Three-terminal tandem solar cells with a back-contact type bottom cell

In this paper, the authors analyze three-terminal tandem solar cells with a back-contact type bottom cell, in which III-V compound materials are stacked on a substrate of IV materials. This structure reduces loss resulting from current mismatch of the Ge bottom cell and resistance loss caused by tunnel junction at the GaAs/Ge interface. It is expected that the structure will achieve a high efficiency. They carried out calculations to find the relationship between carrier transportation characteristics and energy bands and to obtain I-V curves of the tandem solar cells. They found that the structure fulfills solar cell functions.