Reduced Graphene Oxide Wrapped Mesoporous Hierarchical TiO2-CdS as a Photoanode for High-Performance Dye-Sensitized Solar Cells

We developed a facile strategy for the fabrication of TiO2/CdS/RGO (RGO = reduced graphene oxide) composites as photoanodes for dye-sensitized solar cells (DSSCs) by growing CdS on the surface of mesoporous hierarchical TiO2 and then wrapping the TiO2/CdS with graphene oxide nanosheets. The TiO2/CdS/RGO nanostructures display an enhanced light-harvesting efficiency with a redshift from the ultraviolet to visible region and show an improved dye-adsorption capacity owing to the large surface area and mesoporous structures. Furthermore, the recombination of photoinduced electron-hole pairs can be greatly suppressed owing to the matched band-gap structures of TiO2 and CdS. The RGO nanosheets have excellent electric conductivity and provide unhindered pathways for accelerated electron transfer. Electrochemical impedance spectroscopy measurements demonstrate the enhanced charge-transfer kinetics and prolonged lifetime of the photogenerated electrons for the TiO2/CdS/RGO nanostructures. DSSCs based on TiO2/CdS/RGO photoanodes exhibit a greatly enhanced short-circuit current density of 13.27 mAcm(-2) and an improved photoelectric conversion efficiency of up to 6.5%, and these values are 31 and 44% higher than those of DSSCs based on a pristine TiO2 photoanode. The remarkable photoelectric performance of the DSSCs based on mesoporous hierarchical TiO2/CdS/RGO hybrid photoanode can be attributed to synergistic effects between the TiO2/CdS heterojunction and the graphene nanosheets.