Page 160 - Mirjam-Theelen-Degradation-of-CIGS-solar-cells

Chapter 5

When the selenium signals were considered (Figure 5.26), it was concluded that the
signal for the dense Mo25/2 is significantly higher than the for Mo25/15 signal. This
indicated that the oxidation seems to be more effective for the porous Mo25/15 than
for the dense Mo25/2. This difference can be explained by the morphology difference
of the two layers.
14
Se 3d Mo15 - degraded
12
10 3 counts/sec 10 8 Mo2 - degraded

6
4
2 Mo2 - non-
degraded
0
58 56 54 52 50
Figure 5.26 Binding energy (eV)
XPS spectra of selenium (Se 3d) signals for the non-degraded Mo25/2 and Mo25/2 and Mo25/15 after 150 hours of
o
exposure to 85C/85% RH.
More information about the oxidation process can be obtained in the Mo 3d-Se 3s XPS
profiles (Figure 5.27 and Table 5.9 ). For the non-degraded dense Mo25/2, the obtained
doublet can be resolved with a Mo 3d binding energy which is characteristic for
5/2
MoSe [27-29] and a 3.14 eV spin-orbit splitting. After degradation, the signal undergoes
2
a marked evolution: these new spectra have been fitted with the Line Shape signals of
45 Mo 6+
40 Mo 6+ MoSe 2
10 3 counts/sec 35 Mo 6+ Mo 5+ Mo 6+ Mo 5+ Mo15 - degraded
30
MoSe 2
25
20 Mo 5+ Mo 5+ Mo2 - degraded
15 MoSe 2
10
5 Mo2 - non-degraded
0
240 235 230 225 220
Figure 5.27 Binding energy (eV)
XPS spectra for the overlapping Mo 3d and Se 3s signals for the non-degraded Mo25/2 and Mo25/2 and Mo25/15 after 150
o
hours of exposure to 85 C/85% RH.

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