Conjugated polymers have attracted significant interest for organic electronics such as polymer photovoltaics and transistors, due to their potential low cost, light-weight and flexible nature. The charge carrier mobility of these devices can be enhanced with long range macromolecular ordering. Poly(3-hexylthiophene) (P3HT) has recently been shown to exhibit lyotropic liquid crystalline properties after the formation of self-assembled nanowires in solution which can yield long-range alignment. We have shown that the self-assembly and the resulting transition from isotropic to birefringent solutions is time-dependent, requiring a certain percentage of polymer to aggregate (as determined by UV-Vis analysis). Furthermore, we show that not only is the percent of aggregates important, but the length of the nanowires, as controlled by various aggregation techniques is critical to the emergence of a birefringent fluid. P3HT solutions that are sonicated to induce aggregation result in significantly shorter fibers than with aging (as determined by AFM of spincast films), and as a result, yield isotropic solutions. The relationship between solution-state ordering and the resulting thin film morphological and electrical properties was also explored, through GIWAXS, optical microscopy, AFM, UV-Vis, Raman, and Organic Field-Effect Transistor fabrication and testing. Through various combinations of sonication and aging, high mobility organic field effect transistors were fabricated with an order of magnitude increase in charge-carrier mobility vs. the pristine P3HT solution. These explorations into the evolution of solution-state ordering and the relationship between ordered fluids and resulting ordered thin-films gives further insight into the control of semiconducting polymer ordering for high performance organic electronics applications.

Long range ordering of poly(3-hexylthiophene) in fluids and films: Effects of self-assembly techniques on liquid crystallinity, material properties and device performance

251st National Meeting (2016)

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