Preparation And Properties Of WO₃ And NiO Complementary Electrochromic Films And Device

NiO film is considered as a potential electrochromic material due to its excellent electrochromic properties. Amorphous WO₃ film is a typical cathodic electrochromic material as the electrochromic layer of an electrochromic device. The electrochromic device consisting of NiO and WO₃ films greatly simplifies the fabrication procedure and exhibits better performance than the traditional device, which offers wide application.We developed a facile and high efficiency chemical bath deposition method for preparing porous NiO films. The effect of annealing temperatures on the structure and electrochromic properties is discussed. The as-prepared NiO film exhibits a highly porous structure made up of interconnected nanoflakes with a thickness of 20–25 nm. The NiO film annealed at 300°C shows the best electrochromic properties with an optical modulation of 38.6% in the visible region. With the increasing of annealing temperature, the electrochromic properties become worse.The WO₃ films were prepared by electrodeposition method. The effect of annealing temperature on the structure and electrochromic properties is discussed. The WO₃ film annealed at 250°C is amorphous and porous, exhibits a noticeable electrochromism with an optical modulation of 65.5 % at 550 nm. The WO₃ films annealed at 300°C and 350°C are crystallized with a compact structure and a poor electrochromic performance. With the increasing of annealing temperature, the WO₃ films are better crystallized, but the electrochromic properties become worse.An electrochromic device based on the NiO/WO₃ complementary structure was manufactured for modulating the optical transmittance. The electrochromic device shows good electrochromic performance, reversibility and stability, and an optical modulation of 83.7 % at 550 nm. The response time of EC device is found to be about 1.76 s for coloration and 1.54 s for bleaching (E₁ =2 V, E₂ =-2V). The coloring current is almost the same as the bleaching current and the current-time response curves remain unchanged during the long-term cycling.