Large Surface Photovoltage of WS₂/MoS₂ and MoS₂/WS₂ Vertical Hetero-bilayers

Abstract

Hetero-bilayers,\ncomposed of transition metal dichalcogenide (TMD)\nmonolayers of MoS₂ (1L-MoS₂) and 1L-WS₂, are grown on Al₂O₃ substrates through sulfurization\nof pre-deposited metal thin films. A very smooth surface morphology\nand the uniform contact potential difference (CPD) maps show that\nhigh-quality homogeneous TMD layers are obtained. The light-induced\nCPD change, that is, surface photovoltage (SPV), of the samples is\ninvestigated. A record high SPV is measured under 532 nm illumination\nwith a power density of 13 mW/cm² from the hetero-bilayers,\nwith values of 800 mV for 1L-WS₂/1L-MoS₂ and\n−790 mV for 1L-MoS₂/1L-WS₂. Band diagrams\nare proposed to explain the observed CPD and SPV characteristics.\nThe power dependence of the SPV demonstrates that the measured values\nrepresent the expected open-circuit voltage of the hetero-bilayers.\nThe obtained results suggest that optimal growth and proper contact\nformation with the TMD vertical hetero-bilayers will enable high-efficiency\nultrathin photovoltaic devices.