High-performance n-type organic mixed ionic-electronic conductors enabled by strong cation-π interactions

Abstract Conjugated polymers that can efficiently transport both ionic and electronic charges have shown broad applications in next-generation optoelectronic, bioelectronic, and energy storage devices. To date, almost all the conjugated polymers have hydrophobic backbones, which impedes efficient ion diffusion/transport in aqueous media. Here, we design and synthesize a novel hydrophilic polymer building block, 4a-azonia-naphthalene (AN). Because of the strong electron-withdrawing ability of AN, the traditional p-type polymer, thiophene diketopyrrolopyrrole (TDPP) polymer, turns into an n-type polymer. More importantly, AN enhances the hydrophilicity and ionic-electronic coupling of the polymer, leading to a fast device response (1.00 ms/0.18 ms) and a high figure-of-merit (μC*) of 62.3 F cm −1 V −1 s −1 in organic electrochemical transistor (OECT). We find that cationic aromatics exhibit interesting cation-π interactions, leading to smaller π-π stacking distances and interesting ion diffusion behavior. Our work demonstrates that ionic polymer backbones can provide efficient ionic-electronic coupling and charge transport for organic electronics working in aqueous media.