Polythiophenes for High‐Performance N‐type Organic Electrochemical Transistors

Abstract N‐type organic electrochemical transistor (OECT) materials play a critical role in building low‐power complementary circuits and advanced biosensors. However, current n‐type OECT materials are usually based on complicated fused aromatics and cannot simultaneously achieve high performance and good stability. Despite a few design strategies for n‐type polythiophene‐based organic field‐effect transistor (OFET) materials, they cannot be directly applied to OECT materials which work in highly doped states. Here, it is reported that polythiophenes, which always show p‐type OECT behaviors, can be designed and converted to high‐performance n‐type OECT materials by a synergy of introducing electron‐withdrawing (EW) groups, controlling polaron delocalization, and tuning molecular packing. Two isomeric n‐type polythiophene derivatives, o‐CNgTVT‐2FT and i‐CNgTVT‐2FT are designed, which show interesting and distinct OECT properties. o‐CNgTVT‐2FT exhibits excellent n‐type OECT performance with a remarkable figure of merit (µC^*) of 100.0 F cm⁻¹ V⁻¹ s⁻¹ while keeping an outstanding current retention of 93.6% after 1000 switching cycles in the air. The high performance can be largely attributed to its more delocalized and stabilized negative charges, efficient 3D charge transport channels, and favorable film morphology. The work highlights that without complex fused aromatic rings, carefully designed polythiophene polymers can also be used for high‐performance and stable n‐type OECTs.