Supplementary Material

See the supplementary material for the experimental methods, the preparation process of CuInP2S6-MoS2 vertical heterojunction using an all-dry method, XPS spectra of the monolithically oxidized MoS2 samples, AFM height image of graphene electrode, the endurance cycle measure-ment, performance of optical synapses under different light powers, dif-ferent illumination times, and different numbers of light pulses.