Unraveling Ion Transport in Hydrogel-Electrolyte Organic Electrochemical Transistors

Hydrogel electrolytes are promising solid-state candidates for organic electrochemical transistors (OECTs), offering superior stability and independent gating capabilities. However, their integration was often hindered by slow ion transport and inferior device response speeds. Through molecular dynamics (MD) simulations, we resolve the atomic-scale ion dynamics at the interface between a polyvinyl alcohol (PVA) hydrogel and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) channel. Results reveal a sequential mechanism: upon field application, Na⁺ ions migrate through the hydrated PVA matrix, being captured by PSS^- sulfonate groups at the electrolyte-channel interface, and subsequently infiltrate the PEDOT:PSS film, during which the ion solvation shell evolves from water-dominated to PSS^--coordinated. Guided by these mechanistic insights, we engineered a zwitterionic double-network hydrogel by incorporating poly(sulfobetaine methacrylate) (PSBMA), which effectively disrupts PVA crystallinity and enhances interfacial hydration. This tailored electrolyte reduces OECT response time by 46%, achieving switching kinetics comparable to those of liquid electrolytes. This work deciphers the fundamental ion dynamics in hydrogel-electrolyte OECTs and establishes a simulation-guided paradigm for designing high-performance solid-state bioelectronics.