Reduced electron recombination of dye-sensitized solar cells based on TiO(2) spheres consisting of ultrathin nanosheets with [001] facet exposed

An anatase TiO(2) material with hierarchically structured spheres consisting of ultrathin nanosheets with 100% of the [001] facet exposed was employed to fabricate dye-sensitized solar cells (DSCs). Investigation of the electron transport and back reaction of the DSCs by electrochemical impedance spectroscopy showed that the spheres had a threefold lower electron recombination rate compared to the conventional TiO(2) nanoparticles. In contrast, the effective electron diffusion coefficient, D(n), was not sensitive to the variation of the TiO(2) morphology. The TiO(2) spheres showed the same D(n) as that of the nanoparticles. The influence of TiCl(4) post-treatment on the conduction band of the TiO(2) spheres and on the kinetics of electron transport and back reactions was also investigated. It was found that the TiCl(4) post-treatment caused a downward shift of the TiO(2) conduction band edge by 30 meV. Meanwhile, a fourfold increase of the effective electron lifetime of the DSC was also observed after TiCl(4) treatment. The synergistic effect of the variation of the TiO(2) conduction band and the electron recombination determined the open-circuit voltage of the DSC.