Switching p-type to high-performance n-type organic electrochemical transistors via doped state engineering

Abstract High-performance n-type organic electrochemical transistors (OECTs) are essential for constructing OECT-based logic circuits and enhancing the sensitivity of OECT-based sensors. However, the performances of n-type OECTs lag far behind that of the p-type ones due to the lack of effective molecular design strategies. Conventional wisdom posits that the LUMO energy level dictates the n-type performance. Herein, we show that engineering the doped state of conjugated polymers is more critical for n-type OECT polymers. By balancing more charges to the donor moiety, we could effectively switch a typical p-type polymer to high-performance n-type OECT materials. Based on this concept, the new polymer, P(gTDPP2FT), exhibits a record high n-type OECT performance with µC* of 54.8 F cm− 1 V− 1 s− 1. The polymer also shows a record n-type OECT electron mobility of 0.35 cm2 V− 1 s− 1, leading to a fast response speed of τon/τoff = 1.75/0.15 ms. DFT calculations and comparison studies show that the switching mechanism of the charge transport type is primarily due to the more uniformly distributed charges, stabilized negative polaron, and enhanced backbone planarity at negatively charged states. Unlike conventional molecular design strategies mainly focusing on lowering the lowest unoccupied molecular orbital (LUMO) level of the neutral polymers, our work highlights the critical role of understanding and engineering the polymer doped states.