Measurement of PERC & other high efficiency modules on QuickSun solar simulators
Silicon solar cells have an internal capacitance which limits how fast they can be measured. This capacitance increases with voltage.
Duration of a IV curve measurement on a solar simulator is typically 6 – 40 ms. Here, also voltage sweep length is used to characterize the measurement duration.
Because internal capacitance of c-Si cells increase with voltage, voltage can be ramped up more quickly during the sweep near ISC. This makes it beneficial to use a double slope sweep, where the voltage is changed more slowly around the measurement of PMP.
Effective sweep time corresponds to the time a linear sweep would take when using the voltage ramp used during the measurement of PMP.
Using double slope voltage sweep, effective sweep time is 2.5 times longer than the measurement duration.
When voltage sweep is performed from ISC to VOC, voltage is increased. Part of the generated current is used to charge the internal capacitance. The result is that measured PMP is underestimated. When voltage sweep is performed from VOC to ISC, the internal capacitance discharges and the measured PMP is overestimated.
The graph above shows how PMP of a PERC module is affected by the effective sweep length.
The data is shown as a function of voltage ramp rate.
The center of graph corresponds to a zero ramp, which means a steady state measurement.
When IV curves of a forward (ISC→VOC) and backward (VOC→ISC) sweeps are combined, an estimate for a steady state result is obtained.
QuickSun can perform a 2-flash measurement, where 1st flash has forward sweep and 2nd flash backward sweep.
The two datasets are automatically combined to produce a near steady state result.
On the left, the blue curve represents a forward sweep, and the red curve the backward sweep. The combined IV curve is black.
QuickSun 550CE can measure reliably all technologies with high efficiency, such as PERC, HIT, and IBC modules.