Synthesis of size controllable and thermally stable rice-like brookite titania and its application as a scattering layer for nano-sized titania film-based dye-sensitized solar cells

Abstract

Size controllable and thermally stable rice-like brookite TiO₂ particles with high phase purity were synthesized through a hydrothermal process. By varying the reaction conditions, the average diameter (brachyaxis) of the rice-like brookite TiO₂ particles can be tuned over a wide range from ca. 200 nm to 1200 nm. Moreover, the brookite phase can be maintained, even with calcination at a temperature up to 800 °C, and a brookite-to-anatase phase transition and then to rutile can be observed upon further enhancing the calcination temperature from 850 °C to 1000 °C. The obtained brookite TiO₂ submicrometer particles were used as a light scattering overlayer on a nano-sized TiO₂ (P25) film-based photoanode to fabricate bilayer TiO₂ film-based dye-sensitized solar cells (DSSCs). It is found that the brookite TiO₂ scattering layers can improve the performances of the P25 film-based solar cells to different extents by enhancing the light-harvesting capability, and the optimal diameter of the rice-like brookite TiO₂ particles as a scattering layer material is determined to be ∼600 nm, its corresponding solar cell gives an overall conversion efficiency up to 7.57%, with a ∼33% improvement in the efficiency as compared to that (5.70%) of the individual P25 film-based one under standard AM 1.5G 1 sun irradiation. The above results on the brookite TiO₂ particles represent a clear advance towards efficient light scattering materials for the nanosized TiO₂ film-based solar cells.