Anatase TiO ₂ beads having ultra-fast electron diffusion rates for use in low temperature flexible dye-sensitized solar cells

The first use of mesoporous TiO ₂ beads in plastic substrate flexible dye-sensitized solar cell (FDSC) is demonstrated. Pure anatase TiO ₂ beads with various sizes (250-750 nm) and characteristics are obtained using a modified and efficient two-step method. The concept of chemical sintering, eliminating the step of additive removal, is used to prepare bead-containing paste for room temperature fabrication of photoanode having good adhesion to the substrate. The obtained photoanodes are examined for their dye loadings and light absorbance properties. Various plastic substrate FDSCs having commercial P25- and bead-containing photoanodes are fabricated and evaluated. The resulting cells are evaluated for the J-V characteristics, electron diffusion time, electron lifetime, charge-collection efficiency, electron-injection efficiency and incident photon-to-electron conversion efficiency. The bead-only cells not only have better efficiencies, as high as ∼5%, but also exhibit ultra-fast electron diffusion rates, less than 1 ms (∼0.37 ms, 7.6 μm). The best efficiency and electron diffusion rates are respectively 15% higher and two-order of magnitude faster than the P25-only cell. The effects of the bead characteristics on the cell performance is presented and discussed.