Production ready 30% efficient triple junction space solar cells

Spectrolab presents its next production GaInP/GaAs/Ge space triple junction solar cell, the XTJ space solar cell, averaging 29.8% efficiency at maximum power (AM0, 28°C, 135.3 mW/cm²) at beginning-of-life (BOL) testing of large populations (845 cells) of large-area solar cells without coverglass. Bare cells from this population with area of 26.62 cm² have been tested to a maximum efficiency of 31.1% under the same AM0 testing. Additional optical and electrical performance characterization will be presented. XTJ is more than a BOL power improvement over heritage products. Bare cell radiation testing shows power retention at max power (NPmp) of 0.89 and 0.84 after irradiation with 1-MeV energy electrons to a fluence of 5e14 cm⁻² and 1e15 cm⁻², respectively. Environmental degradation testing of XTJ parts shows only 1.7% degradation for more than 4000 hours at 250°C and no degradation after 90 days at 95% r.h. and 45°C. Together these characteristics enable XTJ to be a 7% improvement in end-of-life cost of power on space flight panel over Spectrolab's 28% BOL efficient UTJ. Finally, XTJ engineering confidence thermal cycle testing and qualification status to the AIAA S-111-2005 standard will be elaborated.