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

Abstract

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° 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.