ABSTRACT
As the name implies, electrochromics are simply materials, substances, or devices which change color when a voltage (or very rarely, a current) is applied (classical Greek e´lhktron, amber, croma, color). The reader may think for the moment of the photochromic sunglasses worn by many, especially the elderly, which change color from clear to dark in bright sunlight. If one substitutes the activation of these sunglasses using bright sunlight by activation using a small (±5 V) DC voltage from a battery placed behind the ear, then one has arrived at an electrochromic device, here, electrochromic sunglasses. To this rather simple defi nition for electrochromism, “color change with applied voltage,” we can add a somewhat broader one, “change of color or spectral signature, with applied voltage or equilibrium potential or chemical potential.”
