Effect of irradiation damage on the dark electric properties of single junction GaAs/Ge solar cells

In this paper, the dark electrical properties are studied by measuring the dark current-voltage characteristics of a type of domestic single-junction (SJ) GaAs/Ge solar cell after proton irradiation. Using a double exponential mode for the dark electrical properties of p-n junction, the dark I-V curves of the proton-irradiated SJ cells are mathematically fitted, and there are four kinds of typical parameters, namely serious resistance (R-s), parallel resistance (R-sh), diffusion current (I-s1), and recombination current (I-s2), which are determined to characterize the irradiation effects. Hence, four parameters such as R-s, R-sh, I-s1 and I-s2 are significantly changed after proton irradiation, where R-s, R-sh, I-s1 increase while R-sh decreases with increasing the displacement damage dose. In addition, R-s increases with displacement damage dose, which is unrelated to proton energies. Theoretical analysis indicates that the above-mentioned changes of the parameters result from the damage distributions in different regions of the solar cells. Irradiation-induced damage in the base and emitter regions of the cells could induce R-s and I-s1 to augment, while junction-region damage causes the R-sh to decrease but the I-s2 to increase.