Large variations in both dark- and photoconductivity in nanosheet networks as nanomaterial is varied from MoS2 to WTe2. Issue 1 (18th November 2014) - Cunningham, Graeme
Abstract : We observe large variations in both dark- and photoconductivity of solution-processed networks of different transition metal chalcogenides. 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.