Dual‐Wavelength Photoelectrochemical Synapse for Spectral Sensing and Synaptic Plasticity

ABSTRACT Most artificial devices decouple sensing from computing, necessitating external circuits or multi‐device architectures. Here, we present a dual‐mode photoelectrochemical (PEC) synapse based on violet phosphorus (VP) and ZnO that integrates photocurrent‐based optical encoding (current vs. time mode) and potential‐based synaptic plasticity (open‐circuit potential mode) within a single two‐electrode cell. In I‐t mode, 350 nm (ZnO‐dominated) gives −3.36 µA cm ⁻² negative current, 450 nm (VP‐dominated) switches to +0.0075 µA cm ⁻² positive current. In OCP mode, 350 nm induces short‐term plasticity (STP) characterized by an OCP shift from 125 to 248 mV, which mimics activity‐dependent learning, while 450 nm triggers long‐term plasticity (LTP), featuring a stable OCP shift of −1.0 ± 0.1 mV and a retention half‐life (τ _LTP ) of 1130 s for non‐volatile memory. This dual functionality originates from a wavelength‐competitive proton‐writing mechanism, wherein proton diffusion kinetics (under 350 nm) and defect‐mediated proton trapping (under 450 nm) are synergistically modulated at the VP/electrolyte interface. Operating in aqueous medium at zero bias, this PEC synapse provides a compact platform that unifies optical sensing and neuromorphic plasticity, offering potential for biomimetic sensory systems.