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P. 150
Chapter 5
non-selenised samples (Mo10 and Mo15). However, this figure also shows that many
data points are not depicted for Mo10Se, Mo15 and Mo15Se, indicating that the layer
had become non-conductive. This already started after 13 hours and is explained by
the formation of an isolating MoO layer which separates the conductive molybdenum
x
from the measurement pins. This layer slowly covers the complete surface. Here, the
impact of the sputtering pressure was observed. The porous samples (Mo15, Mo10Se,
Mo15Se) had already largely lost their conductivity after 41 hours at 85 C and 85% RH,
o
while the more dense samples still showed conductivity after 105 hours.
5.3.1.8 Changes in reflectance
Before and after each degradation step, the reflectance of the samples was measured
with a UV-VIS spectrophotometer, as depicted in Figure 5.15. A wavelength range of
300 to 1200 nm is depicted, since most CIGS absorbers absorb in this range. The CIGS
solar cells described in this thesis generally show absorption between approximately
340 and 1150 nm. Before degradation, there is a clear trend visible: the samples with
a higher argon sputter pressure had a lower reflectance in this wavelength range.
Next to that, the selenised samples have a lower reflectance than the non-selenised
samples. Therefore, the sample with the lowest argon sputter pressure without
selenisation has the highest initial reflectance.
After 57 hours of degradation, not shown here, the reflectance of Mo10Se, Mo10 and
Mo15 has decreased to around 10%. Mo2 and Mo15Se vary between the 10% and 30%
(a) 60 (b) 60
Before degradation After 105 hours exposure
50 50
40 40
Reflectance (%) 30 Reflectance (%) 30
20 Mo2 20
Mo10
Mo15
10 Mo2Se 10
Mo10Se
Mo15Se
0 0
400 600 800 1000 1200 400 600 800 1000 1200
Wavelength (nm) Wavelength (nm)
Figure 5.15
Reflectance of the samples plotted against the wavelength of the incident light before and after 105 hours exposure to
o
85 C/85% RH.
148
non-selenised samples (Mo10 and Mo15). However, this figure also shows that many
data points are not depicted for Mo10Se, Mo15 and Mo15Se, indicating that the layer
had become non-conductive. This already started after 13 hours and is explained by
the formation of an isolating MoO layer which separates the conductive molybdenum
x
from the measurement pins. This layer slowly covers the complete surface. Here, the
impact of the sputtering pressure was observed. The porous samples (Mo15, Mo10Se,
Mo15Se) had already largely lost their conductivity after 41 hours at 85 C and 85% RH,
o
while the more dense samples still showed conductivity after 105 hours.
5.3.1.8 Changes in reflectance
Before and after each degradation step, the reflectance of the samples was measured
with a UV-VIS spectrophotometer, as depicted in Figure 5.15. A wavelength range of
300 to 1200 nm is depicted, since most CIGS absorbers absorb in this range. The CIGS
solar cells described in this thesis generally show absorption between approximately
340 and 1150 nm. Before degradation, there is a clear trend visible: the samples with
a higher argon sputter pressure had a lower reflectance in this wavelength range.
Next to that, the selenised samples have a lower reflectance than the non-selenised
samples. Therefore, the sample with the lowest argon sputter pressure without
selenisation has the highest initial reflectance.
After 57 hours of degradation, not shown here, the reflectance of Mo10Se, Mo10 and
Mo15 has decreased to around 10%. Mo2 and Mo15Se vary between the 10% and 30%
(a) 60 (b) 60
Before degradation After 105 hours exposure
50 50
40 40
Reflectance (%) 30 Reflectance (%) 30
20 Mo2 20
Mo10
Mo15
10 Mo2Se 10
Mo10Se
Mo15Se
0 0
400 600 800 1000 1200 400 600 800 1000 1200
Wavelength (nm) Wavelength (nm)
Figure 5.15
Reflectance of the samples plotted against the wavelength of the incident light before and after 105 hours exposure to
o
85 C/85% RH.
148
