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 wave-length region lambda = 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 x 10(-4) cm(2) 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.