Intrinsically Stretchable n-Type Polymer Semiconductors through Side Chain Engineering

The development of intrinsically stretchable n-type polymer semiconductors is highly desirable for various wearable and implantable electronics. However, very few studies have reported high-performance stretchable n-type conjugated polymers by molecular engineering. Herein, high electron mobility preservation under high stretch-strains is achieved by changing the type of grafted side chains as well as increasing the density of grafted side chains. A series of bis(2-oxoindolin-3-ylidene)-benzodifuran-dione (BIBDF)-based conjugated polymers with different side chains including alkyl chains and hybrid siloxane-based chains was synthesized to investigate the structure–property relationship. The experimental results demonstrated that replacing branched alkyl side chains with linear hybrid siloxane-based side chains and increasing the density of side chains greatly reduced the crystallinity of films and improved the flexibility of polymer chains. The resulting polymer CSi-PBIBDF showed significantly enhanced mechanical properties while maintaining high electron transport properties. Surprisingly, the electron mobility parallel to the stretching direction for the CSi-PBIBDF thin film reached 0.21 cm2 V–1 s–1 at 100% strain, which is higher than that of the unstretched state, attributed to the stretch-induced alignment of the polymer chain. The current study demonstrated that systematic side chain engineering is extremely important to achieve high-performance stretchable n-type polymer semiconductors.