n‐Type Organic Mixed Ionic‐Electronic Conductors for Organic Electrochemical Transistors

n‐Type organic electrochemical transistors (OECTs) are fundamental building blocks of biosensors and complementary circuits along with p‐type. Yet, their development has been lagging behind their p‐type counterparts since first emergence in 2016. The key component of an OECT is the channel material, which is an organic mixed ionic‐electronic conductor (OMIEC), that dictates the function and performance of the OECT via interactions with electrolyte ions. OMIECs of OECTs are benchmarked by the product of charge‐carrier mobility ( μ ) and volumetric capacitance ( C * ), μC * . Significant progress is made for the development of novel n‐type OMIECs, with best μC * now reaching 180 F cm −1 V −1 s −1 . This review elucidates such material development progress of n‐type OMIECs with emphases on the underlying molecular design strategies and structure‐property relationships. Furthermore, the operational stability of channel materials and the applications of n‐type OECTs are also discussed to offer readers a comprehensive view of the field. Finally, current limitations are discussed along with outlook.