Ultrafast Vertical Organic Electrochemical Transistors With Ion‐Permeable Conductive Polymer Top Electrodes

ABSTRACT Organic electrochemical transistors (OECTs) combine mixed ionic‐electronic transport with bulk electrochemical doping to enable high transconductance and low‐voltage operation in aqueous environments, making them attractive for bioelectronics and neuromorphic computing. Vertical OECTs (vOECTs), with channel lengths reduced to tens of nanometers, offer high current densities and compact device footprints, but their performance is fundamentally constrained by ion‐impermeable metal top electrodes that restrict ion injection to slow lateral diffusion pathways. Here, we show that electrochemically stable, ion‐permeable conductive polymers such as poly(benzodifurandione) (PBFDO) offer a powerful alternative to metal top electrodes in vOECTs. By enabling direct vertical ion injection into poly(benzimidazobenzophenanthroline) (BBL) channels, PBFDO yields devices with high current densities (>400 A cm −2 ), large on/off ratios (>10 6 ), and ultrafast switching down to 28 µs, nearly two orders of magnitude faster than equivalent gold‐based vOECTs and among the fastest accumulation‐mode OECTs reported to date. These results establish a new benchmark for OECT speed and underscore the role of ion‐permeable electrodes in overcoming the coupling between electronic and ionic transport in vertical architectures.