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

Abstract

Size-tunable mesoporous spherical TiO₂ (MS TiO₂) with a surface area of ∼110 m² 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 ∼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.