Over the last three decades, organic semiconductors, both polymeric and
small-molecule compounds, have raised significant interest in academia and industry
in view of the attractive combination of their versatile optoelectronic properties,
lightness, flexibility and potential for low-cost and straight-forward manufacturing
that makes them a valid alternative to conventional inorganic semiconductors.
Thereby, 6,13-bis(triisopropylsilylethynyl) (TIPS) pentacene and other pentacene and
anthradithiophene derivatives are interesting candidate materials for electronic
applications such as organic field-effect transistors (OFETs) as they feature highly
promising device performance and offer the possibility of processing them from
solution, originating from their good solubility in common solvents. However, the
small-molecule nature of these compounds often renders the control of the solid-state
morphology of architectures deposited from solution challenging, thus, resulting in
low reproducibility of their transistor characteristics.
This thesis explores possible pathways to control the thin-film microstructure
of such small molecules. By doing so, we aim to provide model systems that permit
the elucidation of relevant electronic processes in these materials and to provide
architectures for future technological exploitation. A thorough analysis is presented
including the influence of the selection of solvent, casting temperature, coating
techniques and the presence of small-molecular additives on the morphology of such
semiconducting small-molecule thin films. Various strategies for chemical
modification of TIPS pentacene are also discussed with focus of the effect of sidechain
substitution on the electronic properties of the resulting architectures. Furthermore, investigations into the supramolecular arrangements that can be realised
with some of those low-molecular-weight materials are presented and how this affects
their optoelectronic features.