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The impact of alkali elements
Figure 7.7
Short circuit current density of the alkali-rich and alkali-poor samples as determined by EQE and from the IV measurements
as obtained in the hybrid setup.
Figure 7.5: Short circuit current density of the alkali rich and alkali poor samples as determined by EQE and
from the IV measurements as btained in the hybrid setup.
observed by Ramanathan et al. [11], who observed this due to two minutes annealing
at 250 C of CIGS solar cell containing a CdS layer. The reasons for this change are still
o
unclear, but various suggestions were given: they proposed that a reaction between
i-ZnO and CdS occurred, resulting in the formation of an intermediate material with a
high bandgap. Suggested candidates are Cd Zn S and ZnO S , but no evidence of
1-x
x
1-x x
these new species have been found in this study.
The short circuit current density as measured by both EQE and IV was also compared
(Figure 7.7). In this study, these measurements show good similarity for the alkali-poor
samples, while the alkali-rich samples can show deviations of up to 3.4 mA/cm. In
2
earlier studies, this difference could be as large as 12 mA/cm or 41% of the highest
2
value. In these cases, the EQE values were always higher than the IV values, while in
this experiment, the general trend is in the opposite direction. These difference might
have been caused by differences in light intensity between IV and EQE, but this theory
has not been validated yet.
7.3.4 Development of temperature dependent IV
The temperature dependent current voltage curves (IV(T)) were measured in order to
study the defects in the samples. Figure 7.8 and 7.9 show the IV curves as a function
of temperature under illumination before degradation and after 165 hours exposure
under illumination and in darkness respectively. It was observed that all non-degraded
samples, both in light and darkness show losses which cannot be explained as simple
series resistance. The alkali-rich sample under illumination also showed a kink at lower
temperatures, indicating recombination for majority carriers under forward bias. This
difference in electronic transport occurred at temperatures below ~190K, but did not
223
Figure 7.7
Short circuit current density of the alkali-rich and alkali-poor samples as determined by EQE and from the IV measurements
as obtained in the hybrid setup.
Figure 7.5: Short circuit current density of the alkali rich and alkali poor samples as determined by EQE and
from the IV measurements as btained in the hybrid setup.
observed by Ramanathan et al. [11], who observed this due to two minutes annealing
at 250 C of CIGS solar cell containing a CdS layer. The reasons for this change are still
o
unclear, but various suggestions were given: they proposed that a reaction between
i-ZnO and CdS occurred, resulting in the formation of an intermediate material with a
high bandgap. Suggested candidates are Cd Zn S and ZnO S , but no evidence of
1-x
x
1-x x
these new species have been found in this study.
The short circuit current density as measured by both EQE and IV was also compared
(Figure 7.7). In this study, these measurements show good similarity for the alkali-poor
samples, while the alkali-rich samples can show deviations of up to 3.4 mA/cm. In
2
earlier studies, this difference could be as large as 12 mA/cm or 41% of the highest
2
value. In these cases, the EQE values were always higher than the IV values, while in
this experiment, the general trend is in the opposite direction. These difference might
have been caused by differences in light intensity between IV and EQE, but this theory
has not been validated yet.
7.3.4 Development of temperature dependent IV
The temperature dependent current voltage curves (IV(T)) were measured in order to
study the defects in the samples. Figure 7.8 and 7.9 show the IV curves as a function
of temperature under illumination before degradation and after 165 hours exposure
under illumination and in darkness respectively. It was observed that all non-degraded
samples, both in light and darkness show losses which cannot be explained as simple
series resistance. The alkali-rich sample under illumination also showed a kink at lower
temperatures, indicating recombination for majority carriers under forward bias. This
difference in electronic transport occurred at temperatures below ~190K, but did not
223
