Potential Optical Degradation of Spacecraft Solar Cells Under Low-Energy Proton Irradiation

A physical mechanism is considered that can explain the anomalous optical degradation of solar cells on spacecraft operating in medium-altitude circular orbits. This mechanism is based on the selective removal of oxygen atoms from oxides under proton irradiation. As a result of this exposure, a thin, modified SiOx layer with high absorbance within the spectral sensitivity range of the solar cells forms on the surface of the protective glass. Estimates showed that, under complete oxygen release, optical losses reach 7% for silicon solar cells and 17% for triple-junction GaAs-based solar cells, and the minimal proton fluence required is 2.2 × 1016 1/cm2. This fluence can be produced by plasmaspheric protons bombarding the charged surface of spacecraft.