Large variations in both dark- and photoconductivity in nanosheet networks as nanomaterial is varied from MoS2 to WTe2

Abstract

We have used solution processing techniques to fabricate thin-film networks of nanosheets of six different transition metal dichalcogenides; MoS₂, MoSe₂, MoTe₂, WS₂, WSe₂ and WTe₂. We have measured both the dark conductivity and the photoconductivity under broad band illumination in the intensity range from 0–1500 W m⁻². The dark conductivity varied from ∼10⁻⁶ S m⁻¹ for MoS₂ to ∼1 S m⁻¹ for WTe₂, with an apparent exponential dependence on bandgap. All materials studied show photocurrents which rise slowly with time and depend sub-linearly on light intensity, both hallmarks of trap limited processes. Because the photoresponse depends relatively weakly on bandgap, the ratio of photo- to dark conductivity is largest for the sulphides because of their lower dark conductivities. As such, MoS₂ and WS₂ may be best suited to photo-detection applications. However, due to their lower bandgap and superior conductivity, WSe₂ and WTe₂ might prove more effective in other applications, for example in photovoltaic cells.