UC Berkeley

Organic semiconductors have the potential to form the basis of the next-generation of electronic devices. Device layers formed from these molecular based materials can be solution processed at room temperature using techniques such as roll-to-roll printing, making them cheaper and more sustainable than inorganic alternatives such as silicon. Furthermore, their properties also enable the development of low-weight and flexible devices to access novel applications. Yet, solution processing also leads to the formation of complex microstructure via self-assembly that strongly impacts the function of such devices. A full understanding of the dependence of device functionality on device structure is needed to direct design of organic semiconductor based devices to drive widespread commercial adoption. The work of this thesis is focused on using time-resolved spectroscopy techniques to study the structure-function relationships of various organic semiconductors as a function of their local environment.

Chapters 2-4 focus on using transient absorption microscopy to study structure-function relationships in 6,13-Bis(triisopropylsilylethynyl)pentacene, a model organic semiconductor with applications in organic field-effect transistors and organic solar cells, as a function of the local film microstructure. Chapters 5-6 then turn to a time-resolved fluorescence study of next-generation thermally-activated delayed fluorescence organic light-emitting diodes as a function of the host matrix polarity.

Organic electronics are a fascinating field of study due to the intertwined relationship between the chaotic self-assembly of the active layers of these devices and their resulting functionality. Molecular design of the building blocks of these films affects the ensemble electronic properties of the entire film not only through the molecular excited states but also by how those molecular electronic states couple together. Efforts to correlate the impact of the local physical structure of samples on the resulting local electronic structure will inform future design decisions in the organic electronics community.