Environmental Engineering Reference
In-Depth Information
Figure 7.13 Quantum efficiency values
measured in top, middle, and bottom of triple-
junction silicon film cell structure of
Figure 7.12 [93]. The different layers are
deposited as the stainless steel foil substrate
moves continuously through a line of deposition
and processing stations, at a speed of about 2.3
feet/min.
described in Chapter 9. Single-junction silicon cells have an open-circuit voltage
typically less than 0.6 V. Tandem silicon cells are used in the articial leaf that we
will describe in Chapter 9.
This kind of product could be used on the rooftops of New York City as was
discussed in Chapter 5. This manufacturer, Ovonics, LLC, uses silicon, which is
benign environmentally and of unlimited supply (sand is silicon dioxide), and this
manufacturer also has a long history of providing solar tiling for roofs of
apartmentbuildings.Itappearsthatthese
flexible solar panels are available in
10 MWquantities. On the other hand, a lower price and higher ef
ciency
12.5%
might well be obtained with thin-
lm single-junction CdTe cells, also available in
large quantities.
7.2
Organic Molecules as Solar Concentrators
Here (Fig. 7.14) solar cells are mounted vertically on the edges of the light
collecting plates, which have dissolved dyes. The upper plate collects blue
photons, the dye reemits (
(fluoresces) and that light is sent to the cells on the
edge. The
fluorescence quantum ef
ciency of isolated dye molecules approaches
unity. (Total internal reflection helps keep the reemitted light inside the plate,
until absorbed in a solar cell).
