Page 190 - Mirjam-Theelen-Degradation-of-CIGS-solar-cells
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Chapter 6
Within the highly transparent region, the measured spectra show an oscillatory
behaviour that is caused by interference effects due to multiple internal reflections
of the incoming light in the zinc oxide layer. The degradation has not influenced this
behaviour, so no texturing or reduction of zinc oxide to zinc has occurred.
6.3.1.4 Electrical properties
The electrical properties were determined by Hall Van der Pauw and four point probe
measurements. Both films exhibited an n-type behaviour, which is in conformity with
the type of conduction mechanism associated with these ZnO:Al semiconductors.
Figure 6.8 depicts the development of resistivity of the two samples with degradation
time as obtained by Hall measurements. The resistivity data obtained by the four point
probe have the same shape with a small offset and are not shown. It was observed
that the 200C sample has an initial resistivity of 6x10Ωcm, which is a factor two
-4
o
o
lower than the RT sample. After exposure to 85C/85% RH, the detoriation was also
faster for the RT sample. The RT sample is therefore more vulnerable to damp heat.
2,5x10 -3
RT
2,0x10 -3
Resistivity ( cm) 1,5x10 -3
o
1,0x10 -3 200 C
5,0x10 -4
0 500 1000 1500 2000 2500 3000
o
Figure 6.8 Time at 85 C/85% RH (hours)
o
Resistivity of the RT (red) and 200 C(blue) ZnO:Al samples as a function of time at 85 C/85% RH.
o
This is a different conclusion than drawn in reference [4], in which no influence of
sputtering temperature in a similar deposition temperature range was reported.
However, in that case, samples obtained with a different deposition technique (Pulsed
Laser Deposition) and a different thickness range (20-200 nm) were studied.
The increase in resistivity of both samples can be fitted with a square root function,
following:
y = a * √(bt) + c (6.1)
188
Within the highly transparent region, the measured spectra show an oscillatory
behaviour that is caused by interference effects due to multiple internal reflections
of the incoming light in the zinc oxide layer. The degradation has not influenced this
behaviour, so no texturing or reduction of zinc oxide to zinc has occurred.
6.3.1.4 Electrical properties
The electrical properties were determined by Hall Van der Pauw and four point probe
measurements. Both films exhibited an n-type behaviour, which is in conformity with
the type of conduction mechanism associated with these ZnO:Al semiconductors.
Figure 6.8 depicts the development of resistivity of the two samples with degradation
time as obtained by Hall measurements. The resistivity data obtained by the four point
probe have the same shape with a small offset and are not shown. It was observed
that the 200C sample has an initial resistivity of 6x10Ωcm, which is a factor two
-4
o
o
lower than the RT sample. After exposure to 85C/85% RH, the detoriation was also
faster for the RT sample. The RT sample is therefore more vulnerable to damp heat.
2,5x10 -3
RT
2,0x10 -3
Resistivity ( cm) 1,5x10 -3
o
1,0x10 -3 200 C
5,0x10 -4
0 500 1000 1500 2000 2500 3000
o
Figure 6.8 Time at 85 C/85% RH (hours)
o
Resistivity of the RT (red) and 200 C(blue) ZnO:Al samples as a function of time at 85 C/85% RH.
o
This is a different conclusion than drawn in reference [4], in which no influence of
sputtering temperature in a similar deposition temperature range was reported.
However, in that case, samples obtained with a different deposition technique (Pulsed
Laser Deposition) and a different thickness range (20-200 nm) were studied.
The increase in resistivity of both samples can be fitted with a square root function,
following:
y = a * √(bt) + c (6.1)
188
