Reconstruction of the (001) surface of TiO2nanosheets induced by the fluorine-surfactant removal process under UV-irradiation for dye-sensitized solar cells

Abstract

The champion dye-sensitized solar cells (DSSCs) based on TiO₂ nanoparticles nearly reach the limit of photo-current density using the black dye or zinc porphyrin dye as sensitizer. However, the way to make ordinary DSSCs more efficient as well as to understand the mechanism is still essential. Here we present an elegant UV irradiation treatment of TiO₂ nanosheets to enhance the performance of DSSCs based on the TiO₂ nanosheets via room temperature removal of inorganic surfactants and reconstruction of the (001) surface of TiO₂ nanosheets, killing two birds with one stone. UV irradiation was utilized to remove the fluorine-surfactant on the surface of anatase TiO₂ nanosheets with a high percentage of exposed {001} facets which were synthesized with the aid of hydrofluoric acid. The nanosheets treated with UV irradiation for 40 min had the advantage of improving the photoelectric conversion efficiency of DSSCs by 17.6%, compared to that without UV treatment when they were introduced into DSSCs as photoanode materials. The improved efficiency was ascribed to more dye adsorption. A theoretical calculation proposed that UV irradiation induced microfaceted steps on the TiO₂ surface by two domain (1 × 4) reconstruction after UV irradiating the (1 × 1) (001) surface. The microfaceted steps increase the active surface area of the TiO₂ nanosheets by increasing the exposure of titanium atoms and engendering active sites.