Civil Engineering Reference
In-Depth Information
The second point is that the transparent conductors must combine high elec-
trical conductivity, low luminous absorptance, and excellent durability, which is
challenging especially for temperature-sensitive substrates such as PET. For the
time being (2013), ITO coatings may still be the best option, but metal-based
alternatives are very promising.
As a third item, one should consider the electrochromic device as an electrical
battery, and then, the question of how to introduce the electrical charge, and its
balancing between the ''anode'' and ''cathode,'' stands out as essential processes.
Gas treatments have been developed for these purposes (Azens et al.
2003b
;
Aydogdu et al.
2010
), but other means are available too.
Fourthly, the electrolyte is critical. If it is a thin film, it must be made under
conditions that avoid pinholes and other causes of short-circuiting between the
electrochromic film and the counter-electrode; if it is a polymer, it must be stable
under ultraviolet irradiation and also serve as a reliable adhesive between the two
parts of the electrochromic device. Nanoparticle-based functionalization is a newly
introduced asset for the latter type of electrolyte, as discussed above in
Sect. 2.5
.
The fifth challenge concerns long-term cycling and storing durability, which
again points at the kinship with electrical batteries. Simple switching between two
voltage levels is commonplace in university-based research, but much more
elaborate procedures may be required for electrochromic glazings to be used in
buildings as discussed by Degerman Engfeldt et al. (
2011
).
The sixth and final item considered here concerns the possibility to accomplish
large-scale, low-cost manufacturing. To this end, it is necessary to avoid time-
consuming steps such as protracted thin-film deposition, extended post-treatment,
separate electrochemical steps for charge insertion and extraction, slow intro-
duction of electrolyte. Roll-to-roll deposition onto web-type substrates (Bishop
2010
,
2011
) in conjunction with continuous lamination procedures may be
favorable techniques for cheap electrochromic glazing, as further elaborated in
Sect. 3.3
.
3.2 Survey Over Some Practical ''Battery-Type''
Electrochromic Devices
We now consider a number of alternative constructions for ''battery-type'' elec-
trochromic devices. In fact, there are numerous of these mentioned in the scientific
and technical literature published during several decades, but only a few of them
can be considered ready for practical applications (Granqvist
2008a
,
2012a
;
Baetens et al.
2010
, Jelle et al.
2012
).
Five-layer ''monolithic'' device designs on a single glass pane have been
developed by several companies (
www.sageglass.com
,
www.soladigm.com
).
Their details remain proprietary, but it is apparent that the electrolyte is a thin film.
This construction makes it very difficult to avoid some leakage current between the
