Preparation and Properties of WO3 and NiO Complementary Electrochromic Films and Device
|School||Zhejiang University of Technology|
|Course||Materials Physics and Chemistry|
|Keywords||Electrochromism Porous thin film NiO WO3 Electrochromic 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.