Spectral mismatch effect to the open-circuit voltage in the indoor characterization of multi-junction thin-film photovoltaic modules

The spectral mismatch between the standard AM1.5g spectral irradiance and the spectrum of a solar simulator is well-known to affect the measurement of the short-circuit current in the current-voltage (IV) characterization of both single and multi-junction photovoltaic (PV) devices, where it may result in deviations larger than 10% even on Class A simulators. Multi-junction devices may also give spectral mismatch effects on the open-circuit voltage, as discussed in this work. The effect is larger when the measurement is performed using isotype reference cells, that are conventionally preferred to broadband ones, giving a better estimation of the short-circuit current. Experimental evidence of systematic differences in the open-circuit voltage of 2-junction PV module measurement campaign are given, that may arise from such effect. The results stress the importance of using both isotype and broadband cells as reference in IV measurements of multi-junction PV modules, as well as a spectral mismatch correction procedure for the open-circuit voltage in a future standard procedure.