Enhancing Molecular Alignment and Charge Transport of Solution-Sheared Semiconducting Polymer Films by the Electrical-Blade Effect

Controlling polymer chain alignment through processing is a means of tuning the charge transport of solution-based conjugated polymers. In this work, a processing strategy is proposed in which an external electric field (E-field) is applied to the coating blade (E-blade) to align polymer chain during solution-shearing, a meniscus-guided coating technique. A theoretical model based on dielectrophoresis quantitatively describes and predicts the alignment process and is used to guide the selection of the optimal conditions of the applied E-field. Using these conditions, more than twofold increase in chain alignment is observed for E-bladed thin films of a diketopyrrolopyrrole (DPP) semiconducting polymer without affecting other morphological aspects such as film thickness, film coverage, or fiber-like aggregation. Organic field effect transistors based on the E-bladed DPP polymer are fabricated at ambient conditions and over areas of a few cm(2). They display a threefold improvement in their mobilities and a strong enhancement in charge transport anisotropy compared to films prepared without E-field. These results reveal a synergistic alignment effect from both the solution-shearing process and the applied E-field, and introduce a novel and general approach to control the morphology and the electrical properties of solution-coated conjugated polymer thin films.