Artificial synaptic devices hold great potential in building neuromorphic computers. Due to the unique morphological features, two-dimensional organic semiconductors at the monolayer limit show interesting properties when acting as the active layers for organic field-effect transistors. Here, organic synaptic transistors are prepared with 1,4-bis ((5’-hexyl-2,2’-bithiophen-5-yl) ethyl) benzene (HTEB) monolayer molecular crystals. Functions similar to biological synapses, including excitatory postsynaptic current (EPSC), pair-pulse facilitation, and short/long-term memory, have been realized. The synaptic device achieves the minimum power consumption of 4.29 fJ at low drain voltage of −0.01 V. Moreover, the HTEB synaptic device exhibits excellent long-term memory with 10⁹ s EPSC estimated retention time. Brain-like functions such as dynamic learning-forgetting process and visual noise reduction are demonstrated by nine devices. The unique morphological features of the monolayer molecular semiconductors help to reveal the device working mechanism, and the synaptic behaviors of the devices can be attributed to oxygen induced energy level. This work shows the potential of artificial neuroelectronic devices based on organic monolayer molecular crystals.

Organic crystals, especially ultra-thin two-dimensional (2D) ones such as monolayer molecular crystals, are fragile and vulnerable to traditional vacuum deposition. Up to now, most of the methods reported for fabricating organic field-effect transistors (OFETs) with top-electrodes on the 2D molecular crystals are based on mechanical-transfer method. Nondestructive method for large scale in-situ electrode deposition is urgent. In this work, the silver mirror reaction (SMR) is introduced to construct top-contact electrodes on 2D organic crystalline thin films. OFETs based on bilayer crystalline films with solution-processed silver electrodes show comparable performance to devices with transferred gold electrodes. In addition to that, OFETs with SMR fabricated silver electrodes show lower contact resistance than the ones with evaporated silver electrodes. Furthermore, the temperature under which SMR electrodes annealed is relatively low (60 ℃), making this approach applicable to varies of organic semiconductors, such as spin-coated polymer films, vacuum evaporated films, 2D and even monolayer crystalline films. Besides, OFETs with sub-micrometer channel width and 25 μm channel length are realized which might find practical application in the ultra-small pixel mini/micro-LEDs.