Solar cell short circuit current errors and uncertainties during high altitude calibrations

High altitude balloon based facilities can make solar cell calibration measurements above 99.5% of the atmosphere to use for adjusting laboratory solar simulators. While close to on-orbit illumination, the small attenuation to the spectra may result in under measurements of solar cell parameters. Variations of stratospheric weather, may produce flight-to-flight measurement variations. To support the NSCAP effort, this work quantifies some of the effects on solar cell short circuit current (Isc) measurements on triple junction sub-cells. This work looks at several types of high altitude methods, direct high altitude measurements near 120 kft, and lower stratospheric Langley plots from aircraft. It also looks at Langley extrapolation from altitudes above most of the ozone, for potential small balloon payloads. A convolution of the sub-cell spectral response with the standard solar spectrum modified by several absorption processes is used to determine the relative change from AM0, Isc/Isc(AM0). Rayleigh scattering, molecular scattering from uniformly mixed gases, Ozone, and water vapor, are included in this analysis. A range of atmospheric pressures are examined, from 0.05 to 0.25 Atm to cover the range of atmospheric altitudes where solar cell calibrations are performed. Generally these errors and uncertainties are less than 0.2%.