Governing factors and structural optimization of i-layer effects on irradiation degradation in AlGaInP solar cells under high-fluence 1 MeV electron irradiation

For III–V solar cells intended for space missions with high cumulative charged-particle irradiation, the incorporation of an intrinsic (i) layer has been widely regarded as an effective strategy for improving radiation tolerance. However, the dominant factors governing this improvement and the associated structural optimization strategy remain unclear. In this work, AlGaInP solar cells, typically used as the top subcell in upright metamorphic four-junction (UMM4J) solar cells, are investigated. Two structures with i-layer thicknesses of 60 and 120 nm are experimentally examined under 1 MeV electron irradiation. The results show that increasing the i-layer thickness from 60 to 120 nm causes no significant difference in maximum power ( P max ) degradation. To explain this result, a simulation model for 1 MeV electron-induced electrical degradation is established. Based on this model, the influence of base thickness, the material-dependent minority-carrier lifetime damage coefficient, and absorber-thickness variation on the radiation-hardening effect of the i layer is analyzed. The results indicate that the improvement is most pronounced when the combined thickness of the i layer and the base layer is 660 nm, with an i-layer thickness of 440 nm. At a fluence of 1 × 10 16 cm −2 , the corresponding P max remaining factor reaches 87.1%, nearly identical to that of the 60 nm i-layer structure investigated experimentally, while the initial P max is increased by 11.8%. This study provides guidance for radiation-tolerant structural optimization of AlGaInP top cells and other III–V solar cells.