Structural and chemical analysis of TiO2 nanotube surface for dye-sensitized solar cells

Abstract

One-dimensional TiO2 nanotube (TNT) arrays were fabricated on fluorine-doped tin oxide glass substrate as the photoanodes for dye-sensitized solar cells (DSCs) using one-step ZnO nanorods template method. The depth profile analysis using X-ray photoelectron spectroscopy and ion sputtering indicated that a small amount of Zn species was attached on the TNT surface. Relationship of the properties of the TNT surface with the Zn residue and the photovoltaic characteristics of DSCs were investigated. Residual Zn species on TNT improve the open circuit voltage of the DSCs. A maximum open circuit voltage of 0.876 V was achieved, which is close to the theoretical maximum of the TiO2-based DSCs. However, photocurrent density was decreased significantly for the high-Zn-amount sample. It was revealed that the surface Zn species were divalent oxides and the amount of surface hydroxyl group was increased in conjunction with the Zn amount. Slight increase of the dye amount was found for the high Zn amount sample. It was expected that decrease in injection probability of the photo-excited electrons into TNT was the dominant reason for the photocurrent decrease.