Crystallinity and performance improvement in solution processed organic field-effect transistors due to structural dissimilarity of the additive solvent

The effect of structural dissimilarity of the additive solvent from the main solvent on the properties of the solution and resulting crystals for solution processed organic field-effect transistors (OFETs) is comprehensively studied. Organic semiconductor TIPS-Pentacene was explored with toluene as the main solvent and benzene, cyclohexane, and hexane as additives for making semiconductor solutions. The solution formation with various solvents is explained by Hansen's solubility theory, according to which the binary solvent with higher structural dissimilarity between constituent solvents is a weaker solvent of the organic semiconductor; which eventually supports better molecular aggregation and crystallinity in the resulting crystallites. As investigated by XRD, the degree of crystalline order systematically increased with rising dissimilarity in component solvents; integrated intensity ratio rising from 0.52 for toluene to 0.54, 0.69 and 0.72 respectively for toluene/benzene, toluene/cyclohexane, and toluene/hexane. The variation in degree of crystallinity is also reflected in electrical properties of OFETs, where the field-effect mobility improved from 0.05 cm2/(V.s) for toluene solvent to higher than 0.1 cm2/(V.s) for toluene/hexane.