Ultra-lightweight and flexible inverted metamorphic four junction solar cells for space applications

In this work an inverted metamorphic four junction (IMM4J) solar cell with 30.9% conversion efficiency in beginning of life conditions under the AM0 (1367 W/m2) spectrum is presented. Additionally, our newest improved IMM3J cell, consisting of Ga0.51In0.49P/GaAs/Ga0.73In0.27As subcells, with 30.6% efficiency is also shown. The IMM4J solar cells consist of Al0.05Ga0.46In0.49P/Al0.14Ga0.86As/Ga0.89In0.11As/Ga0.73In0.27As subcells and are epitaxially grown by metal organic vapor phase epitaxy (MOVPE) on a GaAs substrate. These IMM solar cells achieve power-to-mass ratios of 3 W/g or more, which is more than three times higher than standard germanium based triple or four junction space solar cells. The losses in comparison to the simulated near-term potential efficiency of 33.8% for the IMM4J are analyzed in detail. Furthermore, the irradiation behavior for 1 MeV electron fluences of 1 × 1014 e-/cm2 and 2.5 × 1014 e-/cm2 for the IMM4J cells was investigated. A roadmap to further develop this concept towards an IMM5J with a realistic begin of life (BOL) efficiency potential of 35.9% under AM0 is presented.