Impedance spectroscopy characterization of proton-irradiated GaInP/GaAs/Ge triple-junction solar cells

Impedance spectroscopy (IS) measurements have been carried out to study the degradation of proton-irradiated GaInP/GaAs/Ge triple-junction (3J) solar cells. Four samples were irradiated with proton energies 40 keV, 100 keV, 130 keV and 4 MeV, respectively; the distribution of irradiation-induced defects was simulated by SRIM software. IS measurement and analysis show that parallel resistance and capacitance of each p-n junction for all the three sub-cells of the triple-junction solar cell could be deduced with a simple ac RC equivalent circuit. The optical method was used to distinguish the three measured RC units from each other. For the non-irradiated sample, the measured capacitance of each p-n junction agrees well with the calculated result, while for the irradiated samples, the variation of R and C of each sub-cell related with proton energy agrees well with the results of SRIM simulation.