Transparent ultrathin all-two-dimensional lateral Gr:WS2:Gr photodetector arrays on flexible substrates and their strain induced failure mechanisms

Abstract

Herein, we detail developments in the scalable fabrication of all-two-dimensional (2D) flexible and transparent photodetectors. These devices were fabricated from chemical vapour deposition derived graphene and tungsten disulphide on poly(ethylene naphthalate) (PEN), a material commonly used as a substrate in flexible electronics. Alternative patterning approaches that are necessitated by the more thermally and chemically sensitive polymer substrates are explored, resulting in several modifications to conventional, silicon-substrate device fabrication approaches. In particular, the relatively new lift-off patterning approach for 2D materials is applied as an alternative to plasma etching due to the deleterious effect of plasma on the PEN substrates. This enabled the observation of a strain-modulated enhancement of photocurrent of up to one order of magnitude, demonstrating the utility of strain engineering to the field of 2D devices—provided it can be controllably applied. Further application of strain led in all cases to permanent failure and loss of photoconductivity, the details of which are explored using scanning electron microscopy. These results provide important details relevant to the fabrication of large-scale arrays of flexible and transparent 2D devices on polymer substrates.