Electron Transport and Recombination in Dye-Sensitized TiO₂ Solar Cells Fabricated without Sintering Process

Nanoporous TiO₂ electrodes were prepared from a colloidal suspension of TiO₂ nanoparticles with heating processes at 80 °C for 12 h (regarded as nonsintering process) or 450 °C for 30 min (as sintering process) in air, and dye-sensitized solar cells (DSCs) were prepared from them. Electron diffusion coefficients (D) and lifetime (τ) in the DSCs were measured under various light intensities. The DSCs with nonsintered TiO₂ showed lower values of D and τ than those in the sintered TiO₂ at the matched electron density. A plot of open-circuit voltage (V_oc) vs electron density of the DSCs showed that the nonsintered TiO₂ gave higher V_oc at the matched electron density under high light intensity and lower Voc under low light intensity. These results suggest that nonsintered TiO₂ has less density of shallow trap sites and sintering process will form the traps at the grain boundary during the growth of the necks between TiO₂ particles.