Experimental results from performance improvement and radiation hardening of inverted metamorphic multi-junction solar cells

This paper discusses results from continued development of inverted metamorphic multijunction (IMM) solar cells with air mass zero (AM0) conversion efficiencies greater than 34%. An experimental best four-junction IMM (IMM4J) design is presented. In an effort to improve IMM performance in space radiation environments, 1-MeV electron irradiation studies are conducted on the individual IMM4J subcells. These data are used to engineer an IMM4J structure with beginning of life AM0 conversion efficiency of approximately 34% and an end of life (EOL) remaining factor greater than 82%, where EOL is defined as performance after exposure to 1-MeV electron irradiation at 1E15 e/cm $^2$ fluence. Next-generation IMM designs are explored and an avenue toward AM0 conversion efficiencies of greater than 35% is presented.