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 (~ 30 μm) was nearly doubled in the cells with bimodal pore size distribution, compared with the previously reported optimal coating thickness (~ 15 μm) 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.

Research Highlights
► The I3− ion diffusion coefficient increased with the increasing mean size of nano-pores.
► Nano-pores and submicro-pores show synergism enhancement for ion diffusion.
► A higher ion diffusion property led to an increase in open circuit voltage.
► The optimal coating thickness was 30 μm for solar cell with TiO2 of bimodal-sized pores.