Synthesis of nanobranched TiO2 nanotubes and their application to dye-sensitized solar cells

Nanobranched TiO2 nanotubes (TONTs) were synthesized by a sol–gel dipping method for the formation of seed layer, followed by a solution-phase deposition process. The different concentrations of seed solution influence the density of nanobranches on the top surface of TONT, achieving complete surface coverage of nanobranches in 10 mM TiCl4 seed solution relative to 5 mM TiCl4 seed solution. With a control sample of bare TONT, the nanobranched TONTs were explored as a photoanode for dye-sensitized solar cells (DSSCs). In the 5 mM TiCl4 seed solution, the nanotree-shaped branches were sporadically formed on the top surface of TONT, with little effect on the photocurrent-voltage (J–V) properties, while in the 10 mM TiCl4 seed solution, Jsc and fill factor increased, which may have been on account of the increased surface area and light scattering effect from rutile nanobranches, whereas the fill factor may be also increased by the electron transport property, leading to the degraded charge recombination. Accordingly, the nanobranched TONT showed 33% improved efficiency compared to bare TONT.