Thin 5-Junction Solar Cells with Improved Radiation Hardness

Besides the efficiency, the radiation hardness of a solar cell is one of the key parameters for space applications. Today´s GaInP/GaInAs/Ge triple-junction solar cells achieve remaining factors for pmpp of 88 % after 1 MeV electron irradiation at a fluence of 10¹⁵ cm^-2. The degradation is dominated by the GaInAs middle cell. New solar cell structures with 5 pn-junctions have been developed to further improve the radiation resistance and excellent remaining factors of 95 % for V_oc and 93 % for pmpp are reported in this paper. The structure consists of AlGaInP, GaInP, AlGaInAs, GaInAs and Ge active pn-junctions. A 1.1 mum thin Ga_0.99In_0.01As 4^th subcell with a radiation hard layer structure was developed. This subcell has now a remaining factor for J_sc of 95 %. This proves the high radiation hardness of the 5-junction space solar cell concept