(471b) Mesoporous TiO2 Beads From a Facile One-Step Template-Less, Surfactant-Free Hydrothermal Process and Derived TiO2 Bead/Xerogel Composites for High Efficiency Dye-Sensitized Solar Cells

A facile one-step template-less, surfactant-free hydrothermal process is developed to produce sub-micron sized mesoporous TiO₂ beads of high specific surface areas. No templates or structure directing surfactants are involved in the process. In addition, the beads are produced in one-step, unlike the two-step process (sol-gel followed by solvothermal) commonly adopted in the literature. The as-prepared TiO₂ beads are crystalline of the anatase phase, with a high specific surface area of 150 m²/g and an average pore size of 7.8 nm, and sub-micron in size, 500-800 nm. TiO₂ xerogels are incorporated into the TiO₂ bead layer to form a TiO₂ bead/xerogel composite to serve as the photoanode of dye-sensitized solar cells. A high power conversion efficiency of 8.41% is achieved from the TiO₂ bead/xerogel composite photoanode, representing a 33% improvement over the efficiency of 6.32 % achieved with a P-25 TiO₂ photoanode under the same characterization conditions. The success of the present composite TiO₂ nanostructure can be attributed to the excellent structure connectivity within the bead and xerogel domains for easy electron transport, the high specific surface areas of both the beads and xerogels for providing abundant dye adsorption for generation of photon-induced electrons, and the submicron size of the beads for much improved light harvesting efficiency resulting from the intense light scattering.