Effect of Solvent Exchange at the Biphasic Dip-Coating Interface on the Formation of Polythiophene Thin Films

The biphasic dip-coating method reduces the amount of solution required for coating by using a phase-separated biphasic solvent system and is highly promising for the preparation of large-area thin films with applications in electronic devices. We studied the effects of varying the miscibility of the low-lying secondary solvent and the high-lying polymer-dissolving solvent on polymer crystallization and on the resulting films. We systematically chose three kinds of solvents with high density for use as the low-lying solvent phase and compared the miscibilities of the low-lying solvents and the high-lying polymer solution in terms of their Hansen solubility parameters (HSPs). We demonstrated that the HSP distance is correlated with the degree of intermixing of the low-lying and high-lying solvents and determined the effects of intermixing on polymer aggregation and stability in the solution state for various aging times. The degree of solvent exchange at the interface also determines the film morphology and charge carrier mobility of the resulting dip-coated P3HT thin film. This study confirms the potential of biphasic dip-coating as a scalable film preparation method for use in large-area flexible electronics.