Page 53 - Mirjam-Theelen-Degradation-of-CIGS-solar-cells
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Stability of Cu(In,Ga)Se 2 Solar Cells
also more stable during damp heat exposure. It should be noticed that the included
data are taken from the literature studied in this work, but might not give a complete
picture, since many reports about a certain material (e.g. i-ZnO/ZnO:Al) come from
one dominant source, while other sources might show different degradation rates for
the resistivity. It can therefore also not be concluded that a significant difference in
degradation behaviour between ZnO:Al and the combined i-ZnO/ZnO:Al stack exists.
However, it is clear that ITO is more stable and far more predictable than the zinc
oxide based stacks. These stacks show degradation rate of the resistivity varying over
more than five orders of magnitudes.
Additionally, in the supplementary information, a table shows a literature overview of
the degradation rates of the resistivity (ρ), Hall mobility (µ ) and carrier concentra-
Hall
tion (n Hall ) under different degradation conditions. A wide range of TCOs (type, layer
thickness and deposition technique) for CIGS cells are included.
Based on this information and on the information of Pern et al. [59], that is based on
the electrical, optical, structural and morphological analysis of various types of TCOs,
the order of degradation rates for TCO materials is
ZnO >> IZO > ITO > FTO
This indicates zinc oxide has the highest and fluorine-doped tin oxide the lowest deg -
radation rate.
It should be noted that tin oxide as well as indium zinc oxide are not further described
in this chapter, since only few studies using these TCOs in high efficiency CIGS solar
cells exist. Nevertheless, the impact of the stability of SnO in a CIGS solar cell is de-
2
scribed in chapter 2.3.4.3 [60,61].
2.3.4.1 Zinc oxide degradation
2.3.4.1.1 General degradation mechanisms
Zinc oxide based materials are in general non-toxic, inexpensive and abundant and
therefore often chosen as a TCO in CIGS samples. In general, the samples are deposit-
o
ed by sputtering without additional heating or at least below 200 C to prevent dam-
age to the underlying layers.
Studies by Greiner [62,63], Ando [64-66], Minami [67,68], Zhan [69], Tohsophon [70],
Theelen [71], Hüpkes [72], Pern [19,24,25,30,44,59,73], Sundaramoorthy [74], Feist [29]
Lin [75], Owen [76], Hamasha [77], Kim [78], Steinhauser [79], Illiberi [80] and their
coworkers have focused on ‘damp heat’ degradation of doped ZnO. Additionally, an
interesting overview about degradation of zinc oxide for CIGS was written by Klenk
[81]. In all these publications, the focus often lies on sputtered aluminium doped zinc
51
also more stable during damp heat exposure. It should be noticed that the included
data are taken from the literature studied in this work, but might not give a complete
picture, since many reports about a certain material (e.g. i-ZnO/ZnO:Al) come from
one dominant source, while other sources might show different degradation rates for
the resistivity. It can therefore also not be concluded that a significant difference in
degradation behaviour between ZnO:Al and the combined i-ZnO/ZnO:Al stack exists.
However, it is clear that ITO is more stable and far more predictable than the zinc
oxide based stacks. These stacks show degradation rate of the resistivity varying over
more than five orders of magnitudes.
Additionally, in the supplementary information, a table shows a literature overview of
the degradation rates of the resistivity (ρ), Hall mobility (µ ) and carrier concentra-
Hall
tion (n Hall ) under different degradation conditions. A wide range of TCOs (type, layer
thickness and deposition technique) for CIGS cells are included.
Based on this information and on the information of Pern et al. [59], that is based on
the electrical, optical, structural and morphological analysis of various types of TCOs,
the order of degradation rates for TCO materials is
ZnO >> IZO > ITO > FTO
This indicates zinc oxide has the highest and fluorine-doped tin oxide the lowest deg -
radation rate.
It should be noted that tin oxide as well as indium zinc oxide are not further described
in this chapter, since only few studies using these TCOs in high efficiency CIGS solar
cells exist. Nevertheless, the impact of the stability of SnO in a CIGS solar cell is de-
2
scribed in chapter 2.3.4.3 [60,61].
2.3.4.1 Zinc oxide degradation
2.3.4.1.1 General degradation mechanisms
Zinc oxide based materials are in general non-toxic, inexpensive and abundant and
therefore often chosen as a TCO in CIGS samples. In general, the samples are deposit-
o
ed by sputtering without additional heating or at least below 200 C to prevent dam-
age to the underlying layers.
Studies by Greiner [62,63], Ando [64-66], Minami [67,68], Zhan [69], Tohsophon [70],
Theelen [71], Hüpkes [72], Pern [19,24,25,30,44,59,73], Sundaramoorthy [74], Feist [29]
Lin [75], Owen [76], Hamasha [77], Kim [78], Steinhauser [79], Illiberi [80] and their
coworkers have focused on ‘damp heat’ degradation of doped ZnO. Additionally, an
interesting overview about degradation of zinc oxide for CIGS was written by Klenk
[81]. In all these publications, the focus often lies on sputtered aluminium doped zinc
51
