Civil Engineering Reference
In-Depth Information
present or not in rooms equipped with such glazing. Under unfavorable conditions,
some recent modeling results indicate that electrochromic glazing may even
increase the energy consumption (Katanbafnasab and Abu-Hijleh
2013
).
2 Materials for Electrochromic Glazings
The original discovery of electrochromism was made through studies of vacuum-
deposited tungsten oxide films during the 1960s and 1970s (Deb
1973
,
1995
,
2008
;
Granqvist
1995
,
2000
). Display devices were of primary interest in the beginning,
but the focus was then shifted to energy-efficient glazings—referred to as ''smart
windows'' by Svensson and Granqvist (
1986
)—as it gradually became clear that
electrochromic technology could be used for energy savings in buildings. How-
ever, display applications are presently making a strong comeback for applications
in ''electronic paper'' and, more generally, in transparent electronics. The displays
can make good use of organic electrochromic materials (Beaujuge and Reynolds
2010
; Jensen et al.
2012
). The organics are generally regarded as too fragile under
ultraviolet light to be useful in glazings, though, and hence, they are not discussed
further below.
Parts of
Sect. 2
deal with material science issues, and
Sects. 2.2
,
2.3
, and
2.5
are
intended for readers with a special interest in these aspects; they are not necessary
to get an overall view on electrochromic glazings.
2.1 How Does It Work? Basic Device Design and Typical
Materials
Figure
2
shows a typical design of an electrochromic device (Granqvist
1995
).
Five layers are backed by one transparent substrate or are positioned between two
such substrates in a laminate configuration. The substrate is transparent and typ-
ically of glass or flexible polyethylene terephthalate (PET) foil. In an idealized
case, the centrally positioned layer is a pure ion conductor (electrolyte), either a
thin-film or a polymer electrolyte. Its ions should be small in order to be easily
mobile, with protons (H
+
) and Li
+
being the most common choices.
The electrolyte joins an electrochromic film—which is a mixed conductor for
both ions and electrons—and an ion-storage film which in most cases also has
electrochromic properties. This three-layer stack is positioned between two
transparent and electrically conducting thin films. Applying a voltage between the
transparent conductors leads to ion exchange between the electrochromic and
ion-storage films, and charge balance is maintained via a counter-flow of electrons
in the external circuit and electron injection and extraction in the electrochromic
and ion-storage films via the transparent conductors. Voltage reversal or, provided
