Deep space degradation of Si and GaAs solar cells

Si and GaAs solar cells have been irradiated with 1 MeV electrons at low temperatures, i.e. in conditions of deep space missions. The current-voltage characteristics have been recorded under 0.11 AM0 illumination produced by a filtered Xe lamp at the temperature of the irradiation. The variations of the open-circuit voltage and short-circuit current have been monitored versus fluence up to 10¹⁶ electrons cm^-2, at temperatures ranging from 80 to 300 K. The maximum power degradation is found to be practically temperature independent in GaAs cells while it apparently reproduces the annealing stages of the introduced defects in Si cells. The variations of the short-circuit current with fluence and temperature can be understood in terms of the defect introduction rates in both Si and GaAs cases. These results indicate that, although the defect introduction rate can be larger in GaAs than in Si, the created defects appear more efficient to recombine minority carriers in Si than in GaAs