Fig. 1. Device structure diagram and optical properties [all tests in this figure were done in vacuum (10^-5 Torr)]. (a) Schematic diagram of the device structure without interface protection; (b) current-voltage (I-V) curves measured under darkness, illumination (9 µW·cm^-2) and post-illumination conditions; (c) EPSC under continuous illumination (500 ms, 16 mW·cm^-2)

Fig. 2. EPSC behavior of uninterface protected devices (all tests in this figure were done in air). (a) Typical photocurrent generation and attenuation characteristics under 365 nm UV light irradiation; (b) EPSC behavior triggered by a pair of light pulses; (c) EPSC behavior triggered by multiple pairs of light pulses

Fig. 3. Device structure, film surface morphology, and electrical properties. (a) Device structure diagram; (b) optical image of the film; (c) cross-polarized optical image of the film; (d) AFM image; (e) I-V curves in darkness and under irradiation (101 µW/cm² and 210 µW/cm²); (f) EPSC behaviors triggered by different light intensities (10.8 µW/cm², 101 µW/cm², 210 µW/cm², 360 µW/cm², and 546 µW/cm²); (g) photocurrent under different light intensities fitted as a function of optical power; (h) testresults of I-V curve (dark) repeatability performance; (i) testresults of single light response repeatability performance

Fig. 4. Optical synaptic plasticity of devices. (a) Typical photocurrent generation and attenuation characteristics under 365 nm UV light irradiation; (b) EPSC behavior triggered by a pair of light pulses; (c) fitting curve of PPF ratio varying with spike time interval (Δt); (d) EPSC behaviors of single pulse, a pair of pulses, and ten pairs of pulse; (e) EPSC for different pulse widths (200 ms, 400 ms, 600 ms, and 700 ms) (the illustration shows the relationship between peak current value and pulse width); (f) normalized currents of three devices

Fig. 5. Device response under continuous light pulses. (a) EPSC behavior triggered by 26 presynaptic pulses; (b) synaptic weight change as a function of number of pulses; (c) multiple pulses at different frequencies; (d) normalized currents under stimulation of 0 nm, 5 nm, and 7 nm devices under single pulse; (e) normalized currents under stimulation of 0 nm, 5 nm, and 7 nm devices under double pulses; (f) normalized current map under stimulation of 0 nm, 5 nm, and 7 nm devices under ten pulses