Long-Range Order in Solutions and Films of Poly(3-hexylthiophene): Role of Self-Assembly and Capillary Flow in Processing

Poly(3-hexylthiophene) (P3HT) has been studied as a model conjugated polymer to understand how processing of solutions can impact film morphology and charge carrier mobility for potentially inexpensive, large area, flexible and lightweight organic electronic devices such as organic light-emitting diodes (OLED), Organic Photovoltaics (OPV) and Organic Field-Effect Transistors (OFET). In this study, we find that self-assembly that occurs with aging time in P3HT solutions can facilitate the formation of ordered, birefringent fluids through capillary flow.  Drawing these liquid crystalline fluids into thin films shows that order achieved in the solution can be maintained after solvent evaporation.  Semiconducting organic materials with long range order and few grain boundaries are highly desirable for achieving fast charge transport over macroscopic length scales. Polarized optical microscopy (POM), UV-Vis Spectroscopy, Raman spectroscopy and dynamic light scattering are used to probe solution-state ordering while POM, atomic force microscopy, and OFET device fabrication and testing are used to probe the solid state ordering and the resulting charge carrier mobility.