Controlling Spontaneous Orientation Polarization in Organic Semiconductor Mixtures and its Impact on Excitons in Optoelectronic Devices

• Applicant: Professor Dr. Wolfgang Brütting
• Subject Area: Experimental Condensed Matter Physics
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 565002384

Spontaneous orientation polarization (SOP) occurs when molecules with a finite permanent dipole moment are grown into a thin film by physical vapor deposition and their alignment is such that a net non- zero polarization remains. It manifests itself by a so-called giant surface potential -- typically of the order of some 10 - 100 mV/nm (or equivalently 10 - 100 MV/m of electric field strength) -- or the presence of surface/interface charges of a few mC/m². Most of the research on SOP so far has focused on single-component neat films of polar organic molecules, although dilution of a polar species in a non-polar matrix, i.e. dipolar doping, has been studied in some cases. Here, we focus on binary mixtures of SOP materials with another (non)polar species, as well as on the behavior of excitons in such systems where either the mixture itself forms an intermolecular excited state, i.e. a so-called exciplex that emits light, or a third emissive species is doped into an SOP (co)host matrix. The main goals of this project are, on the one hand, to attain further insights into the driving forces for SOP in organic semiconductor mixtures and find design rules for controlling it. On the other hand, we will investigate the impact of SOP on excitons in light-emitting systems that are relevant for device applications.

• DFG Programme: Research Grants
• International Connection: Japan
• Co-Investigators: Dr. Alexander Hofmann; Professor Dr. Frank Schreiber
• Cooperation Partner: Professor Dr. Yutaka Noguchi