Limiting Efficiency of Heterojunction Solar Cells

A heterojunction solar cell consists of a p-n junction between a high-bandgap and a low-bandgap semiconductor. As the cell is made up of two different semiconductors, the funda- mental question that arises is whether the limiting efficiency of the heterojunction solar cell is determined by the low-bandgap semiconductor, the high-bandgap semiconductor, some value in- between or, perhaps, even some other value exceeding the limiting efficiency of single gap solar cells. In this respect, in this paper, we demonstrate that the limiting efficiency lies in-between, without the absolute limiting efficiency of single gap solar cells being exceeded. However, in spite of this result, we find that the open-circuit voltage of heterojunction solar cells can exceed the bandgap (divided by the electron charge) of the low-bandgap semiconductor, something that is not possible in single gap solar cells.

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