Improvement on cyclic stability for flexible tungsten oxide electrochromic film by covering an 18 nm zinc-tin-oxide buffer layer

Abstract

Herein, we firstly reveal the feasibility that amorphous zinc tin oxide (ZTO) can be employed as buffer layer to improve the cyclic stability for the room-temperature sputtered tungsten oxide electrochromic (EC) film on flexible PET substrate. In this primary work, a ZTO layer with a thickness of 18 nm was radio frequency (RF) sputtered on the surface of 300 nm thick tungsten oxide film, and the corresponding characterizations on composition, structure and EC performance were carried out by XPS, XRD, SEM and electrochemical analysis. It was found that the introduction of ZTO buffer layer maintained a stable nano-column structure and prevented a structural degradation during the harsh Li+ insertion/extraction in EC process, and then restrained the deterioration in colored transmittance (Tc) and optical modulation (ΔT). After 2000 electrochemical cycles, there was a little change in Tc, ranged from 3.6% to 8.7% (at 790 nm), and the related ΔT variation was only from 78.6% to 76.8% (at 790 nm). As a comparison, under the same optical wavelength, the sample without ZTO buffer layer had a Tc range from 3.1% to 21.4% and ΔT variation from 80.0% to 65.3%. This superior EC stability make this novel bilayer structure promising for future commercial application in high quality EC devices.