SW have been steadily developed over the years and as a result there has been rapid development of energy-efficient glazing techniques that promise next-generation architectural windows with energy saving characteristics. These technologies have recently been implemented in large-area glazing (windows and glass facades) in order to create buildings, which combine energy efficiency with good indoor comfort. SW that dynamically modulates light transmittance is crucial for building energy efficiently and promising for on-demand optical devices. The rapid development of technology brings out different categories that have fundamentally different transmittance modulation mechanisms, including the electro-, thermo-, and photochromic SW.
Current challenges focus on the advanced materials design with multi-functionality, low cost, mass production fabrication process and durability. SW have been successfully applied in some demonstration projects or buildings and shown promising applications in those fields, challenges in commercial usage are still present. Firstly, the cost of the SW is high. The estimated payback period can be up to 20 years for both commercial and residential buildings, regardless of the maintenance, repair or replace fee during these periods. Thus, it is urgent demanding to invent cost-effective technology for SW.