Increased radiation resistance of thin 4J-IMM solar cells by recycling transparency photon losses

In this work we have evaluated thickness dependent efficiency of 4J-IMM solar cells as a function of radiation doses and dislocations. It's been shown that bottom 0.7ev InGaAs sub-cell's radiation resistance and/or dislocation tolerance can be improved by use of back gold reflection. Photon confinement results in fabrication of thinner sub-cells thus increasing the radiation hardness of the sub-cells. It's been shown that for moderate to high doses of radiation, very high EOL efficiencies can be afforded with substantially higher dislocation densities than those commonly perceived as acceptable for IMM devices i.e. even in the presence of dislocation densities in both sub-cells as large as 10⁷ cm^-2, for typical 10¹⁵ cm^-2 1MeV electron fluence, a remaining power factor >85% (ηEOL~32%). These finding could in turn be used to simplify manufacturing (thinner graded buffers) or/and increase yield for IMM space cells and also explain the irregular radiation behavior seen in 4J-IMMs.