Improved model for predicting space performance of solar cells

The radiation degradation produced in solar cells by the energetic charged particles of space is an important design constraint for many space missions. Since the original degradation estimates for Telstar¹ by Brown and Rosenweig, a series of reports sponsored by NASA^{2, 3, 4} have reflected the development of increased environment definition and solar cell degradation understanding. These reports have treated the degradation of the solar cell primarily by bulk displacement damage through the use of an experimentally determined damage coefficient. Inherent in the external damage coefficient approach is the assumption that 1) radiation damage in the solar cell structure is uniform, and 2) that the effect of the damage on cell response is uniform across the cell. It is these assumptions that lead to many of the functional dependencies of the damage coefficients on such variables as fluence, light spectra, and particle angle of incidence. These assumptions also render the method inadequate in dealing with low energy proton damage which is very nonuniform within the cell. Further, the assumptions of uniformity of damage and response put limitations on the accuracy that can be expected in evaluating cell response to space radiation spectra which produce nonuniform damage profiles across the cells. These problems have long been recognized and various models have been proposed to deal with the nonuniform damage production and response.