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Chapter 4
increase in photocurrent density and a relatively stable saturation current, instead
of the exponential growth presented by the SLG samples. For the PI samples, the
evolutions of n, J and J are all in favour of an increase of J when the temperature
sc
ph
o
increases, while the opposite is true for the SLG samples.
When the relationship between the temperature coefficients and the short circuit
current at room temperature, as is shown in Figures 4.4 and 4.5, are studied, no
relationship can be observed. It therefore seems that various factors influence the
current density at high temperature [20], but the room temperature values do not
have a strong impact on the temperature dependency.
4.4.3 Temperature dependency of the fill factor and resistances
In the past the temperature dependence of the series and shunt resistance was
only considered to have a minor impact on the efficiency change for increasing
temperature [19]. In this study, measurements have shown that there is a dependency
between these resistances and temperature. These changes impact on the fill factor
and thus on the overall efficiency of the cells.
When the series resistance is considered, an increase of the temperature led to a
slight decrease of the series resistance, which should lead to a small improvement
the fill factor of the cells. If the series resistance of most cells is studied in more detail,
it is visible that they generally do not decrease linearly, but via multiple stages, which
can for example be better fitted with a quadratic function. It is proposed that multiple
factors are playing a role its temperature dependency, which are all dominant at other
temperatures. In general, the impact of the series resistance change on the efficiency is
probably relatively small. It was also observed that the shunt resistance R sh\ is decreasing
rapidly with temperature.
Since the magnitude of the decrease of the shunt resistance as well as the open circuit
voltage decrease is a lot larger than the decrease of series resistance, the fill factor has
a clear negative trend with increasing temperature. One exception was observed for a
sample with a low fill factor, which actually had a positive shunt resistance trend. This
again shows that a large variation between the samples can exist. When the relationship
between the fill factor at room temperature and its temperature coefficients is studies
(Figure 4.4 and Figure 4.5), no clear trend can be obtained from these data points.
4.4.4 Temperature dependency of the efficiency
Since the open circuit voltage and fill factor decrease strongly with increasing
temperature, while the short circuit current density either decreases or increases
slightly, the efficiency decreases strongly with temperature. The temperature
coefficient of the efficiency as described in Table 4.2 and Table 4.3 show a wide range
120
increase in photocurrent density and a relatively stable saturation current, instead
of the exponential growth presented by the SLG samples. For the PI samples, the
evolutions of n, J and J are all in favour of an increase of J when the temperature
sc
ph
o
increases, while the opposite is true for the SLG samples.
When the relationship between the temperature coefficients and the short circuit
current at room temperature, as is shown in Figures 4.4 and 4.5, are studied, no
relationship can be observed. It therefore seems that various factors influence the
current density at high temperature [20], but the room temperature values do not
have a strong impact on the temperature dependency.
4.4.3 Temperature dependency of the fill factor and resistances
In the past the temperature dependence of the series and shunt resistance was
only considered to have a minor impact on the efficiency change for increasing
temperature [19]. In this study, measurements have shown that there is a dependency
between these resistances and temperature. These changes impact on the fill factor
and thus on the overall efficiency of the cells.
When the series resistance is considered, an increase of the temperature led to a
slight decrease of the series resistance, which should lead to a small improvement
the fill factor of the cells. If the series resistance of most cells is studied in more detail,
it is visible that they generally do not decrease linearly, but via multiple stages, which
can for example be better fitted with a quadratic function. It is proposed that multiple
factors are playing a role its temperature dependency, which are all dominant at other
temperatures. In general, the impact of the series resistance change on the efficiency is
probably relatively small. It was also observed that the shunt resistance R sh\ is decreasing
rapidly with temperature.
Since the magnitude of the decrease of the shunt resistance as well as the open circuit
voltage decrease is a lot larger than the decrease of series resistance, the fill factor has
a clear negative trend with increasing temperature. One exception was observed for a
sample with a low fill factor, which actually had a positive shunt resistance trend. This
again shows that a large variation between the samples can exist. When the relationship
between the fill factor at room temperature and its temperature coefficients is studies
(Figure 4.4 and Figure 4.5), no clear trend can be obtained from these data points.
4.4.4 Temperature dependency of the efficiency
Since the open circuit voltage and fill factor decrease strongly with increasing
temperature, while the short circuit current density either decreases or increases
slightly, the efficiency decreases strongly with temperature. The temperature
coefficient of the efficiency as described in Table 4.2 and Table 4.3 show a wide range
120
