Effect of surface etching on the efficiency of ZnO-based dye-sensitized solar cells.

In this study, we report on an insight into the influential factors of the conversion efficiency of ZnO-based dye-sensitized solar cells. With ZnO nanoflowers as the photoelectric anode and dye N719 as the sensitizer, we found with the addition of N719 that the surfaces of ZnO nanoflowers were slightly etched at the beginning and gradually destroyed with time. On the basis of these observations, a series of experiments were further carried out to distinguish the influence of dye-induced aggregation from that of dye-induced etching on the solar-to-electric conversion efficiency. SEM observation reveals that there were no obvious dye/Zn(2+) aggregations on any of the samples. XRD results indicate that there was no new phase formed during the dye-sensitizing process. I-V measurements reveal clearly that the efficiency of ZnO-based DSSCs was inversely proportional to the etching level of ZnO surfaces. We concluded that the dye-induced etching of the ZnO anode may be an assignable cause that results in the low efficiency of ZnO-based DSSCs. The etching of ZnO may lead to low surface absorption efficiency of the dye, low electron mobility, and a high surface recombination ratio of photocarriers. Therefore, we suggest that special attention should be paid to protecting the surface structure of the ZnO anode during the dye-sensitizing process.