Backbone Engineering of Bithiophene Imide Dimer-Based Polymeric Mixed Ionic-Electronic Conductors for High-Performance n-Type Organic Electrochemical Transistors

Polymeric mixed ionic-electronic conductors (PMIECs) are gaining significant attention due to their potential applications in organic electrochemical transistors (OECTs). However, the performance of n-type OECTs still lags behind that of their p-type counterparts. Here, the structure-performance correlation of fused bithiophene imide dimer (BTI2)-based PMIECs is systematically investigated with the backbone evaluation from acceptor-strong donor (A-SD) to acceptor-donor (A-D), to acceptor-weak donor (A-WD), to acceptor-weak acceptor (A-WA), and finally to A-A structures. Compared to other PMIECs, the A-A backbone-based PMIEC PBTI2g-BTI features the most suppressed lowest unoccupied molecular orbital energy level, a highly planar backbone, and superior n-type electrochemical dopability. Consequently, polymer PBTI2g-BTI delivers an exceptional unipolar n-type OECT performance with a high electron mobility of 0.25 cm² V⁻¹ s⁻¹ and a remarkable µC^* value of 63.79 F cm⁻¹ V⁻¹ s⁻¹, both of which are significantly higher than those of other types of PMIECs. This study demonstrates that the A-A backbone strategy is an effective approach to developing high-performance n-type PMIECs for applications in OECTs.