Electrochromic

Electrochromic refers to materials and devices that change their optical properties in response to an applied electric field or voltage. The effect arises from reversible redox reactions within the material that modify light absorption, producing a visible color change without continuous power after switching. In practice, electrochromic materials are used in devices composed of a transparent electrode pair, an electrolyte, and an electrochromic layer, forming a stack that can switch between bleached and colored states.

Common inorganic electrochromic materials include tungsten oxide (WO3), which becomes colored upon reduction, and nickel oxide, Prussian blue, and mixed metal oxides. Organic electrochromic systems use conducting polymers such as polyaniline and polypyrrole, or viologen-based compounds. Many devices employ a lithium- or hydrogen-ion conducting electrolyte, and ions shuttle between the electrochromic layer and a counter electrode during switching.

Applications include smart windows and architectural glass, variable-tint rearview and side mirrors, and displays. Advantages include low power consumption, since only brief current is needed to switch states, and non-volatile coloration. Limitations involve switching speed for some materials, limited color range and transmittance control, long-term durability, and the need for robust sealing of the electrolyte.

Research directions focus on faster switching, broader color palettes, higher contrast, solid-state and flexible electrochromic films, and integration with energy storage or sensor functionality. Electrochromic technology has matured into commercial devices in automotive and architectural sectors and remains an active area of materials science.