Cyano‐Functionalized n‐Type Polymer with High Electron Mobility for High‐Performance Organic Electrochemical Transistors

Abstract n‐Type organic mixed ionic–electronic conductors (OMIECs) with high electron mobility are scarce and highly challenging to develop. As a result, the figure‐of‐merit ( µC *) of n‐type organic electrochemical transistors (OECTs) lags far behind the p‐type analogs, restraining the development of OECT‐based low‐power complementary circuits and biosensors. Here, two n‐type donor–acceptor (D–A) polymers based on fused bithiophene imide dimer f‐BTI2 as the acceptor unit and thienylene–vinylene–thienylene (TVT) as the donor co‐unit are reported. The cyanation of TVT enables polymer f‐BTI2g‐TVTCN with simultaneously enhanced ion‐uptake ability, film structural order, and charge‐transport property. As a result, it is able to obtain a high volumetric capacitance ( C *) of 170 ± 22 F cm −3 and a record OECT electron mobility (μ e,OECT ) of 0.24 cm 2 V −1 s −1 for f‐BTI2g‐TVTCN, subsequently achieving a state‐of‐the‐art µC * of 41.3 F cm −1 V −1 s −1 and geometry‐normalized transconductance ( g m,norm ) of 12.8 S cm −1 in n‐type accumulation‐mode OECTs. In contrast, only a moderate µC * of 1.50 F cm −1 V −1 s −1 is measured for the non‐cyanated polymer f‐BTI2g‐TVT. These remarkable results demonstrate the great power of cyano functionalization of polymer semiconductors in developing n‐type OMIECs with substantial electron mobility in aqueous environment for high‐performance n‐type OECTs.