Preliminary On-Orbit Performance Data from GaAs on Si Solar Cells Aboard MISSE5

GaAs on Si (GaAs/Si) solar cells grown on Si substrates coated with a step graded buffer of Si_xGe_1- alloys graded to 100% Ge have demonstrated AM0 efficiencies in excess of 17%. This technology offers the potential for significant increases in mass specific power (kW/kg) due to the low density and robust nature of the silicon substrate. Concerns exist that this III-V on Si technology may degrade when used in an application with significant thermal cycles due to the ~60% difference in thermal expansion coefficients. To examine this potential problem, devices were developed and launched to the International Space Station for on-orbit testing aboard Materials International Space Station Experiment number 5 (MISSES). In low Earth orbit, the devices are experiencing up to 100degC thermal cycles every 90 minutes. Data telemetered from MISSES indicates that the devices have successfully completed <6 months of on-orbit testing with no degradation observed