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Tungsten oxide (WO3) is a transition metal oxide with a wide range of applications such as displays, rear-view mirrors, electrochromic (EC) smart windows and gas sensors. Many techniques were adopted for the fabrication of WO3, namely magnetron sputtering, spray pyrolysis and sol-gel synthesis techniques. In this work, WO3films were deposited on indium tin oxide (ITO) coated glasses by sol-gel spin-coating method. The film thickness was varied by depositing different number of layers. The WO3film thickness and optical transmittance were determined using step profilometer and ultraviolet-visible (UV-Vis) spectrophotometer, respectively. WO3film thicknesses increased from 38 nm to 606 nmwith increasing number of deposited layers.The optical transmittance of the WO3films in visible range decreased with increasing film thickness. The optical transmittance were at least 70 % up to 10 deposited layers.WO3is a promising EC material in the application ofEC devices (ECDs).The application of WO3in the EC devices will be discussed.

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In order to curb high electricity usage, especially in commercial buildings, smart windows, also known as “switchable” or “smart” glasses, have attracted a significant amount of attention in an effort to achieve energy savings in eco-friendly buildings and transportation systems. Smart windows save energy by regulating the input of solar heat and light and hence cutting down air-conditioning expenses, while maintaining indoor comfort. This is achieved by electrochromism, which is defined as the reversible colour change in electrochromic (EC) materials from transparent to dark blue and vice versa under a small applied voltage. Recent state-of-the-art electrochromic devices (ECD) adopt liquid-based electrolytes as the main source of energy for basic operations. While this has resulted in much success in ECDs as reported in past studies, there remain several drawbacks to this aspect, such as liquid electrolyte leakage and evaporation, not to mention safety concerns related to the harmful nature of electrolyte materials. This paper aims to review the recent advances in various solid electrolytes that are potential solutions to the mentioned problems.

Tungsten oxide (WO 3 ) is an n-type semiconductor with a wide range of transparent electronic applications such as smart windows, rear-view displays and gas sensors. In this work, WO 3 films were prepared on tin doped indium oxide (ITO) coated glasses by utilising the sol-gel spincoating method. The effect of WO 3 precursor solution stirring time (3, 10 and 24 h) on the electrochromic (EC) properties of WO 3 films was investigated. The optical transmittance of the WO 3 films in the visible range decreased as precursor stirring time was increased. The WO 3 films subjected to 3 and 10 h of stirring had a large optical modulation compared to the WO 3 films subjected to 24 h of stirring. CV results showed higher coloration current in WO 3 films subjected to 3 h stirring which is an indication of faster intercalation kinetics. Moreover, it had fast switching time and high coloration efficiency of 34.8 cm 2 C -1 .