Conjugated Carbon Cyclic Nanoring as Additives for Intrinsically Stretchable Semiconducting Polymers
Molecular additives are often used to enhance dynamic motion of polymeric chains, which subsequently alter the functional and physical properties of polymers. However, controlling chain dynamics of semiconducting polymer thin films, and understanding the fundamental mechanisms of such changes is a new area of research. Here, cycloparaphenylenes (CPPs) are used as conjugated molecular additives to tune the dynamic behaviors of diketopyrrolopyrrole-based (DPP-based) semiconducting polymers. It is observed that the addition of CPPs results in significant improvement in the stretchability of the DPP-based polymers without adversely affecting their mobility. Specifically, the DPP-based polymer thin films originally form cracks at 15％ strain, while the addition of 5 wt％ CPP improves the stretchability to 105％ strain, which arises from enhanced polymer dynamic motion and reduced long-range crystalline order. The polymer films retained their fiber-like morphology and short-range ordered aggregates, which lead to high mobility. Fully stretchable transistors are subsequently fabricated using CPP/semiconductor composites as active layers. These composites are observed to maintain high mobilities when strained and after repeated applied strains. Interestingly, CPPs are also observed to improve contact resistance and charge transport of the fully stretchable transistors. ln summary, the above results collectively indicated that controlling the dynamic motion of polymer semiconductors proved to be an effective way to improve its stretchability.