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 degrees C for 12 h (regarded as nonsintering process) or 450 degrees 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 (tau) in the DSCs were measured under various light intensities. The DSCs with nonsintered TiO2 showed lower values of D and tau 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.