Civil Engineering Reference
In-Depth Information
''anode'' and ''cathode'' through structural imperfections or other causes, and
repeated electrical ''refresh pulses'' are demanded to maintain the optical prop-
erties during extended periods of time. The ''monolithic'' approach requires means
to protect the electrochromic device from external damage and in practice it must
be incorporated in an insulated glass unit (known as ''IGU'').
A laminated construction embodying two parallel double-layer-coated glass
panes is commercially available since few years (
www.econtrol-glas.de
)
. The
electrolyte is injected as a fluid in a millimeter-wide space between the panes via
vacuum filling and is subsequently solidified. The injection procedure is known to
be a time-consuming process (Xu et al.
2009
).
Another laminated design, described by Kraft and Rottmann (
2009
), employs
an electrolyte based on polyvinyl buteral (PVB)—i.e., a well-known and widely
used material for glass lamination—and transparent electrodes of FTO. The ion-
storage film comprises ferric hexacyanoferrate (''Prussian blue''), which is easy to
deposit by electroplating, whereas, as far as it is known, it cannot be prepared by
standard large-scale glass coating such as magnetron sputtering.
Yet another laminated electrochromic device employs web coating and is
discussed further in the next section.
3.3 Example: A Foil-Based Device Incorporating W Oxide
and Ni Oxide
W oxide is the most widely studied electrochromic material, and it works well in
tandem with Ni oxide in ''battery-type'' devices (Avendaño et al.
2006
; Niklasson
and Granqvist
2007
). The pertinent elements are abundant in the earth's crust and
there are no constraints regarding their availability, which is an essential point for
large-scale implementation of electrochromic glazings.
Several studies of electrochromic devices based on W oxide and Ni oxide have
been reported for glass-based (Mathew et al.
1997
; Larsson and Niklasson
2004
;
Subrahmanyam et al.
2007
; Huang et al.
2011
; Wang et al.
2011
; Chen and Jheng
2012
) and PET-based (Azens et al.
2003c
; Niklasson and Granqvist
2007
;
Granqvist
2012c
) constructions. Combinations of Mo oxide and Ni oxide are
possible too (Lin et al.
2012
). A recent variety of the ''battery-type'' device utilizes
refractive-index modulation in a multilayer structure comprising alternate layers of
W oxide and Ni oxide, in what is effectively a Bragg mirror, to accomplish
reflectance modulation (Redel et al.
2012
).
Figure
14
depicts a specific design of an electrochromic device: One PET foil is
coated with ITO and W oxide, another PET foil is coated with ITO and Ni oxide,
and an ion-conducting adhesive joins the oxide layers. Electrical charge is inserted
and extracted via the ITO films, and then, the mid-luminous transmittance at
k = 0.55 lm is altered as shown in Fig.
15
.
