9.1.3
9.1.4
In the ideal case, J sc is equal to J ph , which can easily be derived from Eq. (8.33). J ph
can be approximated by Eq. (8.34), which shows that in the case of an ideal diode (for
example no surface recombination) and uniform generation, the critical material
parameters that determine J ph are the diffusion lengths of minority carriers. Crystalline
silicon solar cells can deliver under an AM1.5 spectrum a maximum possible current
density of 46 mA/cm
2
. In laboratory c-Si solar cells the measured J sc is above 42 mA/cm
2 ,
while commercial solar cells have a J sc exceeding 35 mA/cm
2
.
Open circuit voltage
The open-circuit voltage is the voltage at which no current flows through the external
circuit. It is the maximum voltage that a solar cell can deliver. V oc corresponds to the
forward bias voltage, at which the dark current density compensates the photocurrent
density. V oc depends on the photo generated current density and can be calculated from Eq.
(8.33) assuming that the net current is zero,
where the approximation is justified because of J ph ≫ J 0
Equation (9.1) shows that V oc depends on the saturation current density of the solar
cell and the photo generated current. While J ph typically has a small variation, the key
effect is the saturation current, since this may vary by orders of magnitude. The saturation
current density, J 0 , depends on the recombination in the solar cell. Therefore, V oc is a
measure of the amount of recombination in the device. Laboratory crystalline silicon solar
cells have a V oc of up to 720 mV under the standard AM1.5 conditions, while commercial
solar cells typically have V oc exceeding 600 mV.
Fill factor
The fill factor is the ratio between the maximum power (P max = J mpp V mpp ) generated by a
solar cell and the product of V oc with J sc (see Figure 8.10),
The subscript “mpp” in Eq. (9.2) denotes the maximum power point (MPP) of the solar
cell, i.e. the point on the J-V characteristic of the solar cell, at which the solar cell has the
maximal power output. To optimize the operation of PV systems, it is very important, to
operate the solar cells (or PV modules) at the MPP. This is ensured with maximum power
9.1.4
In the ideal case, J sc is equal to J ph , which can easily be derived from Eq. (8.33). J ph
can be approximated by Eq. (8.34), which shows that in the case of an ideal diode (for
example no surface recombination) and uniform generation, the critical material
parameters that determine J ph are the diffusion lengths of minority carriers. Crystalline
silicon solar cells can deliver under an AM1.5 spectrum a maximum possible current
density of 46 mA/cm
2
. In laboratory c-Si solar cells the measured J sc is above 42 mA/cm
2 ,
while commercial solar cells have a J sc exceeding 35 mA/cm
2
.
Open circuit voltage
The open-circuit voltage is the voltage at which no current flows through the external
circuit. It is the maximum voltage that a solar cell can deliver. V oc corresponds to the
forward bias voltage, at which the dark current density compensates the photocurrent
density. V oc depends on the photo generated current density and can be calculated from Eq.
(8.33) assuming that the net current is zero,
where the approximation is justified because of J ph ≫ J 0
Equation (9.1) shows that V oc depends on the saturation current density of the solar
cell and the photo generated current. While J ph typically has a small variation, the key
effect is the saturation current, since this may vary by orders of magnitude. The saturation
current density, J 0 , depends on the recombination in the solar cell. Therefore, V oc is a
measure of the amount of recombination in the device. Laboratory crystalline silicon solar
cells have a V oc of up to 720 mV under the standard AM1.5 conditions, while commercial
solar cells typically have V oc exceeding 600 mV.
Fill factor
The fill factor is the ratio between the maximum power (P max = J mpp V mpp ) generated by a
solar cell and the product of V oc with J sc (see Figure 8.10),
The subscript “mpp” in Eq. (9.2) denotes the maximum power point (MPP) of the solar
cell, i.e. the point on the J-V characteristic of the solar cell, at which the solar cell has the
maximal power output. To optimize the operation of PV systems, it is very important, to
operate the solar cells (or PV modules) at the MPP. This is ensured with maximum power