Effect of post-annealing hydrothermal-grown ZnO nanorods on the electrical parameters of dye-sensitized solar cells

We annealed hydrothermal-grown ZnO nanorods in oxygen and reducing environment (foaming gas) at 450°C and investigated its effect on the performance of dye-sensitized solar cells. The changes in morphology and surface damage due to annealing were not spotted. From photoluminescence and X-ray diffraction spectra, we observed that visible emission related to defect states, especially yellow-green emission peak at ~580 nm, was suppressed and crystallinity was also improved by both oxygen and foaming gas annealing. Despite these improvements, we found only marginal increase in current density because the removal of hydroxyl groups due to annealing brings a negative impact on the dye loading. Nevertheless, the open-circuit voltage and fill factor increase upon annealing due to the inhibition of recombination through defect states in nanorods.