Title: The Effect of (Counter-)ions on the Electronic and Crystalline Structure of Doped Polymeric Semiconductors
Polymeric semiconductors show potential as materials for electronics unrealizable by inorganic semiconductors, such as wearable and biocompatible devices. An important process to increase the electrical conductivity in polymers is through doping, where small molecules infiltrate the material to oxidize or reduce the polymeric backbone. Once the reaction takes place, the dopant molecule becomes ionized. A central concept that is not understood in polymeric semiconductors today is how these counter-ions and electrons (or holes) interact when in close proximity to one another, and how those interactions affect their respective conduction mechanisms. Additionally, the semi-crystalline nature of most semiconducting polymers complicates the relationship between morphology and charge transport.
This dissertation aims to develop a better understanding of ionic effects on the electronic and morphological properties of semiconducting polymers using a combination of spectroscopic measurements, X-ray scattering, and electrical characterization. The results discussed herein demonstrate that the presence of dopant counter-ions manifests through a continuum of length scales that partially govern the electronic behavior at the device scale. This work indicates that significant differences exist between a doped polymer and its insulating state, signifying the importance of integrating doping-induced disorder into transport models for organic semiconductors.