An Oligomer Approach for Advancing the Field of Organic Electronics
The rapid development of synthetic conjugated materials has enabled organic electronic devices such as solar cells, field-effect transistors and sensors to rival their inorganic counterparts in performance at significantly lower cost. Conducting polymers such as polyaniline constitute an important class of such materials, but their properties are difficult to study due to polydispersity, complex chain conformations and lack of solubility. In particular, assembling conducting polymers into highly crystalline domains similar to that of small molecule (semi)conductors has proven to be challenging, which has limited their integration into electronic devices that require high carrier mobility and stability such as organic field-effect transistors and solar cells. On the other hand, oligomers represent a unique middle ground between conducting polymers and molecular (semi)conductors because oligomers (e.g. oligoanilines) retain the chemical properties of the parent polymer, while also possessing properties typically associated with molecular (semi)conductors especially in regard to monodispersity and self-assembly. In this thesis, an oligomer approach for advancing the field of conducting polymers is presented. A myriad of conjugated oligomers are examined as the more structurally rigid, pure, and soluble model systems to tackle important challenges in this field. This approach has opened new opportunities for (1) understanding the fundamental packing, transport, and self-assembly properties for polymers; (2) the rational design of high performance conducting polymers by analyzing the oligomer building blocks; (3) realizing the long-sought solution-based bottom-up growth for vertically oriented arrays of organic single crystals; and (4) deciphering the role of oligomers in improving the crystallinity of the parent polymers. The advancement of knowledge in these fields has also allowed us to create high performance hybrid solar cells, complex core/shell nanostructures, and microcontact printing methods with nanoscale resolution.