Reconstruction of the (001) surface of TiO2 nanosheets induced by the fluorine-surfactant removal process under UV-irradiation for dye-sensitized solar cells

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 x 4) reconstruction after UV irradiating the (1 x 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.