elektrokromismi

Elektrokromismi is a class of phenomena in which a material changes its color or opacity in response to an electrical stimulus and then reverses when the stimulus is removed. In electrochromic devices the applied voltage induces a redox reaction or ion intercalation that alters the electronic structure and light absorption of the material.

Typical electrochromic devices use a laminated stack: a transparent conducting electrode, an electrochromic layer, an ion-conducting electrolyte, and a counter electrode, all sealed between glass or flexible substrates. When voltage is applied, ions migrate into the electrochromic layer and cause a change in oxidation state; this changes visible light absorption and the material darkens or lightens. Reversing the voltage or removing it drives ions back and restores the original color.

Materials used span inorganic oxides like tungsten oxide (WO3) and nickel oxide, and organic systems such as viologens and conducting polymers (for example polyaniline and polypyrrole). Prussian blue and related redox compounds are also used. Device performance is described by parameters such as optical contrast, switching speed, coloration efficiency, cycling stability, and the required operating voltage.

Common applications include smart windows for buildings, automotive and architectural glazing, rear-view mirrors with adjustable tint, and some display technologies. Elektrokromismi offers controllable shading with potential energy savings by reducing heating and lighting loads, but challenges remain in durability, cost, and long-term stability of devices.