High-Performance Electrochromic Device Based on WO₃/NiO Complementary Characteristic and Highly Porous Structure

Highly porous tungsten trioxide (WO₃) and nickel oxide (NiO) films were prepared by electrodeposition and chemical bath deposition methods, respectively. The two films exhibit good electrochromic properties and cycling durability in LiClO₄/propylene carbonate (PC) electrolyte. The assembled electrochromic device based on WO₃/NiO complementary structure was manufactured for modulating optical transmittance. The electrochromic properties were investigated by means of transmittance spectra, cyclic voltammetry (CV) and chronoamperometry (CA) measurements. It is found that the amorphous WO₃ film exhibits a noticeable electrochromism with a variation of transmittance up to 65.5% at 550 nm, and the highly porous NiO film shows high electrochemical reversibility for Li⁺ insertion/extraction reaction. The electrochromic device shows a large optical modulation of 83.7% at 550 nm, much higher than that of single NiO (38.6%) or WO₃ (65.5%) films. The response time of the device is found to be about 1.76 s for coloration and 1.54 s for bleaching, respectively. These advantages such as large optical modulation, fast switch speed and excellent cycling durability make it attractive for practical applications.