Control of Donor-Acceptor Conjugated Polymer Crystallization for Optimized Film Structures in Organic Transistors

Donor-acceptor (D-A) conjugated polymers are promising materials for organic transistors including organic field-effect transistors (OFETs) and organic electrochemical transistors (OECTs). The aggregated structure of D-A conjugated polymer films, which strongly depends on the crystallization process, is crucial for the device performance. However, the crystallization of D-A conjugated polymers is complicated during solution processing, and the optimal film structure is various in different applications. Therefore, it is significantly important to reveal the relationship between the processing conditions and the resulting aggregated structures. This review provides a systematic understanding of how to control the aggregated structure of D-A conjugated polymer films from the fundamental mechanisms of polymer crystallization. We first discuss the possible nucleation and growth mechanisms of D-A conjugated polymers based on traditional theories or models and current findings. Then, recent progress in controlling the structure of D-A conjugated polymer films for OFETs and OECTs is reviewed. D-A conjugated polymers generally adopt chain-extended crystallization due to their strongly rigid backbone, which makes homogeneous nucleation difficult. A common strategy to control the aggregated structure of D-A conjugated polymer films is to manipulate the heterogeneous nucleation process by tuning the pre-aggregation. Besides, the effect of the crystallization rate and complicated conditions on the aggregated structure of D-A conjugated polymer films is also discussed. Finally, a concise summary is provided, followed by some current challenges in controlling the aggregated structure of D-A conjugated polymer films.