A novel synthesis of the bottom-straight and top-bent dual TiO2 nanowires for dye-sensitized solar cells

The bottom-straight and top-bent dual anatase TiO 2 nanowires directly on flurine-doped tin oxide (FTO) glass substrate are successfully synthesized for the first time via a two-step solvothermal reaction, which obtains single anatase TiO 2 nanowires with the diameter of 250–450 nm and the length of ∼49 μm in the first growth step, and the slender TiO 2 nanowires with the diameter of 40–80 nm intertwining larger nanowires to form dual nanowires network in the secondary growth step. Dye-sensitized solar cell (DSSC) based on dual TiO 2 nanowires exhibits the power conversion efficiency of 5.30%, which is much higher than those of DSSCs based on the pristine single TiO 2 nanwires (2.36%) due to the twining network like dual nanowires structure maintaining excellent electron transport and simultaneously enhancing the specific surface area and light scattering ability. Moreover, by TiO 2 sol treatment, the performance of dual TiO 2 nanowires based DSSC can be further enhanced, reaching an impressive power conversion efficiency (PCE) of 7.65%.