Solar Cell Degradation under 1-Mev Electron Bombardment

The high-energy electron and proton radiation in the Van Allen Belt produces defects in semiconductors which cause a reduction in solar cell power output. This raises immediately the problem of assessing the expected useful life of the power plant of a satellite that passes through this radiation belt. The life is the time for which the power plant is capable of delivering the electrical power necessary for successful operation of the satellite. For an evaluation one has to determine the maximum power point under outer space solar illumination after various amounts of bombardment by protons of differing energies and by electrons of differing energies, with various thicknesses of shielding over the cells. Such 399 400 T H E B E L L SYSTEM TECHNICAL J O U R N A L , MARCH 1963 information may then be synthesized to yield the expected performance for a given Van Allen Belt spectrum under given shielding conditions. An attempt at a direct experimental investigation of these relations has the disadvantage of being exceedingly complex and involved. However, the complexity of this problem can be significantly reduced by recognizing that the solar cell performance is strongly dependent on the minority-carrier lifetime in the bulk of the material. This minoritycarrier lifetime is ordinarily the most radiation-sensitive parameter in a semiconductor, and a solar cell will, practically speaking, be useless due to minority-carrier lifetime degradation before any of the other determining parameters are significantly affected by radiation.