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 I
_sc
, V
_oc
, and P
_max
) degrade as a function of logφ, where φ represents the electron fluence. In particular, the degradation of V
_oc
is more serious than that of I
_sc
because of the sum rule for V
_oc
and the limit rule for I
_sc
in IMM4J cells. Analysis of the spectral response curves indicates that, unlike traditional TJ cells, the In
_0.3
Ga
_0.7
As (1.0 eV) sub-cell exhibits the most severe damage in the irradiated IMM4J cells and the In
_0.58
Ga
_0.42
As sub-cell becomes a limits part for the electrical properties of the IMM4J solar cells.