Hierarchically structured microspheres for high-efficiency rutile TiO ₂-based dye-sensitized solar cells

Peachlike rutile TiO₂ microsphere films were successfully produced on transparent conducting fluorine-doped tin oxide substrate via a facile, one-pot chemical bath route at low temperature (T = 80-85 C) by introducing polyethylene glycol (PEG) as steric dispersant. The formation of TiO₂ microspheres composed of nanoneedles was attributed to the acidic medium for the growth of 1D needle-shaped building blocks where the steric interaction of PEG reduced the aggregation of TiO₂ nanoneedles and the Ostwald ripening process. Dye-sensitized solar cells (DSSCs) assembled by employing these complex rutile TiO₂ microspheres as photoanodes exhibited a light-to-electricity conversion efficiency of 2.55%. It was further improved to a considerably high efficiency of 5.25% upon a series of post-treatments (i.e., calcination, TiCl₄ treatment, and O ₂ plasma exposure) as a direct consequence of the well-crystallized TiO₂ for fast electron transport, the enhanced capacity of dye loading, the effective light scattering, and trapping from microstructures.