Effects of seeding temperature and growing time on the nanostructural characteristics of ZnO nanorods thin films prepared by chemical bath deposition

ZnO nanorods have been attracting much interest of researchers owing to their unique properties and extensive potential for various applications including light-emitting diode, dye-sensitized solar cells, and field-effect transistor. For being applied on those strategic applications, some basic nanostructural characteristics of ZnO nanorods such as crystallite size and the band gap energy are essential since they play important role in the device performance. In this study, the effect of seeding temperature and growing time on the nanostructure characteristics of ZnO nanorods were investigated. The seed solutions were initially prepared at the temperature of 0, 30, and 60°C for 1 hour by using zinc nitrate tetrahydrate and hexamethylenetetramine as precursors. The ZnO seed layers were subsequently deposited onto ITO glass substrates by spin coating technique before the chemical bath deposition (CBD) growth at temperature of 90°C for three different growth times (3, 4, and 5 hours). The synthesized ZnO nanorods were characterized by field-emission scanning electron microscopy, x-ray diffraction, and ultraviolet-visible spectrophotometry. The results showed that with the increase in seeding temperature from 0 to 60°C, the crystallite size decreased from 61.83 to 51.54 nm, while the band gap energy increased from 3.36 to 3.57 eV, respectively. On the other hand, with increase of growing time during CBD, the crystallite size was increased from 51.54 to 75.17 nm, and the band gap energy was consequently found to decrease from 3,57 to 3,46 eV. Considering the observed results above, the low seeding solution temperature and CBD growth time control are promising to optimize various applications performance required to have remarkably high crystallinity and low band gap energy.