Environmental Engineering Reference
In-Depth Information
9.5 Variations in CIGS Solar Cells
Comprehensive work on electrodeposited CIGS-based solar cells
also shows different shapes of I-V curves for different batches of
devices, similar to those of CdTe-based solar cells. These different
types of I-V curves are sketched in Fig. 9.13, and three major groups
are labelled as curves A, B, and C. Curve A represents the desired
solar cell characteristics, observed when the defect concentrations
are low or inactive in the device structure. The other extreme is
shown by curve C, where the photo-generated charge carriers are
removed drastically by defects through the recombination process
and, hence, the current in the external circuit is low and the FF
reduces drastically. The amount of recombination varies according
to the defect levels present, their location and concentrations,
and the Fermi-level position at the interface. Depending on the
circumstances, any shape between A and C could be measured. The
special situation shown by curve B is also observed, but this linear
behaviourisonlyoneofthemanypossibilitiesandnotduetohigher
series resistance of the device structure. Similar results have been
reportedbyPlatzer-Bjorkman
et al.
[14]forsolarcellsbasedonCIGS
grown by the vacuum evaporation method.
Figure 9.13
Different shapes of I-V curves observed for solar cells based
on electrodeposited CdTe and CIGS materials.
