Direct observation of defects in triple-junction solar cell by optical deep-level transient spectroscopy

The optical deep-level transient spectroscopy (ODLTS) technique has been used to measure defects in GaInP/GaAs/Ge multi-junction solar cells for the first time. Three modes of ODLTS were used to detect defects in the top two sub-cells of this triple-junction cell separately. For one non-irradiated sample, only one level in the top sub-cell at low temperature was observed. Three samples were irradiated by 100 keV, 130 keV and 170 keV low-energy protons, respectively, and several levels were observed. By computational simulation, the distributions of radiation-induced defects in the samples were given. In the n⁺/p GaInP top sub-cells, the levels HT1 and ET1 appeared in both 130 keV and 170 keV proton-irradiated samples. In the n ⁺/p GaAs middle sub-cells, the level HM1 also appeared in both the samples.