Harnessing Thin-Film Polymorphism via Regulating Conjugated Polymer–Solvent Interactions for Organic Field-Effect Transistors

Tailoring the polymorphism of conjugated polymers is a promising strategy to enhance the performance of optoelectronic devices. However, a comprehensive understanding of the formation and transformation mechanisms of these polymorphisms remains limited. Herein, we correlate, for the first time, thin-film polymorphisms of poly(3-hexylselenophene) (P3HS) with their solution-state polymer-polymer and polymer-solvent interactions by quantifying the second virial coefficient (A₂). P3HS exhibits weak aggregation in toluene, where A₂ is positive and polymer-solvent interactions dominate. The fast toluene evaporation kinetically traps these weak aggregates in polymorph I in the film. In contrast, P3HS aggregates strongly in p-xylene, where A₂ is negative and polymer-polymer interactions prevail. The slower evaporation of p-xylene promotes the formation of polymorph II. P3HS polymorphs greatly affect their charge transport characteristics, with higher mobility observed in polymorph I. This study highlights a direct connection among different molecular interactions, solution aggregates, and thin-film polymorphisms of conjugated polymers.