Photo‐Rewritable Ambipolar Organic Electrochemical Synapses with Bidirectional Optical Plasticity for Adaptive Vision in Aqueous Environments

Emulating biological vision requires aqueous-compatible neuromorphic devices that perform light sensing and complex synaptic dynamics. Organic electrochemical transistors (OECTs), capable of converting ionic signals into electronic current via electrochemical doping, closely mimic biological synaptic signaling. This capability distinguishes them from traditional electronic synapses, which rely purely on electron transport. However, prior OECTs typically require multiple components for bidirectional synaptic potentiation and depression, limiting integration and scalability. Here, we present an ambipolar all-polymer bulk heterojunction vertical OECT that enables light-tunable bidirectional synaptic plasticity while functioning stably in aqueous electrolytes at low operating voltages (≤ 0.4 V). Through photon-modulated electrochemical doping and ambipolar charge transport, the device integrates light sensing, bidirectional synaptic plasticity, and sustained memory (over 130 min) in a single device, mimicking the dual-polarity signaling of retinal bipolar cells. This design allows the transistor to read, write, and erase signals without complex external circuitry. We further demonstrate a vertically integrated optoelectronic synaptic array capable of image recording, selective optical erasure, rewriting, and background denoising, highlighting the feasibility of both global and localized reprogramming. This scalable, light-controlled organic synapse unlocks high-density, biocompatible circuits for artificial retinas and neuromorphic vision.