Graphene-Organic Two-Dimensional Charge-Transfer Complexes: Intermolecular Electronic Transitions and Broadband Near-Infrared Photoresponse

Charge-transfer (CT) complexes with unique intermolecular electronic transitions have attracted broad interest and hold great potential in optoelectronic applications. Here, we report a new family of two-dimensional graphene-organic molecule CT complexes. Density functional theory (DFT) calculation has revealed low-energy CT bands in the near-infrared (NIR) region up to 2000 nm for graphene-TCNQ (tetracyanoquinodimethane), graphene-F(4)TCNQ (2,3,5,6-Tetrafluoro-tetracyanoquinodimethane) and graphene-TCOQ (tetrachloro-o-benzoquinone) complexes. Raman and electrical measurements have confirmed a partial charge transfer between graphene and the molecules at the ground state. CT excitations have been calculated by DFT and verified by optoelectronic measurements. The graphene organic CT complexes have shown a broadband photoresponse from the visible to NIR range, attributed to the intermolecular electronic transitions. Further, the photoresponsivity (up to 10(3) A/W) suggests a high photoelectrical gain arising from the photogating effect at the graphene/molecule interface. At last, the photoresponse property of the graphene-organic CT complexes can be tuned by electrical gating of graphene.