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Degradation mechanisms of the aluminium doped zinc oxide front contact
2
a power density of 1.61 W/cm . The deposition time was 50 minutes for both samples.
The samples varied in deposition temperature: one sample was not intentionally
heated as is mostly observed for CIGS cells (labeled ‘RT’, this sample heated slightly due
o
to the sputtering process, the highest reached temperature was 49C) while another
o
samples were heated to 200 C (labeled sample ‘200 C’), hereby reaching the maximal
o
temperature acceptable for deposition on top of a CIGS/CdS stack (see chapter 2.3.4).
These samples allowed us to look at a broad possible deposition spectrum, so the
optimal conditions can be selected for further CIGS production.
6.2.1.2 Atmospheric species treatment
ZnO:Al layers were deposited by radio frequency (RF) magnetron sputtering using a
MRC 643 vertical batch sputtering tool. The layers were sputtered on a 10x10 cm 0.7
2
mm thick Eagle 2000 Corning glass substrate from a rectangular 5"x17" high purity
ZnO ceramic target with 2% AlO . The flow of pure Ar gas was set to 15 sccm. The
3
2
chamber pressure was 0.42 Pa, while the RF power was 800 W, which corresponds to a
2
power density of 1.46 W/cm . The deposition time was 35 minutes and was executed
in 14 passes. The deposition was executed at room temperature.
6.2.2 Sample degradation
6.2.2.1 Damp heat treatment
The samples were submitted to a damp heat test, according to certification standard
IEC 61646, which describes 1000 hours exposure to damp heat (85C and 85% RH).
o
The damp heat test was performed in a temperature and humidity controlled
chamber (Espec Humidity Cabinet LHU-212). The samples were kept up to 2876
o
hours at 85 C/85% RH. Of both types, four individual samples have been degraded
and analyzed. The reported results are representative for the results of various other
similar experiments. The samples were characterised by different analysis techniques
before, during and after the degradation test (see section 6.2.3). Unless mentioned
otherwise, the measurements on degraded samples in this article are taken after
the damp heat treatment. When the samples were not in the climate chamber or
measured, they were stored in an inert atmosphere or wrapped in a container that
was evacuated to low pressure. A small number of samples were kept in the climate
chamber for 1000 hours with only a few interruptions. These were used as reference
samples to exclude the effect of continuous removal from the setup.
6.2.2.2 Atmospheric species treatment
All samples in this study were obtained from one 10x10 cm substrate with a ZnO:Al
2
coating, which was cut into smaller samples. The initial thickness and sheet resistance
179
2
a power density of 1.61 W/cm . The deposition time was 50 minutes for both samples.
The samples varied in deposition temperature: one sample was not intentionally
heated as is mostly observed for CIGS cells (labeled ‘RT’, this sample heated slightly due
o
to the sputtering process, the highest reached temperature was 49C) while another
o
samples were heated to 200 C (labeled sample ‘200 C’), hereby reaching the maximal
o
temperature acceptable for deposition on top of a CIGS/CdS stack (see chapter 2.3.4).
These samples allowed us to look at a broad possible deposition spectrum, so the
optimal conditions can be selected for further CIGS production.
6.2.1.2 Atmospheric species treatment
ZnO:Al layers were deposited by radio frequency (RF) magnetron sputtering using a
MRC 643 vertical batch sputtering tool. The layers were sputtered on a 10x10 cm 0.7
2
mm thick Eagle 2000 Corning glass substrate from a rectangular 5"x17" high purity
ZnO ceramic target with 2% AlO . The flow of pure Ar gas was set to 15 sccm. The
3
2
chamber pressure was 0.42 Pa, while the RF power was 800 W, which corresponds to a
2
power density of 1.46 W/cm . The deposition time was 35 minutes and was executed
in 14 passes. The deposition was executed at room temperature.
6.2.2 Sample degradation
6.2.2.1 Damp heat treatment
The samples were submitted to a damp heat test, according to certification standard
IEC 61646, which describes 1000 hours exposure to damp heat (85C and 85% RH).
o
The damp heat test was performed in a temperature and humidity controlled
chamber (Espec Humidity Cabinet LHU-212). The samples were kept up to 2876
o
hours at 85 C/85% RH. Of both types, four individual samples have been degraded
and analyzed. The reported results are representative for the results of various other
similar experiments. The samples were characterised by different analysis techniques
before, during and after the degradation test (see section 6.2.3). Unless mentioned
otherwise, the measurements on degraded samples in this article are taken after
the damp heat treatment. When the samples were not in the climate chamber or
measured, they were stored in an inert atmosphere or wrapped in a container that
was evacuated to low pressure. A small number of samples were kept in the climate
chamber for 1000 hours with only a few interruptions. These were used as reference
samples to exclude the effect of continuous removal from the setup.
6.2.2.2 Atmospheric species treatment
All samples in this study were obtained from one 10x10 cm substrate with a ZnO:Al
2
coating, which was cut into smaller samples. The initial thickness and sheet resistance
179
