Ag nanoparticle-decorated 3D flower-like TiO2 hierarchical microstructures composed of ultrathin nanosheets and enhanced photoelectrical conversion properties in dye-sensitized solar cells

A double-layer TiO2 (Ag-TiO2-DL) photoanode with various loading amounts of Ag nanoparticles were designed with an underlayer composed of P25 TiO2 nanoparticles and an overlayer of 3D flower-like TiO2 hierarchical microstructures (TiO2-HS) and used to make a serious of dye-sensitized solar cells (DSSCs). The resulting nanostructures are characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, UV-visible spectroscopy, N-2 adsorption-desorption isotherms, and Raman spectroscopy. The influences of different loading amounts of Ag on the structure and performance of the DSSCs are investigated. Results indicate that the short current density (J(sc)), open-circuit voltage (V-oc) and charge lifetime of DSSCs containing Ag nanoparticles are significantly improved. Especially, the as-prepared Ag-TiO2-DL film at the nominal Ag loading of 0.8 wt% showed the highest photoelectric conversion efficiency of 8.98%, which exceeds that of pure TiO2-DL of 6.22%. Thus superior cell efficiency is mostly due to the increase of current density, attributed to that (i) a higher efficiency of light harvesting through the light scattering of overlayer; (ii) the efficient separation of photo-induced electrons and holes due to these novel hierarchical microstructures; (iii) the surface Plasmon resonance effect of Ag nanoparticles, which enhance the efficient charge separation and high carrier mobility. (C) 2015 Elsevier B.V. All rights reserved.