Trends in sputter deposited tungsten oxide structures for electrochromic applications: A review

Electrochromic devices (ECD) show reversible color change under applied electric field and are predicted to become indispensable in many applications such as low power displays, smart windows to develop energy-saving buildings as well as light-adapting mirrors in high-end cars and aircrafts. Despite the assiduous research work, ECD faces several challenges for practical usage including delamination, durability, lifetime and their integration into multifunctional devices. To improve the performance, different techniques have already been used to deposit single-layered thin film, or a stack of promising EC layers on several substrates including transparent conductive oxides (TCO) coated glass and different conducting polymers. These layers can be flat enough or have a definite shape or structure to satisfy the needs of the designed device. Based on their low resistivity and high transparency, fluorine and indium doped tin oxides (FTO, ITO) are mostly used as TCOs whereas polyaniline, polypyrrole and ethylenedioxythiophene are the trending future polymers. In this review, the critical parameters of magnetron sputtering are delineated for the deposited tungsten oxide (WO3) films focused on ITO and FTO layered glass. The main focus of interest is to highlight the recent progress and future trends in this technique, structure introduced with sputtered electrochromic film and their carefully review along with effect of altering these parameters on physical, optical, electrochemical, durability and thus overall performance of the ECD. Finally, it will be intended to underline the future perspectives in realizing smart EC devices with various factual characteristics.