External quantum efficiency artifacts in partial-irradiated GaInP/GaAs/Ge solar cells by protons and electrons

Artifact is a special kind of phenomenon related to fluorescence coupling and shunt resistance in external quantum efficiency (EQE) measurements in multijunction (MJ) solar cells, and it is sensitive to the defects and damages. In this paper, the changes of artifacts were studied in partial irradiated MJ solar cells by common or two-dimension mapping Quantum Efficiency (QE) measurements. Simplified mathematical models and graphic analysis were applied to explain the mechanisms of changes of artifacts. Irradiation weakens the artifacts effects due to the decrease in relative fluorescence yield. Artifacts analysis results indicate that after 1 MeV electron irradiation, the open circuit voltage V_oc of GaInP subcell decays from 1.40 V to 1.35 V, and the reverse saturation non-radiative recombination current I₀₂ increases 3.7 times. Correspondingly, after 70 keV protons irradiation, the open circuit voltage V_oc decays to 0.90 V and I₀₂ increases 7550 times by EQE artifacts analysis. Lateral scanning of the partial damaged samples shows a smooth artifacts transition region that appears near the boundary of damaged region in MJ solar cells. This is found correlated with the difference in the lighted areas of bias light and EQE pulse spot. 2D artifacts analysis could properly explain the smoothness and shift of damage interface.