Mimicking Synaptic Plasticity: Optoionic MoS2 Memory Powered by Biopolymer Hydrogels as a Dynamic Cations Reservoir

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 (MoS2)-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 MoS2, emulating synaptic plasticity including sensory, short-term, and long-term memory operation. The SA/MoS2 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 MoS2 bottom face with P(VDF-TrFE), realizing 60 photo-induced multilevel states, and independent conductivity modulation via ferroelectric gating. This Janus SA/MoS2/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.