Environmental Engineering Reference
In-Depth Information
Figure 9.14
The instability of Showa-Shell CIGS solar panels, reported by
Kushiya
et al.
in2003,duringstabilitystudiesofsolarpanels(re-drawnfrom
ref. [16].
The unstable behaviour of Showa-Shell CIGS solar panels, as
reported by Kushiya
et al.
, is another good example [15]. Although
these Showa-Shell CIGS panels produce large-area modules with
high e
ciencies [16], major features of instabilities are reported in
2003, as shown in Fig. 9.14. It is clear that the light soaking of solar
panels reduces the e
ciency from
∼
11.5% to
∼
8.5%. However,
cooling during the I-V test increases the e
ciency back to their
maximum values of
∼
13.3%. This is mainly due to the quenching
of R&G activities by freezing defect activities at lower temperatures.
The presence of a set of defect levels in the Showa-Shell CIGS
material has been experimentally observed and recently reported
[7]. The identification of the origin of these defect levels and their
removal(orpassivation)willeliminatetheseundesirableinstability
issues andproduce stableand high-e
ciency solar panels.
The usually observed trade-off between the two parameters
V
oc
and
J
sc
can also be understood in terms of defect structures present
in solar cells. The results reported in 2005 by Contreras
et al.
[17]
together with the general observation of improved
V
oc
values with
corresponding reduced
J
sc
could be explained as follows. Whatever,
the device structure used, there exists an active PV junction with a
set of defect levels. As an example, consider the simplest situation
