Sponge-like Porous ZnO Photoanodes for Highly Efficient dye-sensitized Solar Cells

We propose a 3D branched ZnO nanostructure for the fabrication of highly efficient dye-sensitized solar cell photoanodes. A coral-shaped structured Zn layer was deposited by radio frequency magnetron sputtering at room temperature onto fluorine-doped tin oxide/glass sheets and then thermally oxidized in ambient atmosphere, obtaining a high-density branched ZnO film. The porous structure provides a large surface area, and, as a consequence, a high number of adsorption sites, and the size and spacing of the nanostructures (on the order of the exciton diffusion length) are optimal for good electron collection efficiency. The proposed synthesis technique is simple and scalable and the reproducibility of the growth results was tested. The crystalline phase of the film was investigated, evidencing the complete oxidation and the formation of a pure wurtzite crystalline structure. ZnO-based solar harvesters were fabricated in a microfluidic architecture, using conventional sensitizer and electrolyte. The dependence of the cell efficiency on dye incubation time and film thickness was studied with I-V electrical characterization and electrochemical impedance spectroscopy. The obtained conversion efficiency values, with a maximum value of 4.83%, confirm the highly promising properties of this material for the implementation in dye-sensitized solar cell photoanodes.