Effects of Annealing Temperature on Optical Band Gap of Sol-gel Tungsten Trioxide Films

Abstract

Tungsten trioxide (WO3) is a wide band gap semiconductor material that is used as an important electrochromic layer in electrochromic devices. In this work, the effects of the annealing temperature on the optical band gap of sol-gel WO3 films were investigated. X-ray Diffraction (XRD) showed that WO3 films were amorphous after being annealed at 100 °C, 200 °C and 300 °C, respectively, but became crystallized at 400 °C and 500 °C. An atomic force microscope (AFM) showed that the crystalline WO3 films were rougher than the amorphous WO3 films (annealed at 200 °C and 300 °C). An ultraviolet spectrophotometer showed that the optical band gap of the WO3 films decreased from 3.62 eV to 3.30 eV with the increase in the annealing temperature. When the Li+ was injected into WO3 film in the electrochromic reaction, the optical band gap of the WO3 films decreased. The correlation between the optical band gap and the electrical properties of the WO3 films was found in the electrochromic test by analyzing the change in the response time and the current density. The decrease in the optical band gap demonstrates that the conductivity increases with the corresponding increase in the annealing temperature.

Temperature-Controlled Crystal Size of Wide Band Gap Nickel Oxide and Its Application in Electrochromism

“…In sol-gel technology, a key parameter is annealing temperature [ 21 ], which is critical in controlling the microstructure and electrochromic properties of the films. In this paper, the microstructure, electrical properties, optical modulation capabilities, and coloring efficiency of sol gel prepared nickel oxide films obtained under different annealing temperatures were analyzed, and the results may improve the current understanding of the relationship between the microstructure and performance of such oxide films.…”

Effect of the Ammonium Tungsten Precursor Solution with the Modification of Glycerol on Wide Band Gap WO3 Thin Film and Its Electrochromic Properties

“…Tungsten trioxide (WO 3 ), the most widely studied and used electrochromic material, has been studied for many years since having been found by Deb in the 1960s, thanks to its attractive characteristics of high coloring efficiency, good optical modulation ability and decent chemical stability in the field of electrochromism [3][4][5][6]. It is remarkable that WO 3 with various crystalline structures by different synthesis methods is extensively appropriate for diverse device applications [7][8][9], such as the electrochromic smart window [10,11], rear-view automatic-dimming rearview mirror [12], gas sensor device [13][14][15], and military camouflage [16], etc. A large variety of techniques can be used to prepare WO 3 thin films, such as chemical vapor deposition (CVD) [17], physical vapor deposition (PVD) [18] and wet chemical deposition methods base on solution [19][20][21].…”

PRODUCTION OF NANOCOMPOSITE WO3/rGO ELECTROCHROMIC FILMS BY THE METHOD OF SPRAY-PYROLYSIS ON GLASS ITO SUBSTRATES

“…Из всех многообразных неорганических электрохромных соединений ученые наиболее часто исследуют WO 3 , который обладает рядом уникальных электро-хромных свойств [4][5][6]. Высокая функциональность, эффективность окрашивания, химическая стабильность, хороший эффект памяти и срок службы делают WO 3 универсальным для практического применения.…”

“…Развитие тонкопленочной технологии позволяет получать различные конфигурации электрохромных пленок [10; 11]. Существует широкий выбор методов получения электрохромных пленок WO 3 , например химическое осаждение из паровой фазы [1], вакуумное испарение [2], механическое напыление [8], золь-гель метод [5] и др. Однако отсутствует универсальная технология, удовлетворяющая всем существующим требованиям.…”