Electron Beam Dosimetry for Space Solar Cell Radiation Qualifications

The implications of common dosimetry methods used in electron beam irradiations for the space qualification of photovoltaics are described. The maximum power degradation of advanced solar cell technologies is compared as a function of electron fluence obtained from two electron irradiation facilities. The significant difference in the degradation rates between the two facilities suggests a systematic error in the electron fluence. The difference in dosimetry is examined using MCNP6.2 Monte Carlo simulations for ionizing and displacement damage dose (DDD) depositions along the electron beam path for each facility. It is shown that the 1-MeV electron beam flux, as determined from ionizing dosimetry methods, is overestimated by >24% compared to a nonionizing dosimetry counterpart. The error results from not properly accounting for the degradation of the electron beam energy and flux through the beam window and air gap.