Effect of Alcohol Polarity on the Aggregation and Film-Forming Behaviors of Poly(3-hexylthiophene)

Solvent-Additive engineering has been demonstrated to be an effective strategy for preparing highly crystalline organic semiconductors. Here, we investigate how the physicochemical properties of a solvent additive influence not only the aggregation of a polymer but also its film-forming behavior. We chose alcohol-based polar solvents as poor solvent additives that induce polymer aggregation when added to a polymer solution. We subsequently demonstrated that the polarity of the solvent additive strongly affects its miscibility with the main solvent and the ability of the resultant mixed solvent to dissolve the conjugated polymer poly(3-hexylthiophene) (P3HT); this solvation ability was related to the intermolecular force of the dipole-dipole interaction. On the contrary, we found that during polymer film formation by spin-coating, the evaporation sequence and solvent composition play more influential roles than dipole-dipole interactions in determining the crystallinity of the resultant polymer film. On the basis of the understanding of polymer aggregation gained in this work, we attained a highly crystalline P3HT film with enhanced field-effect mobility. The approach presented in this study provides a range of opportunities for the solution processing of organic electronics for various applications.