Fig. 1. Device design and characterization. (a) Biological synapses. (b) Schematic illustration of the artificial synaptic device. (c) and (d) Atomic force microscope image of the topography of CsPbBr3 at different sizes of 2 and 6 μm. (e) Plot showing the transfer characteristics of synaptic transistor with VDS=0.05  V. (f) Room temperature transfer characteristics (I−V curve) of the device at VDS=0.05  V using 450 nm laser light with different powers from 0 to 40 mW.

Fig. 2. PSC response changes under 450 nm light pulse/electrical pulse stimuli with different light power/gate voltage and pulse width and its STP. (a) ΔPSC versus light stimulation pulses of same pulse width (5 s) but different light powers from 10 to 40 mW. (b) ΔPSC versus light stimulation pulses of same light power (30 mW) with different light pulse widths of 1, 2, 10, 15, 20 s. (c) ΔPSC versus 0.8 V gate electrical pulses with different pulse widths from 200 ms to 1 s. (d) ΔPSC versus gate pulses of same pulse width (500 ms) but different pulse amplitudes. (e) ΔPSCs triggered by a pair of 450 nm light pulses (light power of 30 mW, VDS=0.05  V, Δt=100  ms). (f) Paired pulse facilitation index as a function of interspike interval (Δt) varying from 100 ms to 10 s. (g) IPSC triggered by a pair of presynaptic spikes (0.8 V, 1 s, VDS=0.05  V, Δt=1  ms). (h) PPF index as a function of interspike interval (Δt) varying from 1 to 2500 ms.

Fig. 3. Synaptic photocurrent response under different gate biases and schematic diagram of its photocurrent generation mechanism. (a) ΔPSC under single 450 nm light pulse stimuli with a pulse width of 3 s and power of 40 mW at different gate biases (0 V and −1  V) and 0.05 V VDS. (b) Schematic diagram of heterojunction energy band structure and charge transfer under light stimuli and gate biases (0 V or −1  V). (c) ΔPSC under single 450 nm light pulse stimuli with a pulse width of 3 s and light power of 40 mW at different gate biases (−2.2  V and −2.5  V) and 0.05 V VDS. (d) Schematic diagram of heterojunction energy band structure and charge transfer under light stimuli and gate biases (−2.2  V or −2.5  V).

Fig. 4. Controllable LTP and LTD property under optoelectronic collaborative stimuli. (a) ΔPSC response triggered by 40 successive light pulses (30 mW, 1 s) with various frequencies, at VDS=0.05  V and VGS=0  V. (b) Current amplitude gain (A40/A1) versus frequency of light pulse stimuli sequence. (c) Under the VGS=−2.5  V gate bias and VDS=0.05  V, ΔPSC response triggered by 1 min successive 450 nm light pulses (40 mW, 500 ms) with various frequencies. (d) Current amplitude gain (B40/B1) as a function of the frequency of 450 nm light pulse sequence. (e) Optic memory and electrical erasure based on light potentiation and electrical depression. At VDS=0.05  V, 30 consecutive 450 nm light pulses (30 mW, 500 ms) with 816 mHz pulse frequency are followed by 30 consecutive depression electrical spikes at the frequency of 1 Hz (10 mV, 500 ms). (f) LTD/LTP characteristic of the device in weight update for optoelectronic collaborative stimuli, where successive electrical pulses at the frequency of 1 Hz (4 mV, 500 ms) are collaborated with 30 mW 450 nm light off and on.

Fig. 5. Information coding and calculation application of our device. (a) Schematic diagram of Morse code transmission of optical form. (b) ΔPSC response in our device versus the Morse code “BUPT” of optical form, where the light pulse width 2 s is for the dash signal (“−”), 0.5 s is for the dot signal (“·”), and 1 s between the dashed and dotted signals is no light illumination. (c) Schematic diagram and status table of XOR logic operation for our device. (d) ΔPSC response of performing XOR logical operations.

Fig. 6. Simulated perceptual learning capability of our synaptic device on handwritten letter recognition. (a) Simulation structure of the spiking neural network. (b) Handwritten letter image recognition accuracy under different weight changes due to different light powers. (c) Learning output image by different light powers.