Structural Order, Crystallinity, and Processing Effects in Organic Semiconducting Systems

Organic photovoltaic devices have attracted significant interest as lightweight, flexible, and solution-processable renewable-energy technologies. Their performance is strongly influenced by the morphological organization of the active layer, which affects charge photogeneration, transport, recombination, and collection processes. Understanding how specific structural and processing-related characteristics influence device behavior therefore remains an important topic within organic electronics.

This thesis investigates the influence of highly ordered interfaces, crystallinity, and processinginduced morphological modifications on the optoelectronic behavior of organic semiconducting systems through the study of deliberately simplified and well-defined model structures. In this context, three complementary research topics were investigated. The first research topic investigated the influence of crystal-crystal interface formation in highly ordered rubrene-based systems, revealing enhanced conductivity and charge transport associated with crystalline interfacial effects.

The second study explored the incorporation of a rubrene single-crystal donor within planar heterojunction organic solar cells, demonstrating efficient photovoltaic generation at crystalline donor/acceptor interfaces and providing insight into the role of highly ordered donor phases. Finally, the third research topic evaluated the replacement of conventional halogenated solvents by green-solvent alternatives in Y12-based planar heterojunction solar cells, showing that green-solvent processing modifies active-layer nanoscale organization while producing comparable or enhanced photocurrent generation.

By investigating simplified model systems exhibiting distinct forms of structural order and processing-induced morphological variation, this work contributed to the understanding of morphology-related effects in organic semiconducting heterojunctions and provided additional insight into the relationship between structural organization and optoelectronic behavior in organic semiconducting systems