A critical review and discussion of different methods to determine the series resistance of solar cells: Rs,dark vs. Rs,light?

Luminescence imaging, both in electroluminescence and photoluminescence mode, is employed to test the widely accepted notion that the lumped series resistance, Rs, measured in the dark, Rs,dark, differs from its value measured under illumination, Rs,light. Using the illumination intensity variation method to determine the series resistance allows us to treat measurements in the dark and under illumination on equal footing. We find (i) the already-known variation of Rs along the current–voltage characteristic in dependence on the total dark current ID and (ii) that for standard operation conditions there is no difference between Rs,dark and Rs,light but only for external currents Iext exceeding the 1-sun photocurrent. Previously reported differences are traced back to systematic errors in the Rs evaluation schemes used in those works.