Solution-derived ZnO nanowire array film as photoelectrode in dye-sensitized solar cells

This paper reports the effects of the aspect ratio of zinc oxide (ZnO) nanowires on the performance of ZnO-nanowire-based dye-sensitized solar cells (DSSCs). ZnO nanowire-structured photoanodes can improve the efficiency of the electron collection of DSSCs, but their performances significantly depend on the aspect ratio of component nanowires and their array structures. The aspect ratio of nanowires has been successfully regulated by controlling the supersaturation degree of solutions, that is, simply by changing the molar ratio of Zn(II)/NH3. A highly oriented, single crystalline, long ZnO nanowire with a fine aligning structure was obtained with an aspect ratio of about 100-120 (diameter: 120-150 nm, length: 14 mu m). The main crystalline phase measured by X-ray diffraction and Raman scattering was proven to be wurtzite-type ZnO, whereas the appearance of another phase was also detected. The films show a transmittance of about 60% in the visible light region and optical band gaps at around 3.2 eV. An overall conversion efficiency of about 1.7% was obtained, which is almost three times of that we reported previously. The present research points out a possible way to improve ZnO-based DSSCs by engineering a nanostructured electrode.