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The impact of atmospheric species
8.1 Introduction
The requirements of flexible barriers and encapsulation for CIGS solar cells are
normally only based on water penetration numbers, and in some cases on oxygen
penetration, while it is not clear which atmospheric gases are actually involved in the
degradation of CIGS solar cells. Since it is known that increased resistance of ZnO:Al is
often a reason for CIGS solar cell degradation, in chapter 6, it was shown that ZnO:Al
layers undergo a large performance deterioration due to combined water and CO
2
exposure, while these layers were stable under many other conditions.
Based on earlier experiments, it could be expected that CO is important [1,2,3], but
2
this has not been studied yet. Therefore, the impact on complete CIGS solar cells was
unknown, but it could be expected that the combined impact of water and CO will be
2
detrimental for the ZnO:Al layer of the solar cells, while other layers might be affected
by different combinations. Therefore, we have studied the impact of the exposure
of CIGS solar cells to water combined with atmospheric gases (air, N, O and CO ) in
2
2
2
order to learn more about the influence of these species and their combination on the
degradation.
8.2 Experimental
8.2.1 Sample preparation
Eight similar solar cells as introduced in chapter 3.2 with a width of 6.9±0.4 mm and a
length of 4.3±0.1 mm length were cut from one microscopy slide. The total cell area
was therefore 30±2 mm .
2
Figure 8.1a and b depict the schematic cross-section and top view of the solar cells
(a) (b) (c)
Figure 8.1
Samples as used in the experiments: (a) Schematic cross-section (b) Schematic top view (c) Photograph of the top view.
241
8.1 Introduction
The requirements of flexible barriers and encapsulation for CIGS solar cells are
normally only based on water penetration numbers, and in some cases on oxygen
penetration, while it is not clear which atmospheric gases are actually involved in the
degradation of CIGS solar cells. Since it is known that increased resistance of ZnO:Al is
often a reason for CIGS solar cell degradation, in chapter 6, it was shown that ZnO:Al
layers undergo a large performance deterioration due to combined water and CO
2
exposure, while these layers were stable under many other conditions.
Based on earlier experiments, it could be expected that CO is important [1,2,3], but
2
this has not been studied yet. Therefore, the impact on complete CIGS solar cells was
unknown, but it could be expected that the combined impact of water and CO will be
2
detrimental for the ZnO:Al layer of the solar cells, while other layers might be affected
by different combinations. Therefore, we have studied the impact of the exposure
of CIGS solar cells to water combined with atmospheric gases (air, N, O and CO ) in
2
2
2
order to learn more about the influence of these species and their combination on the
degradation.
8.2 Experimental
8.2.1 Sample preparation
Eight similar solar cells as introduced in chapter 3.2 with a width of 6.9±0.4 mm and a
length of 4.3±0.1 mm length were cut from one microscopy slide. The total cell area
was therefore 30±2 mm .
2
Figure 8.1a and b depict the schematic cross-section and top view of the solar cells
(a) (b) (c)
Figure 8.1
Samples as used in the experiments: (a) Schematic cross-section (b) Schematic top view (c) Photograph of the top view.
241
