282764 Graphene Metal Oxide Nanoassemblies for Dye-Sensitized Solar Cells
Tremendous interest exists towards synthesizing nanoassemblies for dye-sensitized solar cells (DSSCs) using earth abundant and friendly materials with green synthetic approaches. Recently, two-dimensional graphene has initiated a rapid exploration of its potential in a broad range of fields including energy conversion and catalysis . Catalyst particles can be incorporated directly onto an individual graphene sheet, providing enhanced properties for DSSCs . Graphene is a good electron acceptor and can serve as charge trapping sites and reduce the electron-hole recombination rate to enhance the photoefficiency of titania.
In this research, uniform TiO2 nanowires were grown on the surface of graphene sheets using a sol-gel method in supercritical carbon dioxide (scCO2) to help exfoliate graphene while preventing agglomeration and controlling the particle size. Fe doped TiO2 on the graphene sheets were also prepared in both ethanol and scCO2 to extend its band gap to the visible region. TiO2 nanoparticles less than 5 nm (when ethanol was used as a solvent) and TiO2 nanowires less than 40 nm (when scCO2 was used as a solvent) were uniformly decorated on the graphene sheets. Both doped TiO2 nanoparticles and nanowires showed smaller crystal size, and higher visible absorption, surface area, and higher efficiency solar cells compared to similar materials without graphene. Theoretical band structures have been studied using the Vienna ab-initio Simulation Package (VASP) based on the Density Functional Theory (DFT). Band gap and adsorption energy values of structural TiO2 were calculated respectively in the bulk and on graphene by physisorption and chemisorption. Functionalized graphene sheets decrease significantly the band gap but increase the binding energy values, due to carboxylate adsorption sites, of structural TiO2 compounds which facilitate DSSC performance.
 Nasrin Farhangi, Yaocihuatl Medina-Gonzalez , Rajib Roy Chowdhury, and Paul A. Charpentier, Nanotechnology (2012), In Press.
 Nasrin Farhangi, Rajib Roy Chowdhury, Yaocihuatl Medina-Gonzalez,
Madhumita B. Ray and Paul A. Charpentier, Applied Catalysis B: Environmental
110 (2011) 25– 32.
 G. Kresse, D. Joubert, Phys. Rev. B 59 (1999) 1758