ZnS/ZnO Heteronanostructure as Photoanode to Enhance the Conversion Efficiency of Dye-Sensitized Solar Cells

ZnS/ZnO heteronanostructures were prepared to serve as the photoanode of the dye-sensitized solar cells. Two nanostructures, namely, ZnS/ZnO coaxial nanowires and ZnS/ZnO hierarchical nanowires (ZnS nanoparticles on ZnO nanowires), were successfully synthesized by chemical bath deposition and chemical etching processes, respectively. For both of the nanostructures, the ZnS coating can enhance photocurrent and conversion efficiency compared with the bare ZnO nanowires. We propose that ZnS layers in the two nanostructures take effect in different ways in that the ZnS compact layer in the coaxial structure retards the back transfer of electrons to the dye and electrolyte, while the coarse surface of ZnS nanoparticles in the hierarchical nanowires significantly enhances the adsorption of dye molecules. Hence, the ideal photoanode structure for high power-conversion efficiency should have both the compact shell layer and the high surface roughness.