Morphology-tailored synthesis of vertically aligned 1D WO3 nano-structure films for highly enhanced electrochromic performance

Abstract

We have demonstrated that vertically aligned WO₃ nanostructure films can be fabricated on FTO-coated glass substrates using a template-free hydrothermal technique. Detailed mechanistic studies revealed that a variety of WO₃ nanostructures—including nano-bricks, 1D nanorods and nanowires, and 3D nanorod-flowers—could be obtained by tuning the composition of the precursor solution, where the urea content and solvent composition played important roles in controlling the shape and size of the WO₃ nanostructures, respectively. These nanostructured films exhibited enhanced electrochromic performance, and we drew a map for the correlation between the morphology and the electrochromic performance of the as-synthesized WO₃ films. Due to the large tunnels in the hexagonally structured WO₃, and the large active surface area available for electrochemical reactions, a large optical modulation of 66% at 632.8 nm and a potential of −2.0 V, fast switching speeds of 6.7 s and 3.4 s for coloration and bleaching, respectively, and a high coloration efficiency of 106.8 cm² C⁻¹ are achieved for the cylindrical nanorod array film.