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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.

Stability and magnetism of MnO3 superhalogen clusters embedded in bilayer graphene are investigated on the basis of first-principles calculations. MnO3-doped bilayer structures exhibit negative formation energies; by comparison, MnO3 embedded in monolayer graphene shows higher negative formation energy. Compared to MnO3-doped monolayer graphene MnO3-doped bilayer structures have higher structural stability due to higher binding energies. The charge from the lower graphene layer by MnO3 clusters then transfers to the upper layer graphene. The significant p-d hybridization between C and O atoms in graphene and Mn atoms leads to the exchange interaction causing the spin polarization of bilayer graphene. The MnO3 doped structures exhibit a half-metal nature with potential applications for spin field effect transistors (spin-FETs).

Hybrid photovoltaic cells take the advantages of silicon in charge carrier separation and transport and organic dyes in strong complementary light absorption. Photovoltaic responses from a set of hybrid solar cells based on amorphous silicon and phthalocyanine dyes of double- or triple-layer heterojunction structures were investigated, which were found to have thickness dependence with the organic active layers. It was found that the photocurrent contributions from organic layers are limited, although they are strong light absorbers. The main photocurrent contributions are from the silicon counterpart.