Anomalous degradation in silicon solar cells subjected to high-fluence proton and electron irradiations

Distinct from the well-known logarithmic degradation in electrical performances of a crystalline silicon solar cell, an anomalous degradation of short-circuit current density ${\mathrm{(I}}_{\mathrm{sc}})$ was observed in a cell irradiated by energetic protons and electrons at high fluence. From results of proton irradiations with various energies (0.4–10 MeV) and high frequency (1 MHz) capacitance measurements, the anomalous drop of $I_{\mathrm{sc}}$ is found to be caused by (1) the $p$ -type substrate changes into the intrinsiclike layer (Fermi level shift) by the irradiations, followed by an extension of the depletion layer, and (2) the drift length of the minority carrier becomes shorter than the depletion layer.