How to precisely measure OPV/DSSC/Perovskite solar cells?
With the leap-forward development of OPV, DSSC and Perovskite(PVK) solar cells, many research teams have developed the solar cells with the conversion efficiency more than 10%. However, the measurement method of these new type of solar cells is different from the crystalline silicon solar cells. These solar cells have a slower reaction time to light compared to silicon solar cells. Also, one of key factors is the correction of spectral mismatch. Because OPV/DSSC/PVK and Si solar cells have different spectral responses, which is called spectral mismatch, the correction of spectral mismatch has to be done before adjustment of light intensity. Use an appropriate solar reference cell can minimise the spectral mismatch which enables to avoid the measurement errors.
2. Spectral Mismatch correction
It provides a method to analyze the characterization of solar simulator according to the cited standard IEC 60904-9. Solar reference cell is commonly used to adjust the intensity of solar simulator. Nevertheless, there is always a spectral mismatch caused by the bias error of the simulator spectrum from the standard spectrum AM 1.5G, it still has±25% bias error even for a class A solar simulator. When the spectral response between solar reference cell and test sample is different, the spectral mismatch factor is calculated to correct the radiance according to the IEC 60904-7 international standard.
The spectral response data of solar simulator and OPV solar cells is given in Figure 1.
Fig. 1. SR data of solar simulator and OPV solar cells
Calculation of spectral mismatch according to IEC 60904-7 as formula (1)
is referred to as reference spectral irradiance AM 1.5G； is referred to as the measurement of the experimental spectrum of light source； is the spectral response of solar reference cell used for calibrating the intensity of solar simulator； is the SR of the test sample. The currents (I) is given by the spectral irradiance and spectral response of solar reference cell:
and is the coverage of the measurement wave-length range. The spectral mismatch factor (MM) is computed by the short-circuit current of reference spectrum AM1.5G with a test sample and the simulator spectrum with a test sample. As shown in equation (2):
Reference solar cell is used to adjust the intensity of a solar simulator, which ensures the short-circuit current produced by the reference cell through spectral mismatch correction is equivalent to its calibrated short-circuit current
Si reference cell is most commonly used to calibrate solar simulator and Si is the most popular material for solar cell, of which the spectral responses are very close and the mismatch factor can be ignored. Nevertheless, OPV/DSSC/PVK are new type of solar cells which have different spectral responses (as shown in the Fig. 2.), spectral mismatch correction is You can see the mismatch is huge if the Si solar reference cell is used to adjust the intensity of solar simulator. As for DSSC/OPV solar cells, you can choose KG5 window material. And since LBG-OPV has a wider spectrum response than OPV solar cell, KG3 is more recommended than KG5.
|Spectral Mismatch Factor MMF|
Fig. 2. Spectral response of different materials
3. Spectral response of reference solar cell with different window materials
Spectral mismatch correction is required in order to reduce the measurement bias error, as mentioned earlier, using a solar reference cell can ensure a minimal spectral mismatch. In theory, the solar reference cell should be made from the same material as the test sample because of the same spectral response. However, given that most of materials are less stable and has the tendency of degradation, selecting the combination of Si solar cell as substrate and different window material to achieve its spectral response and minimise the spectral mismatch, as shown in the figure 3.
Fig. 3. Spectral response of different Windows
Using OPV as an example, you can select KG5 as the window material of solar reference cell which it is spectrally matched to the OPV samples and ensures a minimal spectral mismatch. The calculation of spectral mismatch factor for DSSC, OPV, Low Band-Gap OPV and PVK solar cells is given in Table 1.
Under Standard Testing Conditions, the bias error caused by the mismatch can vary greatly by the used light source spectrum and the spectral responses of the solar reference cell and the test sample. Select the Si solar cell which has a better stability with appropriate window material to minimise the spectral mismatch. For DSSC/OPV solar cells, use KG5 solar reference cell to adjust the intensity of solar simulator, and KG3 solar reference cell for LBG-OPV type.
The recommended model for your device as shown in the following table 2:
|Your Device||Recommended Model|
|a-Si||Si + KG5 Filter|
|OPV||Si + KG5 Filter|
|Low Band Gap OPV||Si + KG3 Filter|
|DSSC||Si + KG5 Filter|
|Perovskite||Si + PVK Filter|