GaAs single junction cells, representative of the middle cell in triple junction Ga 0.5 In 0.5 P/GaAs/Ge cells, were irradiated with various fluences of 1-and 3-MeV electrons as well as 1-MeV protons.The light I-V curves measured at room temperature exhibit a voltage-dependent photocurrent.The photocurrent is modeled taking into account the voltage-dependent width of the space charge region in combination with a strongly decreased minority carrier diffusion length. By extracting the width of the space charge region from capacitance measurements and the base layer diffusion length from the external quantum efficiency of the cell, the experimental behavior is reproduced accurately.
A method for measuring subcell capacitance voltage (C–V) in a multijunction solar cell is introduced. The subcell of interest is illuminated by a monochromatic light pulse with a ns rise time. The subcell capacitance is calculated from the measured rise time of the solar cell voltage. The effect of optical coupling is eliminated by introducing a high intensity bias illumination to all subcells below the one measured. The method is verified by comparing the subcell capacitance obtained from four junction solar cells with the results from corresponding component cells, which can be measured using well-established methods. From the C–V curves, the built-in voltage and the base layer doping density for each subcell are calculated.
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