We developed a facile post-deposition method for preparing high-performance organic transistors using direct solvent exposure. The morphological, optical, and electrical properties of poly(3-hexylthiophene) (P3HT) films were profoundly influenced by the solubility of P3HT in a solvent. Exposure to an optimized binary solvent mixture comprising methylene chloride and toluene efficiently improved the morphology and molecular ordering in a conjugated polymer thin film. The improved ordering was correlated with improved charge carrier transport in the field-effect transistors (FETs) prepared from the films. The correlation between the thin films' structural features and the electrical properties of the films guided the identification of an appropriate binary solvent mixing ratio and characterized the influence of the physical properties on the electronic properties of solvent-exposed P3HT films in an FET.