III?V/SiGe on Si radiation hard space cells with Voc>2.6V

We have achieved the first monolithically integrated triple-junction InGaP/GaAsP/SiGe solar cell on Si substrate, achieving an adjusted efficiency of 20% AM0 1-sun. The practical achievable maximum AM0 efficiency for the optimal cell near this lattice constant is 39%. The combination of this high efficiency with the ability to process such cells on larger area lower-cost silicon substrates motivates our continued advancement of this technology. Radiation testing of 4Power cells, up to 2.7 × 10¹² p+/cm² (10MeV) show excellent radiation hardness; the novel SiGe bottom junction shows no measurable degradation after proton radiation testing, verifying such cells have application in air and space photovoltaics. Furthermore, because of the combination of high efficiency and low mass density, 4Power InGaP/GaAsP/SiGe solar cells can reach AM0 specific power approaching 1400 W/kg, greatly exceeding that of current state of the art InGaP/(In)GaAs/Ge space cells that are ~500 W/kg. The high efficiency afforded by the unique tailoring of the multijunction bandgap cell can provide a realistic maximum of ~500 W/m² at AM0 1-sun.