Electrically Triggered Color-Changing Materials: Mechanisms, Performances, and Applications

Electrically triggered color-changing materials, termed as electrochromic materials, offer precise and programmable color transistions through the manipulation of electric field frequency and amplitude. They are used as displays, sensors, military camouflage, wearable devices, and anticounterfeiting materials. Their future advancements depend on clear understanding of the color change mechanisms and pros/cons between different electrochromic materials. To this end, we starts by categorizing electrochromism into two classes according to color production mechanism: chemical color-based and physical color-based. Within the former, color emerges from chemical molecules selectively absorbing specific wavelengths of light and color changes stem from electrochemical redox reactions. The latter, meanwhile, hinges upon electrically induced alterations in the geometries, dimensions, or arrangements of nano/micro structures, such as photonic crystals and plasmonic nanostructures. The principles of color changes in both categories are detailed, and compare their differences in terms of response time, operating voltage, degree of color change, and stability. At the end, their applications will be discussed spanning from smart windows to color display, dynamic camouflage, energy storage, and thermal management. This critical review is aimed to provide multidisciplinary insights that will benefit both novices and seasoned experts engaged in fundamental exploration or practical investigations of electrochromic materials. Electrochromic materials, triggered by electricity, enable precise color shifts for wide applications. The electrochromism are first classified into chemical and physical color-based by revealing their distinct color change mechanisms. Then their electrochromic performances are compared and discussed their applications from smart windows to displays and energy storage. Finally, insights are shared on the future direction of the field.image