Fabrication of Nickel-Doped Tungsten Trioxide Thin Film-Based Highly Stable Flexible Electrochromic Devices for Smart Window Applications

In this study, we fabricated nickel (Ni)-doped tungsten trioxide (Ni-WO3) thin films using the sol–gel method. Different weight percentages (0, 0.1, 0.3, 0.5, 0.7, and 1.0%) of Ni were used to prepare different Ni-doped WO3 samples. Various characterization techniques such as scanning electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy were adopted to confirm the formation of the Ni-doped WO3 samples. We also fabricated WO3- and Ni-WO3 [Ni(0.1)WO3, Ni(0.3)WO3, and Ni(0.5)WO3]-based flexible electrochromic devices (ECDs) on indium tin oxide-coated polyethylene terephthalate substrates. The WO3-based ECDs exhibited a coloration efficiency (CE) of 41.5 cm2/C with an optical contrast of 66.2%, while Ni(0.5)WO3-based ECDs showed a higher CE of 60.62 cm2/C with an adequate optical contrast of 78.31%. Further, Ni(0.5)WO3-based ECDs exhibited excellent cyclic stability up to 25,000 cycles and adequate bending stability up to 1000 cycles.