The Regulating Role of Ionic Species in Organic Electrochemical Transistors: Toward High-Performance Bioelectronics.

Organic electrochemical transistors (OECTs) have emerged as highly promising platforms for next-generation bioelectronic interfaces, fundamentally driven by their unique mixed ionic-electronic conduction and volumetric doping mechanisms. Despite significant progress in understanding electronic transport, the intricate dynamics of ion transport-encompassing interfacial double-layer kinetics and complex electrolyte-channel interactions-continue to constrain ultimate device performance and introduce profound physical complexities. To address this critical gap, this review provides a systematic overview of the regulatory roles of ionic species in OECTs, bridging microscopic ion dynamics with macroscopic device performance. First, the theoretical foundations of ion transport kinetics and interfacial processes are discussed. Next, comprehensive molecular and architectural engineering strategies for optimizing ion transport, including polymer backbone modulation, side-chain tailoring, and the integration of functional electrolyte systems, are systematically examined. This is followed by an exploration of the practical manifestations of these precisely managed ionic effects in advanced applications, specifically highlighting broad biosensing capabilities and biomimetic neuromorphic computing. Finally, the review concludes by identifying persistent challenges, notably the intrinsic trade-off between crystallinity and ionic permeability, and outlines potential future trajectories for the development of robust, high-performance ion-regulated organic bioelectronics.