Mechanism of anomalous degradation of silicon solar cells subjected to high-fluence irradiation

We have found anomalous degradation of electrical performance in silicon solar cells designed for space use due to high-fluence irradiation of charged particles, e.g., 1 MeV-electrons of ~10¹⁷ e/cm² and 10 MeV-protons of ~10¹⁴ p/cm². This anomalous degradation has two typical features, i.e., sudden-drop-down of electrical performances and slight recovery of the short circuit current I_SC just before the sudden-drop-down, which cannot be explained by a conventional model based on decrease of the minority-carrier life-time. In order to account for these features, we propose a new model, in which decreases of the majority-carrier concentration and the minority-carrier mobility are considered in addition to that of the minority-carrier life-time. The anomalous degradation observed is well represented by this model