Fluctuations and exciton dynamics in molecular semiconductors
type: CreativeWork
description: This work describes experimental studies of the fluctuation-dominated electronic structure of molecular semiconductors and of the exciton dynamics in the same materials. The method employed in this thesis is time- and angle-resolved photoemission spectroscopy. In the first part, the electronic structure of molecular semiconductors at equilibrium is considered. We show that the experimental band structure of several representative molecular crystals can be described with a common tight-binding model and analyze how both the crystal structure and the π-topology impact the electronic structure. With this consistent description of the electronic states, it is discussed how fluctuations act on different materials and how they impact charge transport properties. These deliberations lead to non-trivial design rules for future materials with high charge mobilities that have been independently verified in charge transport experiments. The subsequent chapter concerns the spatial structure of the electronic states captured in momentum space. By applying the previously established tight-binding model, a strong connection between the anatomy of momentum maps, i.e., constant-energy cuts through the photoemission intensity, the electronic structure, and the real space description of electrons as Bloch states is built up. It is also discussed whether properties arising from fluctuations are visible in these maps. Most importantly, this part provides the basis for interpreting momentum maps of ground and excited states. In the second part, we analyzed the exciton dynamics in some of the same compounds that staged in the previous part. For pentacene single crystals, we obtained the first momentum maps of singlet and triplet excitons. These demonstrate the predicted, but never observed, similar orbital character and different localization properties of the two states and the images allow to study singlet exciton fission in unprecedented detail. Previous experimental results pointed to…
abstract: This work describes experimental studies of the fluctuation-dominated electronic structure of molecular semiconductors and of the exciton dynamics in the same materials. The method employed in this thesis is time- and angle-resolved photoemission spectroscopy. In the first part, the electronic structure of molecular semiconductors at equilibrium is considered. We show that the experimental band structure of several representative molecular crystals can be described with a common tight-binding model and analyze how both the crystal structure and the π-topology impact the electronic structure. With this consistent description of the electronic states, it is discussed how fluctuations act on different materials and how they impact charge transport properties. These deliberations lead to non-trivial design rules for future materials with high charge mobilities that have been independently verified in charge transport experiments. The subsequent chapter concerns the spatial structure of the electronic states captured in momentum space. By applying the previously established tight-binding model, a strong connection between the anatomy of momentum maps, i.e., constant-energy cuts through the photoemission intensity, the electronic structure, and the real space description of electrons as Bloch states is built up. It is also discussed whether properties arising from fluctuations are visible in these maps. Most importantly, this part provides the basis for interpreting momentum maps of ground and excited states. In the second part, we analyzed the exciton dynamics in some of the same compounds that staged in the previous part. For pentacene single crystals, we obtained the first momentum maps of singlet and triplet excitons. These demonstrate the predicted, but never observed, similar orbital character and different localization properties of the two states and the images allow to study singlet exciton fission in unprecedented detail. Previous experimental results pointed to…
author: Neef, Alexander
language: en
license: https://creativecommons.org/licenses/by/4.0/
date published: 2024
date modified: 2026-07-27T21:28:37Z
provider: Technische Universität Berlin
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: Technische Universität Berlin

PropertyValue
property ID: DOI
value: 10.14279/depositonce-20055