Regiochemistry and Side-Chain Engineering Enable Efficient N-Type Mixed Conducting Polymers

Abstract

Developing high-performance n-type organic mixed ionic-electronic conducting (OMIEC) polymers with simple structural motifs is still challenging. We show that high-performance, low-threshold-voltage n-type OMIEC polymers can be achieved using a simple diketopyrrolopyrrole unit flanked by thiazole groups, which is functionalized with glycolated side chains. Interestingly, the regiospecific sp²-N position in the repeating unit's thiazole governs the polymer chains' solvation and molecular packing. This specific backbone chemistry enhances conjugation efficiency, reduces trap density, and improves electrochemical doping efficiency. Moreover, systematic variation of glycolated side-chain lengths induces a sequential shift in molecular orientation—from edge-on through bimodal to face-on preferential alignment. This structural evolution achieves optimized ionic-electronic transport balance, resulting in exceptional device metrics: a geometrically normalized transconductance of 31.9 S cm⁻¹, a figure-of-merit µC* of 96.3 F cm⁻¹ V⁻¹ s⁻¹, and a threshold voltage of 0.31 V, positioning these materials among the highest-performing n-type OMIECs. An organic complementary inverter made from the optimized n-type OMIEC polymer and a reported p-type polymer exhibits a voltage gain of 198 V V⁻¹, effectively amplifying the ECG signal and enhancing signal quality. This work establishes structure-property guidelines for designing bioelectronic n-type OMIECs.