Polyvinylalcohol (PVA)-Assisted Exfoliation of ReS2 Nanosheets and the Use of ReS2–PVA Composites for Transparent Memristive Photosynapse Devices

Two-dimensional (2D) transition metal dichalcogenides (TMDs) have attracted significant attention for their outstanding optoelectrical properties. Unlike most TMDs with layer-dependent photoresponsivity, rhenium disulfide (ReS2) shows excellent thickness-independent photoresponsivity. Herein, we show a surfactant-free polyvinyl alcohol (PVA)-assisted exfoliation method for 2D-TMDs in aqueous solution and a transparent photosensitive memristor synapse device based on ReS2 nanosheets composited with PVA. ReS2 nanosheets are obtained via PVA-assisted exfoliation. After exfoliation, the ReS2–PVA dispersion solution is spin-coated on a substrate and dried to form a nanocomposite film without additional processing. Transparent memristors are then fabricated on plastic or glass substrates to demonstrate the applicability of the ReS2–PVA film. The devices show "write once, read many" memory behavior with a high ON/OFF current ratio (1.0 × 104 at 0.5 V) during electrical operation. In the high resistive state, synaptic functions with long-term memory behavior are successfully mimicked by applying photonic stimuli to the transparent ReS2–PVA memristors. The excitatory postsynaptic current stimulated by the photosignal is gradually reduced by electric stimuli. The proposed PVA-assisted exfoliation method is cost-effective, environmentally friendly, and applicable to various TMD nanomaterials. Furthermore, the ReS2–PVA nanocomposite film obtained via a simple solution-based process demonstrates excellent photosynaptic behavior.