The influence of Bi and Al content on the deep levels in InGaP and AlInGaP solar cell structures

InGaP/InGaAs/Ge 3-juction solar cells have proved to the most effective solar cells for space applications. Recently, AlInGaP was proposed as a top layer, which has the future prospects of super high efficient solar cells. However, the efficiency of the AlInGaP based multi-junction solar cells that are under investigation is not up to the expected levels. In order to understand the reason behind this low efficiency, we have explored role of Al content on native defects in the performance of AlGaInP solar cells. In addition, we have also explored the interaction of Bi on p-type InGaP and p-type AlInGaP solar cell structure. The Deep level transient spectroscopy (DLTS) was used to investigate the different characteristics of these observed defects and their possible role in low lifetime/efficiency of the solar cells. The four types of solar cell structures under investigation showed four electron traps and two hole traps. Detailed depth profile analysis showed that the hole traps generated in the Bi doped InGaP and Bi doped AlInGaP act as strong recombination centers. In view of this study, it has been concluded that the deep levels induced by Al Impurity and Bi impurity plays an important role in the low efficiency of InGaP/AlInGaP solar cells.