Size-tunable mesoporous spherical TiO2 as a scattering overlayer in high-performance dye-sensitized solar cells

Size-tunable mesoporous spherical TiO2 (MS TiO2) with a surface area of similar to 110 m(2) g(-1) have been prepared through combination of dilute mixing-driven hydrolysis of titanium(iv) tetraethoxide and solvothermal treatment. The hierarchically structured MS TiO2 are characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and nitrogen sorption analysis. Using three different MS TiO2 (587, 757, and 1554 nm in diameter) as a scattering overlayer on a transparent nanocrystalline TiO2 film, bi-layered dye-sensitized solar cells (DSCs) have been fabricated. Since the MS TiO2 particles are comprised of similar to 10 nm nanocrystallites that cluster together to form large secondary spheres, they can function as light scatterers without sacrificing the surface area for dye-uptake. As a result, the present MS TiO2-based cells perform a noticeable improvement in the overall efficiency: maximum 9.37% versus 6.80% for the reference cell made of a TiO2 nanocrystalline film. This extraordinary result is attributed to the dual effects of enhanced dye loading and light scattering.