Radiation degradation and damage coefficients of InGaP/GaAs/Ge triple-junction solar cell by low-energy electrons

Low-energy electrons were irradiated to InGaP single-junction and InGaP/GaAs/Ge triple-junction (3J) solar cells. The electron energy values were selected to approach the threshold energy of gallium and indium atoms recoiling in the InGaP lattice system (~300 keV). Simultaneous electron irradiation and current-voltage characteristics measurement of the cells revealed the fact that the short-circuit currents (Isc) of InGaP cells and consequently the 3J cells does not degrade when the cells are irradiated with electrons with energies of less than 300 keV, while the open-circuit voltage (Voc) considerably degrades for both types of cells, independent of electron energy. This result implies that the effects of radiation-induced defects originating from the recoil of phosphorus are insufficient to degrade the minority-carrier lifetime in InGaP. In addition, the degradation of the Voc is considered attributable not to an increase of reverse saturation current but to the increased surface recombination for irradiations with <; 300 keV electrons. The relative damage coefficients (RDCs) of the 3J cell were derived using the degradation trend obtained. The RDCs for Isc approximately followed the extrapolation line from high-energy electron irradiation results, but those for Voc were lower than the extrapolation.