Page 271 - Mirjam-Theelen-Degradation-of-CIGS-solar-cells
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Summaries - Summary
2. ‘Hybrid degradation’ test (https://www.youtube.com/watch?v=Zmy5tb-
2NK8) – a combination of damp heat exposure and AM 1.5 illumination. This
allows simultaneous sample degradation with elevated temperature and
humidity as well as illumination as loads, while the samples can also be in-
situ monitored, in order to learn more about the degradation behaviour. This
setup has been designed and built within this study and attracted interest
from external parties. Therefore, a consortium of three Dutch SMEs (Eternal
Sun, Hielkema Testequipment and ReRa Solutions) is currently working on the
commercialisation of this setup.
3. ‘Atmospheric species’ exposure – the cells and layers have been exposed
to individual species occurring in air, like oxygen, nitrogen, carbon dioxide
and water, and combination of these species. This helps the identification of
the species that are responsible for the degradation of CIGS solar cells. This
can lead to the identification of the degradation mechanisms and can allow
optimisation of cost-effective and effective barrier materials. This setup has
been designed and built as part of this study.
Barrier materials are not used in any of these tests in order to even further accelerate
the degradation rate.
These tests, combined with extensive analysis of samples with among others IV, EQE,
IV(T), EL, PL, lock-in thermography, 4PP, Hall, UV-VIS-NIR, Raman, XRD, SEM-EDX, HIM
and SIMS, have led to the following conclusion on the degradation of CIGS solar cells
and its constituents:
Molybdenum back contact
The molybdenum back contact has been degraded under conditions 1 and 3.
Molybdenum degraded very quickly in the combined presence of water and oxygen,
while it is reasonably stable in the absence of either of these species.
It was observed that molybdenum degrades due to the formation of molybdenum
oxides. This layer, which often forms at the surface of the molybdenum, is largely
non-conductive and has a low reflectivity. The appearance of this top oxide layer,
can therefore lead to a sudden disappearance of the conductivity, when measured
on the surface. This layer consist of MoO mixed with MoO ,which forms due to the
2.5
3
intercalation of Na into a MoO matrix. This is possible due to the layered structure of
+
3
MoO and leads to the partial reduction of Mo to Mo . This can lead to the formation
5+
6+
3
of a more conductive degradation product.
Furthermore, it was observed that more porous molybdenum, deposited at higher
deposition pressures, is more vulnerable to damp heat exposure than more dense
material, while the formation of a top layer MoSe , which is also present in a CIGS solar
2
269
2. ‘Hybrid degradation’ test (https://www.youtube.com/watch?v=Zmy5tb-
2NK8) – a combination of damp heat exposure and AM 1.5 illumination. This
allows simultaneous sample degradation with elevated temperature and
humidity as well as illumination as loads, while the samples can also be in-
situ monitored, in order to learn more about the degradation behaviour. This
setup has been designed and built within this study and attracted interest
from external parties. Therefore, a consortium of three Dutch SMEs (Eternal
Sun, Hielkema Testequipment and ReRa Solutions) is currently working on the
commercialisation of this setup.
3. ‘Atmospheric species’ exposure – the cells and layers have been exposed
to individual species occurring in air, like oxygen, nitrogen, carbon dioxide
and water, and combination of these species. This helps the identification of
the species that are responsible for the degradation of CIGS solar cells. This
can lead to the identification of the degradation mechanisms and can allow
optimisation of cost-effective and effective barrier materials. This setup has
been designed and built as part of this study.
Barrier materials are not used in any of these tests in order to even further accelerate
the degradation rate.
These tests, combined with extensive analysis of samples with among others IV, EQE,
IV(T), EL, PL, lock-in thermography, 4PP, Hall, UV-VIS-NIR, Raman, XRD, SEM-EDX, HIM
and SIMS, have led to the following conclusion on the degradation of CIGS solar cells
and its constituents:
Molybdenum back contact
The molybdenum back contact has been degraded under conditions 1 and 3.
Molybdenum degraded very quickly in the combined presence of water and oxygen,
while it is reasonably stable in the absence of either of these species.
It was observed that molybdenum degrades due to the formation of molybdenum
oxides. This layer, which often forms at the surface of the molybdenum, is largely
non-conductive and has a low reflectivity. The appearance of this top oxide layer,
can therefore lead to a sudden disappearance of the conductivity, when measured
on the surface. This layer consist of MoO mixed with MoO ,which forms due to the
2.5
3
intercalation of Na into a MoO matrix. This is possible due to the layered structure of
+
3
MoO and leads to the partial reduction of Mo to Mo . This can lead to the formation
5+
6+
3
of a more conductive degradation product.
Furthermore, it was observed that more porous molybdenum, deposited at higher
deposition pressures, is more vulnerable to damp heat exposure than more dense
material, while the formation of a top layer MoSe , which is also present in a CIGS solar
2
269
