Radiation Degradation of Multijunction III-V Solar Cells and Prediction of their Lifetime

Degradation of multijunction GaInP/Ga(In)As/Ge solar cells under irradiation by 3 MeV electrons has been investigated. The dependencies of minority charge carrier life time on the 3 MeV electron fluence (up to 2·10 cm) have been calculated from the spectral characteristics of GaInP and Ga(In)As subcells experimentally obtained in their base layers, and the damage coefficients have been determined. Comparison of the obtained coefficients with literature data for 1 MeV electrons has been performed. It has been shown that the increase of the damage coefficients with the electron energy cannot be explained only by the increasing number of created defects. An approach to describe the dependence of the damage coefficient of a material on the acting particle energy based on the Kinchin-Pease model and on the hypothesis on formation of defects of multiple types in the solar cell structure, the ratio of concentrations of which is proportional to the particle energy. An analysis of the effect of deviation of the radiation action from the rated one on the SC resource limited by the preset decrease of its efficiency has been done.