Civil Engineering Reference
In-Depth Information
1. The electrochromic and counter electrode fi lms must have well-defi ned
nanoporosity over large areas, which requires non-conventional deposi-
tion technologies, which we return to in Section 11.2.3 below.
2. The transparent conductors must have excellent electrical conductivity
jointly with optical transparency, which is demanding particularly for
temperature-sensitive substrates; this part of the electrochromic device
may be the most expensive one, so great care must be exercised in the
choice of material and deposition technology, as further discussed in
Section 11.2.4.
3. Describing the electrochromic device as a thin fi lm battery points at the
fact that insertion/extraction and charge balancing are vital processes;
they may be based on controllable and industrially viable techniques
such as gas treatments (Azens
et al.
, 2003a; Aydogdu
et al.
, 2010).
4. The electrolyte must combine good ion conductivity with excellent
electrical insulation and high stability under ultraviolet irradiation; for
laminated designs, it must also serve as a reliable adhesive.
5. Long-term cycling durability hinges on appropriate strategies for
voltage and current control, just as in battery technology, and simple
switching between two voltage levels, as is common in academic work
on electrochromics, falls very short of an optimized strategy (Degerman
Engfeldt
et al.
, 2011).
6.
Large-scale manufacturing is the key to cost-effective electrochromic
glazings and hence to their market acceptability. Obviously one must
avoid time-consuming production steps such as extended thin fi lm depo-
sition, long post-treatment times, separate steps for electrochemical
charge insertion/extraction, slow introduction of electrolytes, etc. Roll-
to-roll coating of fl exible substrates, followed by continuous lamination,
offer particular advantages, and Section 11.2.5 below discusses the state-
of-the-art for electrochromic devices based on such technologies.
11.2.2 Practical constructions of electrochromic glazings
The scientifi c and technical literature show many examples of electrochro-
mic glazings of various sizes and has done so for decades, but few of these
examples can be considered as products ready for the market or even pro-
totypes. A number of those that are currently (2012) being delivered to
customers on a very limited scale, or at least shown to customers, are intro-
duced next (see also recent articles by Baetens
et al.
, 2010a, and Jelle
et al.
,
2012). All of these products or prototypes rely on electrochromic tungsten
oxide fi lms for at least some of the coloration.
• A fi ve-layer 'monolithic' electrochromic device design on a single glass
pane has been developed by several companies. The details are not
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