Environmental Engineering Reference
In-Depth Information
passivated native oxide (quartz) layer. This article also details a polycrystalline Si solar
cell of 19.8% ef
ciency with a honeycomb texturing of the upper surface.
These authors found that completely enclosing the Si surface with thin thermal
oxide to reduce recombination improved cell ef
ciency. However, the thermal oxide
must be thin, on the order of 20 nm, so that the antire
ection double layer applied
above the oxide will still operate correctly. The polycrystalline version of this cell was
grown on 1.5
min
thickness. The use of diffused highly doped material just belowmetallic contacts, on
front and back, suppresses recombination by repelling the minority carriers.
It was also reported that the Si/SiO
2
interfaces could be improved, passivated to
reduce recombination of electrons and holes, by exposure to atomic hydrogen. Thus,
the record-ef
ciency cell is denoted PERL (passivated emitter, rear locally diffused
cell).
A large installation of single-crystal solar cells is shown in Figure 6.6, located at
Nellis Air Force Base in the United States. This array provides 15MWof power, and is
shown to track the suns motion in one direction.
The second example of a large solar panel installation, this time based on
polycrystalline silicon (Dell Jones (2011) Regenesis Power, personal communica-
tion.), is suggested on the cover of this topic, the lower right image. This view is
similar to panels in a 2MW
V
m, large-grained directionally solidi
ed P-type silicon 260
m
field of 185WMitsubishi Electric modules, covering 16
acres, installed at the Florida Gulf Coast University in 2008. These modules are rated
at 13.4% ef
ciency, and each consists of 50 cells of dimension 15.6 cm
15.6 cm.
These cells are thus similar to the silicon cells described above.
Figure 6.6 Nellis Air Force Base panels track the sun in one axis. Large conventional single-crystal
silicon installation (http://en.wikipedia.org/wiki/File:Nellis_AFB_Solar_panels.jpg).
