Effect of mesoporous TiO₂ bead diameter in working electrodes on the efficiency of dye-sensitized solar cells.

Mesoporous TiO₂ beads with diameters of 320±50, 550±50, and 830±40 nm, comprising interconnected and densely packed TiO₂ nanocrystals, were used as working electrodes for dye-sensitized solar cells (DSCs). These electrodes possess high surface areas and superior light-scattering properties, which are ideal for DSC applications. Although the electrode prepared by using 320±50 nm beads demonstrated the highest dye loading and the electrode prepared by using 550±50 nm beads showed the best light-scattering properties in the wavelength region λ=400-800 nm, DSC devices with working electrodes composed of 830±40 nm beads achieved the highest power conversion efficiencies of 9.0 % after treatment with TiCl₄. A higher electron diffusion rate (4.35×10⁻⁴ cm²  s⁻¹) and an extended electron lifetime (58 ms) were observed in DSCs composed of the largest beads, 830±40 nm, attributable to a reduced amount of inter-bead barriers and a relatively small percentage of TiO₂ nanocrystals on the surface of the beads, compared to cells containing 550±50 and 320±50 nm beads.