Influence of pore structure on ion diffusion property in porous TiO₂ coating and photovoltaic performance of dye-sensitized solar cells

The ion diffusion in porous TiO₂ coating determines the limiting current density and the photovoltaic performance of a dye-sensitized solar cell. Nano-TiO₂ coatings with unimodal nano-size distribution and bimodal size distribution were deposited by vacuum cold spray to examine the effects of the pore structure on the ion diffusion property and cell performance. Results show that the I₃^- ion diffusion coefficient increased with the increase in the mean pore size. The bimodal size distribution of nanometer-sized and submicrometer-sized pores in the coating was found to have a synergistic enhancement effect on the ion diffusion. Better ion diffusion performance contributed to a higher open circuit voltage. The optimal coating thickness (~30μm) was nearly doubled in the cells with bimodal pore size distribution, compared with the previously reported optimal coating thickness (~15μm) in the cell with unimodal pore size distribution. The reason is attributed to the high ion diffusion coefficient which allows a high limiting current density.