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This paper reports the effects of the aspect ratio of zinc oxide (ZnO) nanowires on the performance of ZnO-nanowirebased 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)/NH 3 . 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 µm). 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.

This paper reports a reproducible low-temperature solution-based process for the preparation of ZnO films of nanorod arrays and their application to dye-sensitized solar cells (DSSCs). A two-step approach was employed for the epitaxial growth of ZnO. We began with the preparation of a (002)-oriented ZnO seed layer by the electrochemical deposition method. After the treatment the substrate was soaked in an aqueous solution containing ZnCl2 and complex agents. A large-scale fabrication of ZnO nanorod arrays on transparent conductive oxides has been achieved after soaking at 95 degrees C for 1-48 h. The as-deposited ZnO film has a large surface area, therefore permitting a great amount of dye loading. The individually separated nanorod forms a linear nanoroad which should show more effective electron transportation than that in the film derived from ZnO powders. The DSSCs using these ZnO films as photoelectrodes show a conversion efficiency of about 0.6% at AM1.5.

A hydrotalcite-like film has been successfully deposited on an Al-bearing glass substrate based on an interface reaction between an Al layer and a zinc aqueous solution. The film selectively grew on the Al surface but not on the glass surface. The film on Al was composed of layered nanosheets of a hydrotalcite-like compound containing Al and Zn. Comparably, deposits on the plastic surface and precipitates in solution were wurzite-type ZnO with various morphologies depending upon the preparation conditions. At low supersaturation degrees, single crystals and superstructures of Zn-Al hydrotalcite were also obtained. This porous hydrotalcite film has a potential application as catalyst supports, environmental materials, or matrixes for hydrotalcite-based nanocomposite films. Using Al as a reaction interface makes it easy to coat porous hydrotalcites on a series of matrix materials varying in shapes and properties, which is important for achieving practical applications. In addition, the method developed should be widely applicable to other systems for the preparation of porous or oriented hydrotalcite-like thin films by an appropriate combination of divalent/trivalent solution-substrate systems.