Degradation behaviour of electrical properties of inverted metamorphic four-junction (IMM4J) solar cells under 1 MeV electron irradiation

In this study, the degradation effects of inverted metamorphic four-junction (IMM4J) solar cells were investigated after 1 MeV electron irradiation using spectral response and electrical property measurements. The results show that, similar to traditional tri-junction (TJ) GaInP/GaAs/Ge solar cells, the electrical properties (such as Isc, Voc, and Pmax) degrade as a function of logφ, where φ represents the electron fluence. In particular, the degradation of Voc is more serious than that of Isc because of the sum rule for Voc and the limit rule for Isc in IMM4J cells. Analysis of the spectral response curves indicates that, unlike traditional TJ cells, the In0.3Ga0.7As (1.0 eV) sub-cell exhibits the most severe damage in the irradiated IMM4J cells and the In0.58Ga0.42As sub-cell becomes a limits part for the electrical properties of the IMM4J solar cells.