Switchable Glazing Technology: Electrochromic Fenestration for Energy-Efficient Buildings - Nearly Zero Energy Building Refurbishment - page 591

Fig. 14 Principle construction of an electrochromic foil-based device. The entire foil can be
used to laminate glass panes, as indicated in the left-hand part
The upper panel refers to the first 1,000 coloration/bleaching cycles driven via
an electronic circuit that limits the transmittance at both high and low ends of the
transmittance range; the lower setting was deliberately changed after *70 cycles.
The devices operate well for tens of thousands of cycles without essential loss of
performance. The lower panel in Fig. 15 illustrates the coloration dynamics during
a single coloration/bleaching cycle, and it is evident that the main part of the
optical modulation takes place during a few seconds for a device that is 5 9 5cm 2
in size. Larger devices have slower dynamics, and the relevant timescale may be
some ten minutes for an electrochromic glazing on the scale of square meters. The
latter time is suitable for practical fenestration since it allows the human eye to
adapt to varying levels of illumination.
Different optical modulation ranges are of interest depending on the application
of the electrochromic device. For energy control of buildings, one may put a pre-
mium on a large bleached-state transmittance, and antireflection coatings may then
be of interest (Jonsson and Roos 2010 ; Jonsson et al. 2010 ). However, if glare control
is essential, it is possible to achieve a colored-state transmittance in the one-percent
level or lower by putting two or more electrochromic foils on top of each other.
Figure 16 illustrates the performance of a double-layer foil (Granqvist 2008a ).
Low-cost, large-area manufacturing is a must if electrochromic glazing is going
to be used on a large scale. In this context, it is important to note that the foil-type
devices described above can be made by roll-to-roll deposition followed by
lamination (Granqvist 2012c ) and that it is possible to implement a free-form
design concept—with post-deposition electrical contacting—to any shape and size
consistent with the primary foil manufacturing. This latter option is not easily