Mimicking Synaptic Plasticity: Optoionic MoS ₂ Memory Powered by Biopolymer Hydrogels as a Dynamic Cations Reservoir

Abstract Neuromorphic devices are emerging as key components for next‐generation computing, driven by the rapid growth of digital technology. To meet growing demand for energy‐efficient logic operations, photonic synaptic devices have become a focal point of interest. Here, a novel molybdenum disulfide (MoS ₂ )‐based synaptic memory field‐effect transistor (FET) is presented, exploiting the photo‐induced ionic gating effect through Janus functionalization with ion‐conductive sodium alginate (SA) and ferroelectric poly(vinylidene fluoride‐co‐trifluoroethylene) [P(VDF‐TrFE)]. The integration of SA as a dynamic cations reservoir enables ion migration and corresponding modulation of persistent photoconductivity on MoS ₂ , emulating synaptic plasticity including sensory, short‐term, and long‐term memory operation. The SA/MoS ₂ FET demonstrates over eight multilevel states adjustable by light irradiation conditions. The device also exhibits excellent visible‐range photodetection (455–680 nm), with a high photoresponsivity of 20 kA W ⁻¹ and a fast response time of 120 ms under 20 V gate bias and 680 nm LED illumination. Further functionality is endowed by decorating MoS ₂ bottom face with P(VDF‐TrFE), realizing 60 photo‐induced multilevel states, and independent conductivity modulation via ferroelectric gating. This Janus SA/MoS ₂ /P(VDF‐TrFE) configuration supports near‐infrared detection governed by ferroelectric polarization. These findings highlight the transformative potential of integrating sustainable biopolymers with 2D materials for environmental‐friendly neuromorphic 2D optoelectronics.