Determinant Role of Solution‐State Supramolecular Assembly in Molecular Orientation of Conjugated Polymer Films

The solid-state molecular orientation of conjugated polymers is of vital importance for their charge transport properties, where the edge-on orientation with pi-stacking direction parallel to the surface is generally preferable to achieving high-mobility planar field-effect transistors. However, so far, little is known about the origin of packing-orientation formation in thin films. Here, it is shown that the solution-state supramolecular structure of widely studied PffBT4T-based polymers can be reversibly tuned between 1D worm-like and 2D lamellar structures for the same polymer/solvent system through solution temperature. Such dimensionality in solution determines the solid-state packing orientation of the polymer chains, where edge-on and face-on textures are generated from solutions with 1D and 2D structures, respectively. More importantly, the transition temperature of solution-state supramolecular dimensionality is in excellent agreement with that of solid-state packing orientation. These experimental observations unambiguously demonstrate the predominant roles of solution-state supramolecular assembly in solid-state molecular orientation, which is further verified using different molecular weight batches and other two representative polymers. The findings provide new insights into the growth mechanism of polymer semiconductors during transistor fabrication, and open prospective pathways for boosting device performance of solution-processable plastic electronics.