1 has to be fabricated by sol-gel, particular attention must be paid to the
chemistry of the solutions and the firing conditions so that no change occurs in the
microstructure, chemistry, solubilization of the existing layers or formation of a
new undesirable phase at the interface of the coatings. Most of the work reported
on sol-gel coatings for electrochromic devices has been limited to single layers
which may then be incorporated into the device either by physical vapor deposition
of the rest of the stack or by laminating the sol-gel deposited electrodes with an
ion conductor.
Transparent conductive coatings such as indium tin oxide (ITO), doped tin
oxide and zinc oxide are important elements of EC devices. They will not be
covered in this review due to the commercial availability of these coatings on both
glass and plastic substrates. Several references to sol-gel deposition of transparent
conductors are given elsewhere [27]. The literature on individual electrochromic
electrodes and counter electrodes made by sol-gel processing and also the EC
devices where such layers have been incorporated will be reviewed here. We will
also discuss the effect of doping and mixed cations on the performance of these
electrodes, since the sol-gel process is particularly amenable to these modifica-
tions.
3. Electrochromic electrodes
As shown in table 1, a number of materials are used as electrodes in elec-
trochromic devices. Some of these change color, and some of them are only used
for their reversible ion storage properties. Some of the more popular material
choices and the related sol-gel activities are described below.