organic semiconductors — •Albin Cakaj, Alexander Hofmann, and Wolfgang Brütting — Experimental Physics IV, Institute of Physics; University of Augsburg, 86135 Augsburg, Germany

Small organic molecules processed by physical vapor deposition (PVD) can exhibit a preferential alignment, despite their tendency to form glassy amorphous films. This alignment can additionally lead to a macroscopic polarization of the film, if the molecules have a permanent dipole moment (PDM). The additional field, also referred to as giant surface potential (GSP), can impact the properties of organic light emitting diodes (OLEDs) significantly. Therefore, understanding the formation and control of this effect is of crucial importance.

We investigated different GSP forming polar molecules mixed with non-polar organic compounds. We found combinations with enhanced PDM alignment, where the impact of suppressed dipole-dipole interactions by dilution is far more significant than the effect on the film-formation process by a change in the effective glass temperature of the blend. Additionally, our data hint to the conclusion that molecules with an already high degree of PDM alignment keep their magnitude of alignment in mixed films without significant enhancement. Therefore, we can conclude that mixing of polar molecules with a non-polar compount can enhance the degree of PDM alignment significantly, if the polar molecules exhibit only a small degree of PDM alignment in the first place.

Keywords: OLED; SOP; Organics Semiconductors