Synthesis of hierarchical nanoparticles-based ZnO spheres for their application as the light blocking layers in dye-sensitized solar cells

Three-dimensional nanoparticles-based ZnO hierarchical spheres (ZnO-HS) with strong light harvesting and dye loading abilities have been fabricated by a simple hydrothermal method in this paper. These ZnO-HS were designed as the overlayer for light blocking and applied to the dye-sensitized solar cells (DSSCs) based on bare ZnO nanoparticles (ZnO-NP) or TiO₂ nanoparticles (TiO₂-NP). The results show that the values of the short-circuit current density (J _sc) and the power conversion efficiency (η) have been heightened up to 12.6 mA cm⁻² and 3.40 % for the ZnO-NP/ZnO-HS double-layered DSSC, far higher than the bare ZnO-NP DSSC. However, another DSSC assembled by the TiO₂-NP/ZnO-HS double-layered film displays an adverse result for the decreasing of J _sc and η even though the ZnO-HS light blocking layer has been established on the TiO₂-NP film. According to the electrochemical impedance data compared between the ZnO-NP/ZnO-HS double-layered and TiO₂-NP/ZnO-HS double-layered DSSC, it is found that the former possesses less possibility for the occurrence of charge recombination and electronic loss, which is responsible for its better photovoltaic response.