Enhanced Electrochromic Properties by Improvement of Crystallinity for Sputtered WO3 Film

Zhu-Jie Xia,Qian Shi,Peng Tang,Hong-Li Wang,Yi-Fan Su,Zhi-Guo Zhang,Ming-Jiang Dai,Huai-Jun Lin

doi:10.3390/coatings10060577

Abstract

Tungsten oxide (WO3) is widely used as a functional material for “smart windows” due to its excellent electrochromic properties, however it is difficult to overcome the conflict between its optical modulation and cyclic stability. In this work, WO3 thin films with different crystal structures were prepared by DC reactive magnetron sputtering method. The effects of substrate temperature on the structure, composition, and electrochromic properties of WO3 films were investigated. The results show that the crystallinity of the WO3 film increases with increasing deposition temperature, indicating that temperature plays an important role in controlling the structure of the WO3 film. For WO3 thin films formed at a substrate temperature of 573 K, the film is in an amorphous state to a crystalline transition state. From X-ray diffraction (XRD) analysis, the thin film showed a weak WO3 crystallization peak, which was in the composite structure of amorphous and nanocrystalline. Which has the best electrochromic properties, with modulation amplitude of 73.1% and bleached state with a coloration efficiency of 42.9 cm2/C at a wavelength of 550 nm. Even after 1500 cycles, the optical modulation still contains 65.4%, delivering the best cyclic stability.

Highlights

With the increase of global challenges related to energy depletion, the development of new energy-saving materials, such as electrochromic (EC) materials attracting people’s attention [1,2,3].Electrochromic materials are capable of reversibly changing their optical properties by switching the applied voltage [4,5,6]
The low intense peaks near 24◦ and 34◦ belonging to WO3 are observed at substrate temperature of 573 K, revealing the crystallinity transition
It can be seen that the intensity of the Bragg reflection increases with the substrate temperature, indicating that the film has higher degree of crystallization at higher substrate temperature [20]

Summary

Introduction

With the increase of global challenges related to energy depletion, the development of new energy-saving materials, such as electrochromic (EC) materials attracting people’s attention [1,2,3]. Electrochromic materials are capable of reversibly changing their optical properties by switching the applied voltage [4,5,6]. Owing to their large optical modulation range and long cycle life, the EC materials can be used as a smart window for energy-saving buildings or antiglare rear-view mirrors for automobiles. Studies have shown that the electrochromic performance of WO3 thin films is closely related to its structure, including geometry, particle size, crystallinity, stoichiometry, etc. It is widely believed that crystalline WO3 thin films have remarkable cyclic stability and low optical modulation range, while

Methods

Results

Conclusion