Surface Photovoltage-Driven Hour-Scale Plasticity in Self-Powered Perovskite Optoelectronic Synapse

Conventional perovskite-based artificial synapses have successfully emulated key features of biological plasticity but typically require high-intensity, repetitive electrical or optical stimulation under external bias, limiting their energy efficiency, scalability, and temporal relevance. Here, we demonstrate a self-powered, bias-free optoionic synapse based on a MAPbI 3 thin film, whose surface photovoltage (SPV) response exhibits hour-scale plasticity triggered by a single short-duration illumination pulse. A 30 s flash of AM 1.5G light (50–150 mW/cm 2 ) induces directional migration of iodide vacancies and methylammonium cations toward the illuminated interface, steepening interfacial band bending and enhancing the SPV by a factor of 2.3–4.5. The potentiated state persists for several hours in darkness and relaxes logarithmically, governed by thermally activated ionic back diffusion. Repeated stimulation leads to dose-dependent fatigue, characterized by reduced SPV gain, shorter retention, and slightly lowered activation barriers─indicative of ion reservoir depletion or lattice relaxation. These results establish a light-programmable, analogue synapse that operates without any electrical bias, offering a compact and energy-autonomous platform for mimicking long-term plasticity in neuromorphic and adaptive optoelectronic systems.