Fig. 1. (Color online) Design of neuromorphic synaptic devices and preparation of visual skin. (a) Schematic of biological synapses, neuromorphic visual arrays and material selection. (b) Planar array display. (c) Display in a bent state. (d) Display under outdoor light.

Fig. 2. (Color online) Optical response characteristics of synaptic devices. (a) Schematic diagram of the device under ultraviolet to infrared irradiation. (b) Photoresponse of the IGH-based device to 365 nm light exposure without an external power supply. (c) Light response under 455 to 680 nm illumination. (d) UV absorption of pure ionogels, doped ionogels and heterojunction ionogels. (e) Two cycles at different UV power densities. (f) Heterojunctionogel size selection.

Fig. 3. (Color online) Neuromorphic behaviors of the heterojunctionogel-based device. (a) EPSC responses of ten successive light pulses under different light wave length. (b) PPF index of the device due to varying off spike interval between two consecutive spikes. The inset shows the PPF achieved by two successively applied optical pulses. (c) Real-time plot of synaptic plasticity of the device showing STP and LTP by train of 2 and 11 optical pulses. (d) Influence of the light pulse duration on the EPSCs. (e) Effect of light powers on the EPSCs under a 365 nm light with a frequency of 1 Hz. (f) Stepwise learning behavior of the device.

Fig. 4. (Color online) Demonstration of self-healing and bending properties of ionogel-based optosynaptic devices. (a) Photosynaptic properties of devices before and after shear healing. (b) Optical synaptic properties of devices in plane states and with different curvature.

Fig. 5. (Color online) Mechanism of photothermoelectric effect of heterojunction ionogels. (a) The photothermal effect of local surface plasmon resonance under light results in ion migration within the gel. (b) The change in response photocurrent caused by the change in device temperature over time. (c) Voltage difference-temperature difference curves for Soret effect mechanism. (d) Comparison of photocurrent of the heterojunction, pure and doped ionogels under light illumination.

Fig. 6. (Color online) Neuromorphic visual skin device. (a) Schematic diagram of skin device with light sensing vision. (b) Optical synaptic performance of individual pixels under normal and curved conditions. (c) An optical photograph of a bendable neuromorphic visual skin device attached to human skin. The fist (bend) state before (top) and after (bottom) light. (d) Photoreactivity EPSC for bendable neuromorphic visual skin devices about the number of pulses and the timing.