Interlayer charge transfer in graphene-2D polyimide heterostructures

The vertical integration of multiple two-dimensional (2D) materials in heterostructures, held together by van der Waals forces, has opened unprecedented possibilities for modifying the (opto-)electronic properties of nanodevices. This not only allows for the exploration of new physical phenomena but also greatly broadens the application horizon of existing monolayer devices. Graphene, with its remarkable opto-electronic properties, is an ideal candidate for such applications. The other potential candidates are 2D polymers, crystalline polymeric materials with customizable structures and electronic properties, as they can be synthesized in all mathematically possible Bravais lattices. In this study, we investigated the optoelectronic properties of a heterostructure created by pristine graphene and a rectangular 2D polyimide (2DPI) film. This imprints a new superlattice on graphene in conjunction with a direct influence on its electronic properties. Theoretical and experimental analyses reveal that interlayer charge exchange between the 2D polymer and graphene induces hole doping in the graphene layer. We have also observed that the properties of the heterostructure are dependent on the substrate used in experiments, likely due to the porous character of the 2DPI allowing direct interaction of graphene with the support. Furthermore, we demonstrate a direct correlation between the thickness of the 2DPI layer and the extent of hole doping in graphene. These findings highlight the unique ability to tailor functionalities in 2D polymers-based heterostructures, opening avenues for the development of optoelectronic devices with precisely engineered properties and stimulating further exploration of the diverse phenomena accessible through tailored designs of the 2D polymers.