Civil Engineering Reference
In-Depth Information
known, but it is evident that the electrolyte is a very thin layer. By this
arrangement it is very hard to eliminate some leakage ('trickle') current
between the electrochromic fi lms via structural imperfections, and
repeated electrical 'refresh pulses' are needed to maintain the window
in a constant, darkened state; furthermore, coloration and bleaching
may proceed unevenly over large areas.
•
A laminated design with two parallel double-layer-coated glass panes
joined by a polymer electrolyte is available on the market in limited
quantities. Here the electrolyte is injected in fl uid form in a millimeter-
wide gap between two glass panes via vacuum fi lling, which is a time-
consuming process (Xu
et al.
, 2009).
•
A second laminated design (Kraft and Rottmann, 2009) makes use of
an electrolyte based on polyvinyl buteral (PVB), which is a standard
material for glass lamination, and transparent electrical conductors
of fl uorine-doped tin oxide made by low-cost spray pyrolysis in
conjunction with fl oat glass production. The ion storage fi lm is of ferric
hexacyanoferrate ('Prussian Blue'), which is possible to prepare via
electro-deposition but, as far as is known, not by standard glass coating
techniques such as magnetron sputtering; this fi lm is a conductor for K
+
ions (de Tacconi
et al.
, 2003).
•
Still another laminated design is different from the others in being based
on fl exible polyethylene terephthalate (PET) foil and hence allowing
low-cost roll-to-roll web coating (Azens
et al.
, 2003b; Niklasson and
Granqvist, 2007). One PET foil is coated with transparent and conduct-
ing indium-tin oxide (ITO) and electrochromic tungsten oxide, another
PET foil is coated with ITO and an electrochromic nickel-based oxide,
and the coated surfaces of the two foils are joined via an electrolyte
applied by continuous lamination. The foil can be used as an add-on for
upgrading existing windows, as a suspended electrochromic 'third pane'
in an insulating glass unit, or as a lamination joining two glass panes.
This type of electrochromic glazing is discussed further below in Section
11.3.5.
There are numerous alternative electrochromic device designs as well,
both based on an oxide-based 'battery' approach as in Fig. 11.1 and others.
Considering fi rst the 'battery' type, one may note that there are non-oxide
inorganic electrochromic materials, and 'Prussian Blue' (de Tacconi
et al.
,
2003) was mentioned above. Furthermore, electrochromism is a common
phenomenon in organic materials, and a vast literature exists on this subject
(Monk
et al.
, 2007). Their durability under irradiation is much less than for
the oxides, but the coloration effi ciency (the change in optical absorption
per unit of charge exchange) can be much higher in organic materials than
in oxides. Metal hydrides represent another option and can display variable
Search WWH ::
Custom Search