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A very cheap solvent, ethanol, was successfully applied to control ZnO crystal growth for fabricating a series of ZnO composite nanostructures. During the experimental process, a two-step chemical route was adopted. In step-one, ZnO nanowire arrays were grown on fluorine-doped tin oxide coated glass substrate. In step-two, the step-one prepared samples were used as substrates for composite nanostructure deposition. The morphologies of the obtained products were characterized by field emission scanning electron microscopy. The results indicate that the morphologies of the final products can be effectively controlled by changing the water/ethanol ratios in the chemical solution. The obtained ZnO composite nanostructures with various morphologies were successfully employed in dye-sensitized solar cells. The light-to-electricity conversion results show that the composite nanostructures consisting of nanowires and pseudospherical nanostructures enable 80% improvement in solar energy conversion efficiency as compared with the nanowire arrays. These results indicate that the synthesized ZnO composite nanostructures are more suitable for application as photoelectrodes in solar cells.

CdO nanowires and nanotubes have been synthesized by the two-step temperature-controlled thermal evaporation process without any catalyst. The results demonstrate that CdO nanowires synthesized by vapor–solid mechanism grow along the [1 1 1] direction and their surface is surrounded by polyhedron-shaped CdO nanocrystals. The formation of nanocrystals should be attributed to the existence of dangling bonds in the sidewall of nanowires. We also successfully synthesized CdO nanotubes and deduced their formation mechanism. The difference of growth orientation for nanotubes and nanowires should be most likely linked to processes of nucleation and growth. Furthermore, energy-dispersive X-ray spectrum and X-ray diffraction analysis also testify that the synthesized nanowires and nanotubes have face-centered cubic CdO structures and possess good crystallinity.