Thermal annealing effects of InGaAs (1.0 eV) and InGaAs (0.7 eV) sub-cells of inverted metamorphic four junction (IMM4J) solar cells under 1 MeV electron irradiation

In this work, thermal annealing effects of InGaAs (1.0 eV) and InGaAs (0.7 eV) sub-cells for inverted metamorphic four junction (IMM4J) solar cells after being irradiated by 1 MeV electrons are investigated by using light I - V characteristic, dark I - V characteristic and spectral response. Annealing temperature range is 60–180 ℃ and annealing time is 0-180 min. The results indicate that the open-circuit voltage V oc , short-circuit current I sc , and maximum power P max of two sub-cells are gradually recovered with annealing time increasing, and the rate of recovery increases with annealing temperature increasing. Besides, the recovery rate of InGaAs (1.0 eV) sub-cell is less than that of InGaAs (0.7 eV) sub-cell under the same annealing temperature and time. Double exponential model is used to fit the dark I - V curve for the key parameters (the serial resistant R s , the parallel resistant R sh , the diffusion current I s1 and the recombination current I s2 ). It is found that R s , I s1 and I s2 of two sub-cells decrease gradually and R sh increases during annealing and the rate of recovery increases with annealing temperature rising. However, the recovery of I s1 and I s2 of InGaAs(1.0 eV) are much greater than that of InGaAs(0.7 eV). The equivalent model between short-circuit current density ( J sc ) and defect concentration (N) induced by irradiation and annealing is established. N changes follow the first reaction kinetics, and the rate constant follows the Arrhenius equation with the annealing temperature. Therefore, the thermal annealing activation energy of InGaAs(1.0 eV) and InGaAs(0.7 eV) sub-cells are 0.38 eV and 0.26 eV, respectively. These efforts will contribute to the IMM4J solar cells, in particular, to space-based applications.