Electron Irradiation Effects and Defects Analysis of the Upright Metamorphic Four‐Junction (UMM4J) Solar Cells

Herein, 1‐MeV electron irradiation is conducted to the AlGaInP (1.89 eV)/AlInGaAs (1.45 eV)/InGaAs (1.14 eV)/Ge (0.67 eV) upright metamorphic four‐junction (UMM4J) solar cell and its upper three key subcells. Light IV (LIV), external quantum efficiency (EQE), and deep level transient spectroscopy (DLTS) measurements are implemented to analyze the degradation of electric properties and evolution of defects of the UMM4J solar cell. The LIV results illustrate that the short circuit current ( I sc ), open circuit voltage ( V oc ), and maximum power ( P max ) degrade as a function of the logarithmic change of the electron fluence. EQE curves confirm the excellent anti‐irradiation characteristic of the AlGaInP (1.89 eV) subcell. Three types of electron traps E 1 ( E c –0.16 eV), E 2 ( E c –0.47 eV), and E 3 ( E c –0.55 eV) are detected in the AlGaInP subcell. Two types of hole traps H 1 ( E v + 0.35 eV) and H 2 ( E v + 0.70 eV) are discovered in the AlInGaAs subcell and two types of hole traps H 3 ( E v + 0.05 eV) and H 4 ( E v + 0.36 eV) are observed in the InGaAs subcell. Nonionizing energy loss ( NIEL ) of 1‐MeV electrons in are calculated via Screened Relativist method. The defect concentrations show an approximately linear relationship with the displacement dose.