Pore-size effect on photovoltaic performance of dye-sensitized solar cells composed of mesoporous anatase-titania

The effect of the pore size of mesoporous anatase-TiO2 on the photovoltaic performance of dye-sensitized solar cells (DSSCs) is investigated. The mesoporous TiO2 particles are synthesized by two different methods using a soft template of tri-block copolymer and a hard template of mesoporous ZnO/Zn(OH)2-composite. These methods produce the same high surface area (SBET ∼ 210 m2 g−1) but different pore sizes of 6.8 and 3.0 nm, respectively. With the mesoporous TiO2 having larger pores, the photo-conversion efficiency (η) is increased significantly to 6.71%, compared with 5.62% that is typically achieved using P25 TiO2 nanopowders. By comparison, only half the performance (3.05%) has been observed with mesoporous TiO2 that has small pores. Mesoporous TiO2 with suitable pore sizes (∼6.8 nm) makes the most of its high surface area and thereby allows a high uptake of dye to enhance the current density. In contrast, the low efficiency of mesoporous TiO2 with small pores is attributed to the low uptake of dye due to the smaller pore size (∼3.0 nm), which blocks the diffusion and adsorption of dye molecules through the pores.

Research highlights▶ Mesoporous TiO2 photoelectrodes are synthesized using two different templates. ▶ They are engineered to have similar surface area but different pore sizes. ▶ The pore size turns out to be greatly related to the efficiency of the DSC. ▶ The small pore size induces low uptake of dye, producing much lower efficiency. ▶ The proper pore size enhances the current density, significantly increasing the efficiency.