Environmental Engineering Reference
In-Depth Information
Figure 6.14 Quantum efficiency of CIGS solar
cells [79]: solid curve, CIGS thickness 1
100 nm MgF
2
after depositing the 200 nm thick
window layer of Al-doped ZnO, which exhibited
a sheet resistance 65
m
m
(17.2% efficiency); dashed curve, CIGS
thickness 2.5
70
V
/square, and a Ni/Al
-
m (18.7% efficiency). These cells
benefit from a final antireflection coating of
m
grid to collect current.
by immersion for 13min in a 60
C bath composed of 1.5mM CdSO4, 1.5M
NH4OH, and 75mM thiourea.
The authors report nuances in the method of coevaporation of the absorber to
accomplish bandgap grading, and also suggest that for CIGS layer thickness below
1
m the deep-level density increases. For this reason, mobility and lifetime are
reducedwhen the thickness is reduced to 0.5
m
m. This speci
c process is not scalable,
but demonstrates a high ef
ciency, 19.9%, in single-junction CIGS solar cells.
The European
firm Avancis has produced 15.8% ef
cient CIGS modules using a
more conventional linear process. It appears that the
firms using the ink process have
not won customers, and, in fact, the total production of theCIGS cells is small compared
to the production of CdTe cells, which presently dominate the thin-
lmsolar cell market.
m
6.4
CdTe Thin-Film Cells
The largest thin-
lm solar cell supplier is First Solar, manufacturing thin-
lm cells of
CdTe. According to the
New York Times
[80], First Solar, an American
firm based in
Tempe, Arizona, has signed an agreement with the Chinese government for a 2 GW
photovoltaic farm to be built in the Mongolian desert.
The photovoltaic farm of area 25 square miles is part of a 11.9GW renewable
energy park to be built at Ordos City in Inner Mongolia. The overall project is to
include 6.95 GWof wind power, 3.9GWof photovoltaic power, and 0.72GWof solar
