Page 264 - Mirjam-Theelen-Degradation-of-CIGS-solar-cells
P. 264
Chapter 9
The impact of two methods to make CIGS modules, showed that both methods have
their vulnerabilities: In monolithically integrated modules, the molybdenum and
the zinc oxide present in especially P2 and also in P3 in were shown to be unstable,
leading to increased series resistance. When grid connected modules are considered,
it seemed that nickel covered grids have a better environmental stability than silver or
aluminium covered lines, but this also greatly depends on their chemical environment.
The impact of encapsulation on CIGS (mini) modules was only scarcely studied in this
thesis, but it was often observed that modules with the widely used encapsulant EVA
often underperformed compared to alternatives. This might be caused by acetic acid
formation.
CIGS degradation modes
Generally, the investigation of degradation processes in devices is complex and the
definite identification of failure mechanisms can be complicated due to the stacking
of multiple functional layers and thus the presence of multiple interfaces. However,
changes in the IV parameters are simple to assess and serve as an indication how a
solar cell degraded. Therefore, some factors are listed that influence the electrical
parameters V , J and fill factor and, altogether, determine the cell efficiency. These
oc
sc
factors should thus be kept in mind while trying to identify failures after accelerated
lifetime tests focused on terrestrial applications:
Changes in open circuit voltage:
o Absorber properties
Doping
Impurities
Bulk defects (increased recombination)
Grain boundaries
o pn-junction properties
Interface defects (increased recombination)
Changes in short circuit current
o Changes in the transparency of TCO
o Changes in SCR width (related to bulk properties of the absorber)
o Collection of generated charge carriers
o Contact corrosion
Delamination
262
The impact of two methods to make CIGS modules, showed that both methods have
their vulnerabilities: In monolithically integrated modules, the molybdenum and
the zinc oxide present in especially P2 and also in P3 in were shown to be unstable,
leading to increased series resistance. When grid connected modules are considered,
it seemed that nickel covered grids have a better environmental stability than silver or
aluminium covered lines, but this also greatly depends on their chemical environment.
The impact of encapsulation on CIGS (mini) modules was only scarcely studied in this
thesis, but it was often observed that modules with the widely used encapsulant EVA
often underperformed compared to alternatives. This might be caused by acetic acid
formation.
CIGS degradation modes
Generally, the investigation of degradation processes in devices is complex and the
definite identification of failure mechanisms can be complicated due to the stacking
of multiple functional layers and thus the presence of multiple interfaces. However,
changes in the IV parameters are simple to assess and serve as an indication how a
solar cell degraded. Therefore, some factors are listed that influence the electrical
parameters V , J and fill factor and, altogether, determine the cell efficiency. These
oc
sc
factors should thus be kept in mind while trying to identify failures after accelerated
lifetime tests focused on terrestrial applications:
Changes in open circuit voltage:
o Absorber properties
Doping
Impurities
Bulk defects (increased recombination)
Grain boundaries
o pn-junction properties
Interface defects (increased recombination)
Changes in short circuit current
o Changes in the transparency of TCO
o Changes in SCR width (related to bulk properties of the absorber)
o Collection of generated charge carriers
o Contact corrosion
Delamination
262
