Optoelectronic Properties of MoS2/Graphene Heterostructures Prepared by Dry Transfer for Light-Induced Energy Applications

Optoelectronic properties of atomic thin van der Waals heterostructures (vdWHs) comprising transition metal dichalcogenides that harvest light energy are of paramount interest. In this work, the effects of underlying single- and bilayer graphene (Gr) layers on structural and physical properties of MoS2/Gr vertical heterostructures, i.e., (1-2L)MoS2/(1-2L)Gr, with additional interfaces including MoS2 folds/edges [MoS2(1L+1L))/Gr(1L)] and MoS2(1-2L)/Au, are investigated to unravel the excitonic properties. By employing correlative scanning probe microscopy combined with micro-spectroscopy, we observed multiple effects related to excitons (i.e., redshift of neutral excitons, ratio of charged excitons or trions to neutral exciton population, and long-tailed trions) and surface electronic properties (i.e., reduced work function suggesting electron transfer) in addition to significantly enhanced near-field Raman spectra, apparent n-p type current rectification behavior and increase in photogenerated carriers. All of these findings are attributed to interlayer electronic interactions while minimizing Fermi level pinning at the MoS2/Au interface, commonly observed in 2D semiconductor-3D metal junctions, which deepens our understanding of dissimilar 2D material junctions. Integrating MoS2 with an optimal number of graphene layers as a 'nanospacer' signifies substrate engineering that is versatile for key optoelectronic and photovoltaic applications.