Recent progress in improving strategies of metal oxide-based electrochromic smart window

The consumption of energy by buildings accounts for 30% of the total amount of social primary energy used, and approximately 30%∼50% of this is lost through windows. To promote energy conservation, the green development of buildings, and revolutionarily upgrade energy production and consumption, developing energy-efficient windows while preserving architectural aesthetics is necessary. Electrochromic smart windows (ESWs) can control the amount of solar energy transmitted into buildings based on personal preference or weather conditions, thereby reducing the amount of energy consumed by buildings for lighting and cooling. The optical transmittance of ESWs is changed by applying different voltages, and they maintain their state without the input of energy. Metal oxides are considered among the most promising electrochromic films for use in ESWs because of their relatively good physical and chemical stabilities. After nearly half a century of development, the practical application of metal oxide-based ESWs is nearly realized. This review presents an evaluation of the performance of ESWs and summarizes five strategies that can be used to enhance the electrochromic properties of metal oxides. These include controlling the oxygen vacancy concentration, doping aliovalent ions, controlling the morphology, selecting the optimal electrolyte, and controlling crystallinity. This review also investigates the development of metal-oxide-based ESWs.