Page 204 - Mirjam-Theelen-Degradation-of-CIGS-solar-cells
P. 204
Chapter 6
+
2+
ZnO (s) + 2H (aq) → Zn (aq) + H O(l) (chemical dissolution) (6.2)
2
Another route to the dissolution of zinc oxide is due to the impact of light under some
conditions:
2 ZnO (s) + 4hν → 2Zn (aq) + O (g) + 4e [21] (6.3)
2+
-
2
After formation, this Zn can either wash away with the water or react into other
2+
species. In this case, the layers keep the same structural characteristics, so it is not
2+
likely that Zn has disappeared from the samples.
More information about the nature of the species formed in the grain boundaries
was found in literature and by calculations. The first hint for possible stable reaction
products of zinc oxide degradation can be found in nature. In exposed deposits, most
of the mined zinc compounds are sulphides, carbonates and hydrocarbonates.
The reaction products of zinc compounds in nature were already described in
literature [20]. This shows the large amount of reaction products that occur in nature,
and the possibility that multiple corrosion products can be present at the same place.
Although aluminium doped zinc oxide is naturally a different material then pure zinc,
it can be assumed that various of the reaction products should be similar for ZnO:Al.
The corrosion products of zinc in the presence of only carbon, oxygen and hydrogen
are ZnO, Zn(OH) , ZnCO , Zn (CO ) (OH) and Zn CO (OH) •H O. In addition to these pre -
6
2
3
6
4
5
3
2
3 2
dominantly found oxides, hydroxides and carbonates, various sulphur or chloride ba-
sed compounds were also detected. These products include Zn SO (OH) •nH O (basic
4
6
2
4
zinc sulphate), ZnCl (OH) SO •5H O (zinc chlorohydroxysulphate), (Zn,Cu)SO 4
2
4
4
4
2
4
(OH) •4H O, NaZnCl(OH) SO •6H O, Zn (OH) Cl •H O (zinc hydroxychloride), ZnSO
8
2
5
2
4
6
2
2
4
4
6
and ZnSO •nH O (zinc sulphate). This indicates that sulphur and chloride based reacti -
4
2
on products also occur in nature.
In nature, the relative amount of chlorine in the corrosion products is usually low due
to the high solubility of the chloride containing compounds. However, while in the
nature rain is omnipresent, no large quantities of liquid water have been in contact
with our samples in this damp heat experiment, so these molecules can still be present
in this case. Therefore, chlorine species might be found less in CIGS panels in the field,
but might still play an important role in their degradation.
It was also found that the corrosion products are often not uniform with depth.
ZnO was found in the outer 15 nm of the surface layer, while Zn(OH) or ZnCO were
3
2
found deeper in the film. Chlorine and sulphur based species were present as surface
202
+
2+
ZnO (s) + 2H (aq) → Zn (aq) + H O(l) (chemical dissolution) (6.2)
2
Another route to the dissolution of zinc oxide is due to the impact of light under some
conditions:
2 ZnO (s) + 4hν → 2Zn (aq) + O (g) + 4e [21] (6.3)
2+
-
2
After formation, this Zn can either wash away with the water or react into other
2+
species. In this case, the layers keep the same structural characteristics, so it is not
2+
likely that Zn has disappeared from the samples.
More information about the nature of the species formed in the grain boundaries
was found in literature and by calculations. The first hint for possible stable reaction
products of zinc oxide degradation can be found in nature. In exposed deposits, most
of the mined zinc compounds are sulphides, carbonates and hydrocarbonates.
The reaction products of zinc compounds in nature were already described in
literature [20]. This shows the large amount of reaction products that occur in nature,
and the possibility that multiple corrosion products can be present at the same place.
Although aluminium doped zinc oxide is naturally a different material then pure zinc,
it can be assumed that various of the reaction products should be similar for ZnO:Al.
The corrosion products of zinc in the presence of only carbon, oxygen and hydrogen
are ZnO, Zn(OH) , ZnCO , Zn (CO ) (OH) and Zn CO (OH) •H O. In addition to these pre -
6
2
3
6
4
5
3
2
3 2
dominantly found oxides, hydroxides and carbonates, various sulphur or chloride ba-
sed compounds were also detected. These products include Zn SO (OH) •nH O (basic
4
6
2
4
zinc sulphate), ZnCl (OH) SO •5H O (zinc chlorohydroxysulphate), (Zn,Cu)SO 4
2
4
4
4
2
4
(OH) •4H O, NaZnCl(OH) SO •6H O, Zn (OH) Cl •H O (zinc hydroxychloride), ZnSO
8
2
5
2
4
6
2
2
4
4
6
and ZnSO •nH O (zinc sulphate). This indicates that sulphur and chloride based reacti -
4
2
on products also occur in nature.
In nature, the relative amount of chlorine in the corrosion products is usually low due
to the high solubility of the chloride containing compounds. However, while in the
nature rain is omnipresent, no large quantities of liquid water have been in contact
with our samples in this damp heat experiment, so these molecules can still be present
in this case. Therefore, chlorine species might be found less in CIGS panels in the field,
but might still play an important role in their degradation.
It was also found that the corrosion products are often not uniform with depth.
ZnO was found in the outer 15 nm of the surface layer, while Zn(OH) or ZnCO were
3
2
found deeper in the film. Chlorine and sulphur based species were present as surface
202
