Sea urchin-like TiO2 microspheres as scattering layer of nanosized TiO2 film-based dye-sensitized solar cell with enhanced conversion efficiency

• Anatase TiO2 microspheres with hierarchical nanoribbon structure are prepared.
• Bilayer solar cell using the microspheres as overlayer of nano-TiO2 film is reported.
• Bilayer cell exhibits better performance than the single nano-TiO2 film-based one.
• TiO2 microspheres overlayer can enhance both light harvesting and dye-loading.
• Bilayer cell exhibits decreased charge recombination and an improved voltage.

Sea urchin-like TiO2 microspheres are synthesized through a facile one-step solvothermal process by using titanium tetrabutoxide (TBOT) as titanium source. The obtained TiO2 microspheres with ∼3 μm diameter display anatase phase and hierarchical structures composed of TiO2 nanoribbons containing secondary nanoparticles with an average particle size of ∼15 nm. By using as photoanode material, the anatase TiO2 microspheres film-based dye-sensitized solar cells (DSSCs) show higher short-circuit current but slightly lower conversion efficiency than the TiO2 nanoparticles (P25) film-based one; while the bilayer film-based solar cell by using the TiO2 microspheres as overlayer of the P25 film exhibits significantly improved photovoltaic performance with an efficiency up to 7.14%, improved by 26.6% as compared to the P25 film-based one (5.64%). The anatase TiO2 microspheres as overlayer can not only enhance the light harvesting capability due to their scattering effect of the sea urchin-like hierarchical structures, but also contribute to the larger dye-loading amount, which lead to a decrease in the charge transfer resistance, charge recombination and dark current, and then resulting in the improved photovoltage and photovoltaic performance. The simple fabrication method of the bilayer solar cell, which contains a photoanode composed of P25 film as underlayer and sea urchin-like TiO2 hierarchical microspheres as overlayer, demonstrates a strategy for the development of the low cost and high efficiency solar cells through tuning the photoanode's component and structure.