Air-stable synaptic devices based on bismuth triiodide and carbon nanotubes

Artificial synaptic devices with the functions of emulating important biological synaptic behaviors are playing an increasingly important role in the development of neuromorphic computing systems. Single-walled carbon nanotubes (SWCNTs) with excellent electrical properties and high stability have been studied as active materials for synaptic devices. However, the performance of optical synaptic devices (OSDs) based on pure SWCNTs is limited by the weak light absorption property. Herein, bismuth triiodide (BiI₃), an environmentally stable and friendly optoelectronic material, is firstly combined with SWCNTs to fabricate OSDs with decent properties of perceiving and memorizing optical information. The OSDs can exhibit typical synaptic behaviors including excitatory postsynaptic current, paired-pulse facilitation, and short/long-term memory. Distinctively, the photo-response of the OSD is independent of pulse light wavelength in the range of 365 to 650 nm, different from most of the previously reported OSDs, which usually have wavelength-dependent photo-response. Temperature- dependent photo-response behaviors of the devices are investigated. Importantly, the OSD without encapsulation holds good excitatory post-synaptic current (EPSC) behavior after being stored in the ambient environment for 170 days, indicating reliable environmental stability. Furthermore, an OSD array with nine synaptic devices is employed to mimic the human visual perception and memory functions. These results suggest the feasibility of BiI₃/SWCNTs-based OSDs for the simulation of human visual memory.