Direct Regulation of O/W Stoichiometric Ratio and Microstructure in Tungsten Oxide Electrochromic Films by Ar Pressure Using Oxide Target Sputtering

Abstract

Herein, amorphous tungsten oxide electrochromic (EC) films are successfully prepared by radiofrequency (RF) magnetron sputtering in pure Ar atmosphere using an oxide target. The effect of Ar pressure on the apparent color, deposition rate, crystal structure, O/W ratio, surface morphology, and EC properties of the as‐deposited tungsten oxide films is systematically investigated using spectroscopic ellipsometry, X‐ray photoelectron spectroscopy, X‐ray diffraction, scanning electron microscopy, and cyclic voltammetry. Interestingly, the Ar gas pressure plays a key role in regulating the O/W ratio, microstructure, and EC properties of the obtained tungsten oxide films. The films are all substoichiometric, and the O/W ratio changes from 2.79 to 2.89 with the increase in Ar pressure. In addition, the loose surface microstructure is shown as Ar pressure increases. The tungsten oxide films deposited at the Ar gas pressure of 1.2 Pa reaches the deposition rate of 13.0 nm min−1, the largest optical modulation of 71.2% at 550 nm, and the EC efficiency of 51.3 cm2 C−1. This film also reveals excellent electrochemical stability and sustains more than 200 cycles. These results provide a simple solution for preparing high‐quality tungsten oxide EC films using oxide ceramic targets in pure Ar atmosphere.