Hierarchical TiO2 submicron-sized spheres for enhanced power conversion efficiency in dye-sensitized solar cells

Hierarchical TiO 2 submicron-sized spheres (TiO 2 HSSs) with diameters of 400–600   nm were synthesized by a facile one-step solvothermal method in ethanol solvent. The HSSs composed of nanoparticles of ∼14   nm have a relatively large surface area of ∼35   m 2 /g. When applied as the scattering overlayer in dye-sensitized solar cells (DSCs), such TiO 2 HSSs effectively improved light harvesting and led to the increase of photocurrent in DSCs. Furthermore, bilayer-structured photoanode also provided fast electron transportation and long electron lifetime as confirmed by electrochemical impedance spectra. As a result, DSC based on P25 nanoparticle underlayer and HSS-2 overlayer exhibited the highest cell efficiency (6.23%) compared with ones with pure P25 (5.50%) or HSS-2 (2.00%) photoanodes.