Universität zu Köln

Herzhoff, Robert ORCID: 0000-0001-8844-9256 (2026). Multiscale modeling of charge transport and excited-state properties in organic functional materials. PhD thesis, Universität zu Köln.

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Abstract

This thesis is based on the multiscale modeling of organic functional materials for Organic Electronic applications, considering both charge transfer as well as photophysical properties and processes. Additionally, related work concerning method development for the evaluation of charge transport parameters is reported. The first part of the thesis focuses on structure-property relationships with regard to the hole (hopping) transport in triphenylamine derivatives, considering the limit cases of crystalline and amorphous bulk structures. Excellent agreement of the simulated hole mobilities with the available experimental data was achieved, validating the modeling approach. A complex interdependency of molecular and bulk structure was found, where the molecular structure is reflected in the bulk morphology, influencing charge transport parameters and -anisotropy as well as hole mobility. The energetic disorder resulting from the inclusion of electrostatic effects on the site energies reflects the degree of morphological order, showing discrete distributions in the crystalline case and Gaussian-like distributions in the amorphous case. The same pattern was found for the electronic couplings. In the second part of the thesis, the electronic and ionic transport in oxetane-functionalized and polymerized triphenylamine derivatives for electrochemical applications was investigated. As main findings, it could be shown that a) charge transport is possible in the presence of high static energetic disorder due to simultaneously high dynamic disorder, and b) that this charge transport can not be described by the standard approach of kinetic Monte Carlo using a fixed set of rates. Therefore, a new descriptor for the charge transport, the effective Marcus residence time, which encompasses the dynamic disorder, was devised. Furthermore, slow ion transport was found compared to the timescales of hole transport, indicating the ion diffusion as the rate limiting step in electrochemical applications. The generally slow ion diffusion can be related to the low average void radii found in the bulk morphologies. In the third part, an implementation of a charge- and spin-constraining methodology in the framework of the density functional extended tight-binding based method called GFN2-xTB is reported and tested, aiming at the rapid evaluation of energy, gradients (i.e. geometry optimizations) and generally charge transport parameters, requiring charge or spin constraints. Finally, the excited state characterization of novel emitter compounds at a DFT based quantum chemical level is reported. Unraveling the relationship of molecular design and photophysical properties, the influence of a spiro[acridine-9,9’-fluorene] group as donor unit was found to increase the reverse intersystem crossing rate by lowering the adiabatic singlet triplet gap and the excited state reorganization energy.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Herzhoff, Robert robertherzhoff@web.de https://orcid.org/0000-0001-8844-9256 UNSPECIFIED
URN:	urn:nbn:de:hbz:38-803418
Date:	2026
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Faculty of Mathematics and Natural Sciences > Department of Chemistry > Institute of Physical Chemistry
Subjects:	Chemistry and allied sciences
Uncontrolled Keywords:	Keywords Language charge transport, ion transport, OMIEC, organic mixed electronic-ionic conductors, organic semiconductors, triphenylamine, hopping transport, organic electronics, computational chemistry, hole transport material, organic batteries, polymer batteries, molecular dynamics, kinetic monte carlo, TADF, OLED English
Date of oral exam:	23 January 2026
Referee:	Name Academic Title Meerholz, Klaus Professor Wenzel, Wolfgang Professor Blumberger, Jochen Professor
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/80341