Sugar apple-shaped TiO2 hierarchical spheres for highly efficient dye-sensitized solar cells

• The sugar apple-shaped TiO2 hierarchical spheres were prepared by a facile hydrothermal method.
• The TiO2 hierarchical spheres had a prominent light scattering effect.
• DSSCs based on TiO2 double-layer film had the maximum conversion efficiency.

The sugar apple-shaped TiO2 hierarchical spheres are prepared by a facile hydrothermal method using polyethylene glycol 600 as stabilized reagent, (NH4)2TiF6 and urea as starting materials at 180 °C. The characterizations show that the TiO2 hierarchical sphere has well-defined pyramid-shaped crystal facets. The as-prepared TiO2 hierarchical spheres are crystalline of the anatase phase, with a diameter of about 2–4 μm and a surface area of 36.846 m2 g−1. The optical investigation evidences that the sugar apple-shaped TiO2 hierarchical sphere film exhibits a prominent light scattering effect at a wavelength range of 600–800 nm due to the unique hierarchical morphology. Furthermore, the sugar apple-shaped TiO2 hierarchical spheres are deposited as the scattering layer to balance the dye adsorption and light scattering effect in DSSCs and a 7.20% solar energy conversion efficiency is demonstrated, indicating an improvement compared with the P25 cell (6.68%). Based on the optical and electrochemical investigations, the high conversion efficiency is mainly due to the effective suppression of the back reaction of the injected electron with the I3− in the electrolyte and excellent light scattering ability.

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