Enhanced electrochromic properties of Ag-incorporated WO3 nanocomposite thin films

Abstract

WO3 nanocomposite thin films, in which metal nanoparticles are incorporated into a WO3 matrix, offer an enhanced electrochromic response speed with color neutrality. This article reports the structural, optical, and electrochemical properties of Ag nanoparticle-incorporated electrochromic WO3 thin films with different con-centrations. Room-temperature-sputtered thin films using composite targets with a low Ag concentration exhibited a random distribution of small nanoparticles. In contrast, in the film with a higher Ag concentration, the particles were merged, resulting in a single or polycrystalline phase. Surface plasmon resonance peaks were observed in the absorption spectra of the Ag-WO3 composite films, indicating the formation of metallic nano -particles, which was also confirmed via high-resolution transmission electron microscopy. The optical bandgaps decreased gradually from 3.15 eV for WO3-delta to 3.02 and 2.99 eV for W0.97Ag0.03O3-delta and W0.91Ag0.09O3-delta thin films, respectively. The W0.91Ag0.09O3-delta thin film showed a faster switching time of 2.6 s for coloring and 4.8 s for bleaching with a higher coloration efficiency of 66.52 cm2/C than those of the WO3-delta thin film, which were 3.8 s, 6.8 s, and 58.68 cm2/C, respectively. However, transmittance modulation in the W0.91Ag0.09O3-delta thin film was inferior to that in the other films. Furthermore, the W0.91Ag0.09O3-delta thin films were black in the colored state, whereas the bare WO3-delta and W0.97Ag0.03O3-delta thin films were Prussian blue, suggesting the realization of color neutrality through the incorporation of Ag nanoparticles.