Internal voltages in GaInP∕GaInAs∕Ge multijunction solar cells determined by electroluminescence measurements

We analyze electroluminescence spectra of a $\mathrm{Ga}\mathrm{In}\mathrm{P}∕\mathrm{Ga}\mathrm{In}\mathrm{As}∕\mathrm{Ge}$ triple-junction solar cell at different injection currents. Using the reciprocity theorem between electroluminescent emission and external quantum efficiency of solar cells allows us to derive the current/voltage curves and the diode quality factors of all individual subcells.