Fig. 4: Switchable bulk photovoltaic effect in 2D 3R-WS2 based retinomorphic device.
From: Reconfigurable and nonvolatile ferroelectric bulk photovoltaics based on 3R-WS2 for machine vision
a Schematic diagram and optical microscope image illustrating the crossbar structure of the graphene/3R-WS2/graphene retinomorphic device. The blue and red spheres represent the sulfur and tungsten atoms for the crystal structure, respectively. The purple arrows indicate the direction of spontaneous polarization. b Cross-sectional TEM image and corresponding EDS element mapping of the graphene/3R-WS2/graphene interfaces. c, The characteristics I-V curve of positive and negative photovoltaic behavior under different poled voltage. d, e Illuminated I-V characteristics measured after applying positive and negative poling voltage to the graphene/3R-WS2/graphene retinomorphic device initialized by 2 V and −2 V pulses (pulse width: 0.5 ms), respectively and the black dotted arrow illustrates the different polarization direction. The excitation light wavelength is 623 nm and the light intensity is 20 mW cm−2. f The energy band diagrams of graphene/3R-WS2/graphene in different polarization states under illumination, highlight the influence of ferroelectric polarization on the generation and movement of photogenerated carriers. The top and bottom graphene electrodes are represented by gray atoms, and the built-in electric fields are represented by orange arrows.
