Designed synthesis and stacking architecture of solid and mesoporous TiO₂ nanoparticles for enhancing the light-harvesting efficiency of dye-sensitized solar cells

We fabricated solid and mesoporous TiO₂ nanoparticles (NPs) with relatively large primary sizes of approximately 200 nm via inorganic templates for aero-sol-gel and subsequent aqueous-washing processes. The amount of dye molecules adsorbed by the internal pores in the mesoporous TiO₂ NPs was increased by creating the nanopores within the solid TiO₂ NPs. Simultaneously, the light-scattering effect of the mesoporous TiO₂ NPs fabricated by this approach was secured by maintaining their spherical shape and relatively large average size. By precisely accumulating the fabricated solid or mesoporous 200 nm diameter TiO₂ NPs on top of a conventional 25 nm diameter TiO₂ NP-based underlayer, we could systematically examine the effect of the solid and mesoporous TiO₂ NPs on the photovoltaic performance of dye-sensitized solar cells (DSSCs). Consequently, the stacking architecture of the mesoporous TiO₂ NP-based overlayer, which functioned as both a light-scattering and dye-supporting medium, on top of a conventional solid TiO₂ NP-based underlayer in a DSSC photoelectrode (i.e., double-layer structures) was found to be very promising for significantly improving the photovoltaic properties of conventional solid TiO₂ NP single-layer-based DSSCs.