Electron and Spin Transport in Soft Matter: From Fundamentals to Applications

• Applicant: Professor Dr. Frank Ortmann
• Subject Area: Theoretical Condensed Matter Physics
• Term: from 2014 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 243752782

The project aims at advancing the field of electronic transport and spin transport in organic semiconductors. We aim at contributions that will encompass very fundamental insight in basic mechanisms of interacting electrons and phonons in disordered systems, charge transport and spin transport for application-relevant materials including the ab initio description of basic material properties. One corner stone of the project is the simulation of transport processes in organic semiconductors that are doped to gain functionality in actual devices such as organic light emitting diodes or organic solar cells. By employing highly efficient simulation tools, we will simulate the influence of doping molecules at a microscopic level and their impact on the macroscopic charge carrier transport in the organic host material. Based on this we will provide guidelines for improved performance.This will be achieved by employing ab initio material parameters that enter the multiscale ansatz for charge transport. The link between transport modelling and microscopic ab initio material parameters will provide novel insights, cast new light on physical effects and will provide valuable feedback to experimentalists.In the first phase of the Emmy Noether project, we studied such microscopic energetic properties of doped systems with ab initio methods. We developed models which describe with high accuracy the energetics of doped films. These models will be further refined and enhanced towards application in transport simulations.Spin dependent transport phenomena are another subject of the project, which are researched in organic semiconductor devices. We succeeded in describing both organic transistors with non-equilibrium (hot) electrons and investigated the spin currents. We have also predicted the occurrence of pure spin currents in such devices.Finally, another research line within the project addresses fundamental aspects related to the charge carriers, electrons and holes, in organic semiconductors. Localization aspects have been studied in terms of the polaron relaxation. This phenomenon describes the geometrical distortion of the molecular structure upon charging (trapping). Here, we have introduced the concept of the reduced relaxation energy, which describes the influence of molecular vibrations on the electronic properties. The importance of this concept for charge transport is yet unclear and will be investigated in the course of the continued project. Another focus will be on Hall transport simulations for which we have done substantial preliminary work, rounding off the project in its activity.

• DFG Programme: Independent Junior Research Groups