UC Santa Barbara

Polymeric semiconductors show potential as materials for electronic applications 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 electronic conduction.

We aim 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. From this work, we find that the presence of dopant counter-ions manifest throughout a multitude 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.