Optimizing the prepared condition of TiO2 1D/3D network structure films to enhance the efficiency of dye-sensitized solar cells

Abstract

A novel structure of TiO₂ films has been successfully prepared on a fluorine-doped tin oxide (FTO) glass substrate through a feasible two-step hydrothermal method. In the first-step hydrothermal growth results in one-dimensional (1D) rutile TiO₂ nanorod arrays capped by 3 dimensional (3D) rutile TiO₂ nanorods, and in the second-step hydrothermal etching in hydrochloric acid solution leads to the selective etching of 3D TiO₂ nanorods to form 3D nanotubes at first, and then the tip wall of the nanotubes divide into secondary nanowires with reduced diameters. The resultant bi-layer TiO₂ network structure films were used as photoanodes in dye-sensitized solar cells (DSSCs). The 3D rutile network structure provides a large surface area for dye-loading and the oriented nanorod arrays at the bottom layer enable a direct pathway for electron transport. The influence of etching time toward the photovoltaic performance of the DSSCs fabricated from TiO₂ network structure films has been comprehensively studied. It was found that the amount and the length of the secondary nanowires reached a maximum when the etching time was 14 h, which resulted in the largest surface area and best dye-loading ability of the TiO₂ network structure films, producing an overwhelming power conversion efficiency (PCE) of 5.71%. In addition, TiCl₄ post-treatment was employed to further improve the PCE. Through optimizing the amount of the titanium precursor and the time of TiCl₄ treatment, the DSSCs assembled with a TiO₂ 1D/3D network structure photoanode presented a markedly enhanced efficiency of 7.68%, when the TiO₂ films were synthesized with 0.9 ml tetrabutyl titanate followed by 12 h etching and treated with TiCl₄ for 48 h.