Introduction

While the applications of electrochromism are ever growing, all devices utilising electrochromic colour modulation fall within two broad, overlapping categories according to the mode of operation: electrochromic devices (ECDs) operating by transmission (see schematic in Figure 13.1) or by reflection (see the schematic representation in Figure 13.2).

Several thousand patents have been filed to describe various electrochromic species and devices deemed worthy of commercial exploitation, so the field is vast. Much duplication is certain in such patents, but it is clear how large scale are the investments directed toward implementing electrochromism as viable in displays or light modulation. In this field, vital details of compositions are often well hidden, as these comprise the valued intellectual property rights on which substantial financial considerations rest.

The most common applications are electrochromic mirrors and windows, as below. These and other applications are reviewed at length by Lampert (1998), who cites all the principal manufacturers of electrochromic goods worldwide, and also several novel applications.

Reflective electrochromic devices: electrochromic car mirrors

Mirrors, which obviously operate in a reflectance mode, illustrate the first application of electrochromism (cf. Figure 13.2). Self-darkening electrochromic mirrors, for automotive use at night, disallow the lights of following vehicles to dazzle by reflection from the driver's or the door mirror. Here an optically absorbing electrochromic colour is evoked over the reflecting surface, reducing reflection intensity and thereby alleviating driver discomfort. However, total opacity is to be avoided as muted reflection must persist in the darkened state.