Growth of vertically aligned hierarchical WO3 nano-architecture arrays on transparent conducting substrates with outstanding electrochromic performance

Vertically aligned hierarchical WO3 nano-architectures on transparent conducting substrate (3×2.5 cm2 in size and sheet resistance Rs=10 Ω) are produced via a template-free solvothermal method. The nanostructured array films with thicknesses of about 1.1 μm show remarkable enhancement of the electrochromic properties in visible spectrum and infrared region. In particular, a significant optical modulation (66.5% and 66.0% at 633 nm, 73.8% and 53.9% at 2000 nm, 57.7% and 51.7% at 8 μm), fast switching speed (4.6 s/3.6 s and 2.0 s/3.4 s), high coloration efficiency (126 and 120 cm2 C−1 at 633 nm) and excellent cycling stability (maintained 77.5% and 81.7% of the initial optical modulation after 4500-cycles) are achieved for the nanotree and nanowire arrays, respectively. The improved electrochromic properties are mainly attributed to the vertically aligned structure and the porous space among the nanotrees or nanowires, which make the diffusion of H+ in these arrays easier and also supply larger surface area for charge-transfer reactions.