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Institut für Festkörperphysik
Charge mobility in organic semiconductors and covalent organic frameworks using the newly developed transient localization theory
Despite the fact that organic semiconductors (OSCs) have been known and extensively investigated for several decades, the mechanism of charge transport in these materials is still hotly debated. Nevertheless, it is increasingly accepted that the charge carrier dynamics in organic semiconductors is strongly determined by a coupling to low frequency inter-molecular phonons. Due to the similar energy scales of the phononic relaxation of charge carriers and the inter-molecular electronic coupling strengths, the charge carrier dynamics in OSCs is hard to model properly. Recently, a new approach – the transient localization model - has been introduced and successfully applied to various important OSCs. An advantage of this approach is that by avoiding an explicit consideration of quantum dynamics, it becomes tractable also for rather complex systems. The goal of this Master thesis is to first implement this model and to benchmark it against reported results for organic semiconductors. Subsequently, it shall for the first time be applied to covalent organic frameworks, a highly promising class or materials that is related to organic semiconductors, but consists of a fully covalently linked, porous network. From these studies unprecedented insight into the charge carrier dynamics in these advanced materials can be expected. Notably, the input parameters needed for the transient localization model (the electronic structure of the OSCs and COFs as well as the properties of phonons in these materials) are commonly calculated in our group and can be provided by other group members.
Understanding the physical origins of the electrical conductivity in Covalent Organic Frameworks
2 MASTER THESES
Conductive organic materials have interesting electronic and optoelectronic properties, high mechanical flexibility and can be designed/functionalized quite easily. Thus, they are highly relevant for a huge variety of applications such as transistors, optoelectronic devices, and solar cells. Efficient charge-carrier transport is essential in all these applications.
Search for new polymorphs by organic epitaxy
The aim of the study is to study the crystallographic property of molecular crystals at single crystalline surfaces. Organic semiconducting molecules will be crystallized at surfaces and the crystallographic properties will be investigated by grazing incidence X-ray diffraction. The position of Bragg peaks will be used for indexing to identify the crystallographic phase. The final goal of the study is to solve the crystal structure of epitaxially grown crystallites.A part of the experiments will be performed at beamline XRD1, synchrotron Elettra, Trieste.
Autonomous Driving for Nanocars
Machine Learning, Exp.-Theory Collaboration, STM, Surface Science
The advent of Machine Learning methods has unlocked great potential in computational studies. In particular the exploration of surface structures, that was previously thought to be completely unfeasible, has surged in the recent years. At the same time, machine learning studies are often criticized for their lack of physical insight.
Goal: Development of atomistically motivated structure-to-property relationships for heat transport in organic semiconductors – a property, that is crucial for device operation, but is still largely unexplored such that the suggested studies can have a huge impact.
The molecule HATCN is a strong electron acceptor that is commercially used in OLEDs to modify the property of metal substrates. Adsorbed on silver, this molecule shows unusual, fascinating physics. At low coverage, the molecule forms honeycomb patterns, which can be exploited as epitaxial growth template. When the coverage is increased, however, the first monolayer rearranges. This drastically changes the material properties, in particular the system’s work function.