Mesoporous titania hollow spheres applied as scattering layers in quantum dots sensitized solar cells

Quantum dots sensitized nanocrystalline TiO ₂ solar cells (QDSSCs) have attracted great attention for its promising prospects. In order to enhance the effective light absorption path length in the photoanode, a scattering layer is often applied on the back of the transparent absorption layer. Compared with conventional scattering layer films composed of 20 nm and 300 nm TiO ₂ nanocrystalline, submicrometer-size mesoporous TiO ₂ hollow spheres are of great interest due to its lower fabrication temperature and hierarchical pore structures. Here we present a novel solvothermal method to prepare mesoporous anatase TiO ₂ hollow spheres via a hydrophilic template/non-polar solvent interface reaction with carbon sphere as templates, which is easy to control the grain and pore size as well as the shell thickness of the hollow spheres. The TiO ₂ hollow spheres in average size of 320-330 nm have been applied as the scattering layer materials in CdSe QDSSCs grown by successive ionic layer adsorption and reaction, and a power conversion efficiency of ca. 3.2% has been obtained. The efficiency is higher by 28% than that of the QDSSCs with the scattering layers composed of 20 nm and 300 nm TiO ₂ particles due to its much higher optical reflectance and longer electron lifetime resulted from its fast diffusion of the electrolyte and lower CdSe loading in the scattering layer. It is indicated that high QDs loading in the scattering layers can cause the downwards displacement of the TiO ₂ conduction band and lead to lower electron lifetime for the QDSSCs with alkali polysulfide as electrolyte, which was different from the conventional dye-sensitized solar cells.