Vertical Growth of Ultrathin Bi ₂ WO ₆ Nanosheets for Visual Optoelectronic Neuromorphic Devices

ABSTRACT Planar‐grown 2D Bi ₂ WO ₆ is promising for ferroelectric and opto‐synaptic applications, but the fabrication of the device relies on organic solvents, which introduce residues. As a result, the devices show short opto‐synaptic memory and non‐electrically erasable behavior, limiting their suitability for neuromorphic applications. Therefore, developing stable preparation methods for vertical 2D Bi ₂ WO ₆ samples and exploring their applications in low‐power neuromorphic devices are of significant importance. Here, ultrathin Bi ₂ WO ₆ nanosheets with tunable vertical and planar morphologies are synthesized via controlled one‐step chemical vapor deposition (CVD), where vertically aligned configurations enable residue‐free transfer. Building on this, simple two‐terminal Bi ₂ WO ₆ optoelectronic synaptic devices that exhibit an ultralow dark current (∼0.1 pA), a high I _ph/ I _dark ratio (>10 ⁵ ), and long memory retention (∼25 000 s) are fabricated. These devices successfully emulate key synaptic functions, including excitatory postsynaptic currents (EPSC), paired‐pulse facilitation (PPF), and short‐to‐long‐term plasticity (STP‐to‐LTP) transitions under optical stimuli. Critically, optically programmed long‐term potentiation (LTP) and electrically erased long‐term depression (LTD) are achieved with ultra‐low energy consumption below 1 pJ per operation. The Bi ₂ WO ₆ devices, through their optically programmable plasticity and energy‐efficient neuromorphic operation, demonstrate significant potential for next‐generation artificial vision systems, sensing‐memory‐computing integrated architectures, and high‐fidelity neuromorphic hardware.