Effects of order and disorder on field-effect mobilities measured in conjugated polymer thin-film transistors

The morphol. of conjugated polymer thin films was controlled by exploiting the processes giving rise to solvatochromism in the initial polymer solns. from which the polymer films were deposited by spin coating. The material used was poly[3-[2-((S)-2-methylbutoxy)ethyl]thiophene] (I). Starting with I dissolved in good solvent (THF), various quantities of bad solvent (MeOH) when added led to the reorganization of the solubilizing side chains attached to the conjugated polymer backbone. Ordering of these side chains increased with addn. of bad solvent decreasing the flexibility of the backbone, yielding more rigid rodlike polymer chains. This in turn caused aggregation and finally pptn. This mol. order could be transferred from soln. to solid film during the spinning process, ascertained from optical spectroscopy. With these films acting as the active layer in a field-effect transistor structure, the mobility of the carrier injected into the films could be measured. As the mol. order and aggregation increased, carrier mobility decreased from .apprx.10-5 cm2 V-1 s-1 to ?10-8 cm2 V-1 s-1 in films displaying the highest degree of mol. order. This was ascribed to the increased interchain sepn. in the ordered systems along with effects due to macroscopic aggregate grain boundaries. [on SciFinder (R)]