Control of crystal growth of ZnO nanowhiskers in aqueous solution and synthesis of transparent nanoarrays

Transparent and porous ZnO nanowhisker arrays were prepared in 0.025 M zinc nitrate-hexamethylenetetramine aqueous solutions with the addition of polyethylenimine (PEI) at a low temperature. The effect of free zinc ion concentration was controlled by changing the immersing temperatures at which the pre-treated FTO substrates were got into the mixing solution such as 25 °C, 75 °C and 85 °C. The free Zn ion concentration is a main factor for control of the transmittance. It was found that high Zn ion concentrations resulted in relative thick white and low transparent ZnO film, while the low concentrations gave high transparenency in the nanoarray. A transmittance of about 85% for porous ZnO films with thickness of 800 nm in the visible range was achieved.