IEC 60904-7:2019 pdf download – Photovoltaic devices – Part 7: Computation of the spectral mismatch correction for measurements of photovoltaic devices.
All integrals shall be performed in the entire spectral range where the respective quantities are not zero. The irradiance distribution shall be known over the entire combined spectral range of sensitivity of the device under test and the reference PV device.
The spectral irradiance distributions and the spectral responsivities can be given on an absolute or relative scale.
If the relative test spectrum would be identical to relative reference spectrum, then the SMAI is 1 and spectral mismatch corrections can be neglected, even if the spectral responsivities of the devices differ. However, considering that the test spectrum as a physical quantity has a measurement uncertainty assigned to it that is not zero, the SiMi will still have a measurement uncertainty contribution different to zero. Thus, the SMM factor cannot be neglected when considering its measurement uncertainty contribution, though the value of the factor is 1.
If the relative spectral responsivity of the device under test would be identical to the relative spectral responsivity of the reference device, then the SMM is 1, even if the relative spectral irradiance distributions differ (perfectly matched reference device). Considering that both spectral responsivities have a measurement uncertainty that is not zero, the SMM will still have a measurement uncertainty contribution different to zero. Thus, the SM/V.! factor cannot be neglected when considering its measurement uncertainty contribution, though the value of the factor is 1.
Due to the irregular shape of the reference and measured spectra, spectral responsivities should be interpolated to the wavelength points of the spectral irradiance measurements, not vice versa.
Formula (3) is valid for single-junction devices, but may be used for multi-junction devices. For multi-junction devices, the calculation shall be performed for each junction in the device, using its spectral responsivity including the spectral filtering caused by the junctions above the junction under consideration. The test report should specify the spectral mismatch factors and the relative current generation of the individual junctions. For multi-junction devices, refer to IEC 60904-1-1 (l-V) and IEC 60904-8-1 (SR).
The spectral responsivities used shall be valid at the level of target irradiance for which the SMM factor applies because for non-linear devices they may vary with the level of irradiance.
Derivation of SMM
If the reference device and the device under test are of different dimensions (active area), the dimensions should be specified in the test report. b) If a perfectly matched reference device is used and no mismatch correction is applied, the identification of the device under test and the reference device, as well as the spectral responsivities of reference and device under tests according to their test report (IEC 60904-8 or IEC 60904-8-1) should be included in the test report. If the reference device and the device under test are of different dimensions (active area), the dimensions should be specified in the test report. If the spectral responsivity of the device under test cannot be measured, the test report should include the criteria used to define the equivalency of the spectral responsivities. c) Note that the spectral mismatch factor determined by applying this procedure is only valid for correcting a measurement of the specific device under test considered with the particular reference device and test spectrum used to calculate the SMM. When measuring this device under test under different spectral irradiance (being it simulated or natural sunlight) and/or with a different reference device, the spectral mismatch factor shall be recalculated.