On the Need for Low Energy Proton Testing of Space Solar Cells

A quantitative analysis of low energy proton effects on space solar cell materials is presented. The results show that the space environment produces a uniform damage distribution, so any effects caused by the non-uniform damage profile induced by monoenergetic ground testing will not be seen on orbit. The solar cell space radiation response is shown to be best represented by ground testing with protons of high enough energy to fully penetrate the solar cell active region (on the order of 1 MeV or greater). Calculations are also performed for the case of an unshielded solar cell representative of a thin-film solar cell. A non-uniform damage profile is observed in an unshielded cell, but the profile is seen to decrease with depth with no Bragg peak forming. Therefore, ground testing at extremely low energies where the proton stops within the cell active region does not accurately model the space environment effects. Addition of a coating as thin as 10 mum is seen to render the damage profile essentially uniform