Ionic‐Electronic Coupling Modulation Induced by Nanofibrous Phase Separation for Synaptic Organic Electrochemical Transistors

ABSTRACT Organic electrochemical transistors (OECTs) represent a promising platform for neuromorphic computing, owing to their unique ability to achieve non‐volatile memory under low‐voltage operation. The achievement of biologically relevant synaptic functionalities within OECTs remains challenging due to uncontrolled ionic‐electronic coupling, limited device stability, and fabrication complexity. Herein, we report synaptic OECTs based on polymer blends of the ion‐permeable semiconductor (Pg2T‐T) and the ion‐blocking polymers (PMMA, PS), which are designed to modulate ionic diffusion within the transistor channel. Morphological and electrochemical characterizations demonstrate that the incorporation of these blocking polymers induces nanofibrous phase separation, resulting in continuous Pg2T‐T nanofibers that facilitate electronic transport, interspersed with PMMA‐rich domains serving as physical barriers to ion migration. Based on the systematic evaluation of OECT transistor and synapse performances, we identified an optimal Pg2T‐T to PMMA composition ratio of 1:2, which yields significantly enhanced synaptic behaviors, including excitatory postsynaptic current (EPSC), tunable paired‐pulse facilitation and depression (PPF/PPD), as well as stable long‐term potentiation and depression (LTP/LTD) across multiple writing/erasing cycles. Moreover, by integrating the device into a neuromorphic system based on the Fashion‐MNIST dataset, achieving a classification accuracy of 80.41%, which surpassed the ideal synapse baseline, attributed to the beneficial stochasticity of physical weight updates. These results highlight a scalable material strategy for high‐robust synaptic emulation in OECTs, offering a promising foundation for future bioinspired neuromorphic hardware.