Center for Functional Nanomaterials Seminar

Organic semiconductors have been studied extensively in recent decades due to their potential to reduce both the material and production costs of electronic devices. Materials developed for applications such as organic photovoltaics (OPVs), organic light emitting diodes (OLEDs), and organic field effect transistors (OFETs) often have similar chemical structures and functionality, and thus can be expected to share similar structure-property relationships. In this talk, I highlight a series of studies where I use and develop synchrotron X-ray techniques to elucidate the morphology of organic semiconducting materials in order to advance our understanding of how nanostructure impacts performance. In the first half of my talk, I will show how wide angle X-ray scattering (WAXS) can be used to monitor the crystal structure of poly(3-hexylthiophene) (P3HT), in situ, during electrochemical doping. By simultaneously probing crystal structure and electrochemical performance, a clear picture of the electrochemical doping process in P3HT emerges. The results found for this model P3HT system have been shown to be consistent with several other studies of OFET devices, demonstrating the generalized nature of the doping process. The second half of my talk is focused on developing resonant soft X-ray reflectivity (RSoXR) as technique to probe the through-film structure of organic thin films. I begin by demonstrating how resonant-enhanced X-ray contrast can be utilized to detect phase segregation in thin films of small-molecule/polymer semiconductor blends, which enables their remarkable performance in OFET devices. Next, I discuss how polarized soft X-rays can enable the study of molecular orientation in thin films. Finally, using a small-molecule model system, I demonstrate how polarized-RSoXR can be used to depth-profile molecular orientation, even in amorphous single-component films. Although these studies are focused on organic electronic