Highly ordered hierarchical TiO2 nanotube arrays for flexible fiber-type dye-sensitized solar cells

Highly ordered hierarchical TiO2 nanotube (HTNT) arrays are obtained with a facile and low-cost approach, which can be applied in flexible fiber-type dye-sensitized solar cells (DSSCs). To achieve the HTNT arrays, smooth TiO2 nanotube (STNT) arrays are fabricated by a two-step anodization process followed by hydrothermal treatment in the presence of the aqueous solution of NH4F. Both STNT and HTNT arrays can serve as photoanodes in the flexible fiber-type DSSCs. We demonstrate that the conversion efficiency of the HTNT array-based flexible fiber-type DSSC (8.6%), which has increased by more than 30% compared with that of the STNT array-based flexible fiber-type DSSC. Moreover, the conversion efficiency is highly stable, even when the flexible fiber-type DSSC is subjected to extreme mechanical deformation, such as 180 degrees bending. This promising conversion efficiency may originate from the significant dye loading capability of the photoanode, which has an enormous surface area benefited from the hierarchical nanostructures.