Tailoring Multiscale Crystalline Structures in Conjugated Polymers: Bridging Fundamental Insights and Applications in Organic Field-Effect Transistors

Conspectus π-Conjugated polymers are a class of semirigid macromolecules composed of unsaturated building blocks, where π-electron delocalization along the polymer backbones imparts exceptional optoelectronic properties. The charge transport in these polymers depends on intrinsic molecular structures as well as microstructural features, such as chain conformation, polymorphism, crystal orientation, and phase separation across solid-state length scales. Despite significant advancements in synthetic methodologies and iterative molecular design, progress in controlling the crystallization behavior and microstructural formation of conjugated polymers remains relatively limited. This limitation arises primarily from the distinct rigid backbone and flexible side chains and weak, complex interactions. Therefore, effectively controlling the crystallization behavior of conjugated polymers is essential to unravel the intricate relationship between their microstructure and device performance and to enable their deployment in optoelectronic applications. In this Account, we highlight our recent efforts to control and elucidate the formation mechanisms of three important and representative microstructures across distinct levels: polymorphism (interchain packing), crystal orientation (lamellar packing), and multicomponent cocrystallization (multicomponent phase behavior), and to investigate their impact on charge-transport properties. Polymorphism is one of the most fundamental structural features of conjugated polymers; understanding the formation and transformation mechanisms of polymorphs is conducive to elucidate and control more complex structures. Using poly(3-alkylthiophene)s (P3ATs) and poly(3-alkylselenophene)s (P3ASs) as model systems, we demonstrated the formation of distinct polymorphs and their reversible transformations based on differences in thermodynamic stability. Subsequently, the crystalline orientation of representative donor–acceptor (D–A) copolymers (e.g., edge-on and face-on) is controlled by regulating the polymer–solvent and polymer–polymer interactions from a solution-aggregation point of view, which directly impacts charge carrier transport. Finally, we clarify how the second component influences the crystallization of conjugated polymers in multicomponent systems. In conjugated P3AT-based block copolymers (BCPs), two fundamental phase behaviors, cocrystallization and microphase separation, are effectively tuned by modulating the interactions and compatibility between distinct polymer blocks. Furthermore, when inorganic nanocrystals are introduced as secondary components, the conjugated polymers and nanocrystals self-assemble into hierarchical one-dimensional organic–inorganic nanocomposites with high aspect ratios, offering promising potential for diverse applications in optoelectronics, sensors, and catalysis. Precise customization of the microstructures of conjugated polymers is important for establishing the structure–property relationship. This Account summarizes our recent progress in controlling specific important microstructures in representative semirigid conjugated polymers utilizing the dynamic characteristics of polymer crystallization. The principles gained from these specific microstructures can be extended to diverse microstructures in other conjugated polymers, thereby promoting their application in high-performance optoelectronic devices.