Optimizing the aggregate structure and charge carrier transport performance of D-A conjugated polymer films using nonpolar solvents

Abstract

Solution-processed conjugated polymers have been widely used in the fields of electronic skin, wearable devices, and organic optoelectronic devices, due to their excellent optoelectronic properties, flexibility, and low cost. The aggregate structure of conjugated polymers determines the efficiency of charge carrier transport, thereby affecting the optoelectronic performance of the devices. In this work, we regulated the crystalline behavior and aggregated state structure of D-A conjugated polymers by controlling the interaction between solvents and conjugated polymers. By using the Hansen solubility parameter radius (R_a) to screen different polar and nonpolar solvents, we found that in nonpolar solvents with a larger R_a, the polymer exhibited strong intermolecular aggregation, while in solvents with a smaller R_a, the polymer showed almost no ordered aggregation. During the subsequent film formation process, we extended the crystallization time of the conjugated polymer by controlling the solvent atmosphere. Films prepared in nonpolar solvents with a larger R_a showed the formation of large-sized fibers, exhibiting a mixed orientation of face-on and edge-on. On the other hand, films prepared in solvents with a smaller R_a formed smaller fibers, mainly with an edge-on orientation. In-situ film absorption spectroscopy indicated that the aggregation state of the polymer in nonpolar solvents with a larger R_a could be maintained through a memory effect during the film formation process, while the aggregation behavior of the polymer in solvents with a smaller R_a underwent significant changes. Ultimately, the films prepared in solvents with a larger R_a exhibited higher charge carrier mobility.