Nanosecond dynamics in few-layer and heterojunction transition metal dichalcogenides from liquid phase exfoliation

The lifetimes of photogenerated charge carriers must be long enough to guarantee high efficiency of light harvesting devices. Two-dimensional transition metal dichalcogenides (TMDs) are promising materials due to their intense light -matter interaction. Liquid phase exfoliation is a low-cost, versatile, scalable method able to produce polydisperse nanosheets in the form of inks. Here, we use nanosec-ond transient absorption spectroscopy to investigate the charge carrier dynamics in MoS2, WS2, and heterojunctions (HJs) of the two. We observe that the HJ stack-ing order does not affect the dynamics. We find that in thicker and larger flakes of the single material the carrier lifetime is significantly longer than even in HJs, due to different electronic contributions from nanosheet basal plane and edges. We conclude that there is no need for additional complexity in stacking two TMDs, and transport properties are enhanced in thicker and larger flakes. Our findings can be exploited for device fabrication.