Tuning the optoelectronic properties of monolayer MoS2 (1L-MoS2) is highly desired for optoelectronic applications. Gaining profound insights into the fundamental mechanisms that govern optoelectronic properties is of utmost significance. Here, we demonstrate that the photoluminescence (PL) of 1L-MoS2 can be modulated by photochemically functionalized graphene (F-G), which is covalently modified by oligophenyl groups. More importantly, the layer stacking sequence of F-G and 1L-MoS2 brings different interface structures, resulting in a significant difference in the PL enhancement. MoS2 supported by F-G (F-G/MoS2) has a 5-fold PL enhancement, while it only shows a 1.8-fold PL enhancement if stacked underneath F-G (MoS2/F-G). Accordingly, the results indicate that the oligophenyl groups in F-G/MoS2 not only have a p-doping effect on MoS2 but also largely prevent electron donation from the graphene basal plane with an enlarged interlayer distance of 8 nm. Consequently, the PL enhancement is lost with the thermal defunctionalization of F-G. Thus, we conclude that the functional groups can be considered as separate molecular components with the vertical arrangement in the functionalized heterostructure system. The photoactive graphene acts as a template for perpendicular molecular alignment in the heterointerface construction. The F-G/MoS2 heterostructures bring new perspectives to the design and investigation of optoelectronic devices.
