Hollow hemispherical titanium dioxide aggregates fabricated by coaxial electrospray for dye-sensitized solar cell application

Abstract

Hollow hemispherical titanium dioxide (TiO2) aggregates (HHTAs) consisting of P25 TiO2 nanocrystallites were prepared by a coaxial electrospray method and applied to dye-sensitized solar cells (DSCs). Although the photoelectrode film constructed with HHTAs possesses an internal surface area lower than that of one with dispersed P25 TiO2 nanocrystallites and thus achieves less dye adsorption, it may generate effective light scattering, which would significantly extend the traveling distance of light within the photoelectrode film and therefore enhance the light-harvesting efficiency, leading to higher power-conversion efficiency (PCE). A bilayer photoelectrode film that consists of HHTAs as the top layer and P25 nanocrystallites as the base layer was also prepared for DSCs. This bilayer structure combines the merits of HHTAs for light scattering and nanocrystallites for sufficient surface area for dye adsorption and, accordingly, results in higher PCE than that of P25 nanocrystallites and HHTAs. Electrochemical impedance spectroscopy revealed that the photoexcited electrons transporting in the HHTA photoelectrode suffer less recombination than that in the P25 nanocrystallite photoelectrode, due mainly to lower specific surface area in the HHTA photoelectrode exposed to electrolyte, which contains oxidized species.