Design of a TiO2 nanosheet/nanoparticle gradient film photoanode and its improved performance for dye-sensitized solar cells

Abstract

A TiO₂ film photoanode with gradient structure in nanosheet/nanoparticle concentration on the fluorine-doped tin oxide glass from substrate to surface was prepared by a screen printing method. The as-prepared dye-sensitized solar cell (DSSC) based on the gradient film electrode exhibited an enhanced photoelectric conversion efficiency of 6.48%, exceeding that of a pure nanoparticle-based DSSC with the same film thickness by a factor of 2.6. The enhanced photovoltaic performance of the gradient film-based DSSC was attributed to the superior light scattering ability of TiO₂ nanosheets within the gradient structure, which was beneficial to light harvesting. Furthermore, the TiO₂ nanosheets with exposed {001} facets facilitated the electron transport from dye molecules to the conduction band of TiO₂ and further to the conductive glass. Meanwhile, the high specific surface area of TiO₂ nanosheets helped the adsorption of dye molecules, and the TiO₂ nanoparticle underlayer ensured good electronic contact between the TiO₂ film and the fluorine-doped tin oxide glass substrate. The electrochemical impedance spectroscopy measurements further confirmed the electron transport differences between DSSCs based on nanosheet/nanoparticle gradient film electrodes and DSSCs based on nanosheet/nanoparticle homogeneous mixtures, pure TiO₂ nanoparticles and pure TiO₂ nanosheets with the same film thickness.