Radiation-Induced Changes in Silicon Photovoltaic Cells

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Abstract
The effect of both electron and proton irradiation of silicon photovoltaic cells is given in terms of the loss of photovoltaic response and the decrease in the lifetime. Analysis of the spectral response shows that a simple carrier diffusion model provides an adequate description of the behavior of the shallow-diffused junctions that were investigated, and yields values for the minority carrier diffusion length before and after irradiation. Most of the photovoltaic response is shown to occur in the base region of the cells, rather than in the surface layer, and virtually all of the loss of response is caused by defects introduced in the base. The reciprocal of the lifetime is linear with the cumulative irradiation flux, and is consistent with the loss of photovoltaic response. There are significant differences between p on n and n on p cells under electron bombardment; the former damaging roughly 100 times as rapidly as the latter. Under proton bombardment the difference is roughly a factor of three. A comparison of electron, proton, and neutron irradiation suggests that the individual lattice displacements produced in electron irradiation are no more effective in producing recombination than the displacements produced in high concentration in neutron and proton irradiation.