Effect of substrate pre-treatment on controllable synthesis of hexagonal WO3 nanorod arrays and their electrochromic properties

Hexagonal WO3 nanostructures with controlled sizes and alignment ordering have been successfully realized on fluorine doped tin oxide (FTO) substrates with different pre-treatment methods by a hydrothermal approach. The effects of the pre-treatment conditions, such as pre-coating a layer of WO3 nanoparticles, the annealing temperature and time and the colloid concentration, on the orientation and morphology of the WO3 nanorods were systematically investigated by scanning electron microscopy and X-ray diffraction. The WO3 nanorod arrays (WNRs) vertical to the FTO substrate and spindle-like nanorod bundles parallel to the FTO substrate can be selectively prepared depending on the crystallinity and the density of the WO3 seeds pre-coated on the FTO substrates. Moreover, the influence of the as-prepared WO3 morphology on its electrochromic (EC) property was also discussed.