Fabrication of mesoporous TiO₂ submicro/nanospheres with high specific surface and application in dye-sensitized solar cells

Hierarchical mesoporous TiO₂ (HM-TiO₂) submicro/nanostructured spheres are prepared by water heating reflux of hydrolyzed TiO₂ precursors of organic titanium. These submicrometer-sized spheres with a diameter of ~300 nm are constructed with interconnected 5 nm TiO₂ nanocrystallites, which possesses a high surface area of 193 m²/g, while the direct calcined sample only obtains 9.07 m²/g. UV–Vis spectrum shows that the HM-TiO₂ sphere has excellent dye absorption of 2.27 mol/cm² which is 6.67 times more than that of the direct calcined sample. When used as the photoanode in dye-sensitized solar cells (DSSCs), such submicro/nano-structured TiO₂ effectively enhanced light harvesting and increase the photocurrent of the DSSCs. Meanwhile, their good crystallinity and better interparticle connections caused by well-packed anatase TiO₂ nanocrystallites result in the effective charge transport. An energy conversion efficiency of 6.53 % was demonstrated based on the pure HM-TiO₂ photoanode, indicating 4.26 times improvement when compared with the cell derived from the directly calcined samples (1.53 %). Meanwhile, the optimized DSSCs that incorporate HM-TiO₂ into the top scattering layers exhibited excellent light-to-electricity conversion efficiency of 8.12 %. This is mainly attributed to the fact that the high surface area and high dye adsorption of HM-TiO₂ lead to more electron production and increase the short-circuit density.