Improvements to the hierarchically structured ZnO nanosphere based dye-sensitized solar cells

Hierarchically structured ZnO nanospheres are synthesized by a wet-chemical method and ZnO sphere-consisting films are applied to dye-sensitized solar cells (DSSCs). It is found that the overall light-to-electricity conversion efficiency (η) is significantly enhanced from 0.474% to 1.03% due to light scattering compared with the ZnO nanoparticle-based DSSC. However, the fill factor (FF) and open-circuit voltage (Voc) decrease obviously. After annealing the films in an oxygen environment and placing a ZnO blocking layer on the fluorine-doped SnO2 (FTO) conducting substrate, the FF and Voc are greatly improved and η increases from 1.03% to 1.59% and 2.25%, respectively. According to the results of x-ray diffraction and photoluminescence, the significant improvements in the cell performances might be due to the suppression of the recombination and the decrease in the resistances existing in the cell.