Solution-Processed 2D Transition Metal Dichalcogenide Networks for Scalable, Flexible Photosynaptic Device Arrays

2D transition metal dichalcogenides (TMDCs) have shown promise as a class of optoelectronic material for flexible photosynaptic devices. However, widespread use of 2D TMDCs has been limited because producing high-quality, large-scale films on flexible substrates has still been challenging. Herein, we propose a facile solution processing strategy to realize large-scale arrays of flexible photosynaptic devices based on 2D TMDCs. Bulk molybdenum disulfide (MoS2) crystals were first electrochemically exfoliated into few-layer nanosheets using molecular intercalants, followed by dispersion in isopropyl alcohol for spin coating on flexible substrates. Large lateral size of the nanosheets along with good wettability of the dispersion enabled the formation of continuous MoS2 nanosheet networks for scalable device fabrication. Sulfur vacancies within the MoS2 channel served as trapping sites for photogenerated carriers and supported photocurrent retention characteristics needed to mimic synaptic functions. The device array successfully demonstrated reinforcement learning capabilities for image recognition under repeated optical pulse signals. Finally, the optoelectronic performance was fairly stable under mechanical bending because devices did not crack or delaminate from the substrate.