Fig. 3. Optical images of MS (high)-left, SM (high)-middle, and HT (high)-right samples for (a) as prepared, and (b) after 12 hours of storage. The MS (high) sample showed precipitation of WS2 nanosheets after 12 hours due to the greyer solution dispersion in (b)-left, whereas the SM (high)-middle and HT (high)-right samples showed no visible precipitation given the darker colored dispersions persistent after storage. (c) The dark current Id–V measurement of inkjet printed graphene–WS2–graphene heterostructure device where the inset depicts the inkjet printed graphene–WS2–graphene heterostructure sample. (d) Dark current Id–V measurement on a log-scale which shows that Id ∼ 134.2 pA at 0 V which was the value used for the responsivity and detectivity calculations.
