Tuning Solution Aggregates and Thin Film Polymorphs in Conjugated Polymers via External Electric Field for Field-Effect Transistors

Tailoring polymorphic crystals of π-conjugated semiconducting polymers is crucial for elucidating the structure-optoelectronic property relationship. However, facile and generic strategies for tuning their polymorphs remain a grand challenge. Herein, we report, an effective external electric field (EEF) strategy to adjust polymorphs of poly(3-butylthiophene) (P3BT) in thin film and correlate different polymorphs strongly to their chain conformation and aggregates in solution. Specifically, P3BT without EEF displays a twisted chain conformation and aggregates weakly in solution, yielding sole polymorph II. Interestingly, the EEF induces P3BT chains to a planarized conformation and strengthens the solution aggregates, rendering an efficient polymorph II-to-I transition. The carrier transport properties correlate strongly with their various polymorphs. Such an EEF-induced polymorph transformation is easily exercised to other conjugated polymers. This work demonstrates the robustness of EEF to tailor polymorphs of conjugated polymers and their charge transport properties, contributing to a deep understanding of their crystalline behaviors for diverse optoelectronic applications.