Electronic structure and transport properties of bilayer graphene adsorbed by LiF2 super-halogen clusters and Li3O super-alkali clusters

The lack of a band gap limits the practical applications of graphene in electronic devices. Using first-principles calculations with a van der Waals correction, we investigated the electronic structure and transport properties of bilayer graphene (BLG) adsorbed by super-halogen clusters and super-alkali clusters. BLG sandwiched between a pair of LiF2 super-halogen and Li3O super-alkali molecules enables the energy band to open a gap of about 0.36 eV and 0.26 eV near the Fermi energy, making the system exhibit semiconducting properties, which are attributable to the strong dipole electric field between the LiF2 super-halogen and Li3O super-alkali molecules. We also found that Li3O and the adjacent layer of graphene provide an energy band at the bottom of the conduction band and that LiF2 and the adjacent layer of graphene provide an energy band at the top of the valence band. The spatial separation of the electrons and holes is highly suitable for obtaining highly efficient photoelectric conversion in photovoltaic cells. We used the density functional theory and the non-equilibrium Green's function to determine the transport properties of the pristine BLG and the molecule-adsorbing BLG. A negative differential resistance effect occurred and an asymmetrical IV curve was observed under positive and negative bias, which is due to the inherent electric field effect between the graphene layers in the molecule-adsorbed BLG.