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Ian Marius Peters1 H. S. Laine2 Liu Haohui3 Sarah Elizabeth Sofia1 Tonio Buonassisi1

1, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
2, Aalto University, Espoo, , Finland
3, National University of Singapore, Singapore, , Singapore

Two conflicting characteristics compete where the commercial viability of one-sun tandem solar cell is concerned: On the one hand, tandem solar cells have fundamentally higher efficiencies than single junction solar cells. On the other hand, tandem solar cells are intrinsically more complex than single junction solar cells and require more fabrication steps, which makes them more expensive. Only if the benefit from the additionally generated energy outweighs the higher fabrication cost can tandem solar cells be successful.
The question under which conditions the last sentence is true is a multilayered one. The value of efficiency is highest when considering the integrated PV system, which makes it necessary to explore system level aspects. These aspects include, among others, economic considerations as well as topics from material science; for example degradation.
In this work we attempt to provide a comprehensive overview about what is needed to make tandem solar cells economically successful. This overview includes a review of recent result in the field of tandem solar cell cost modelling, as well as some of our own result on this topic. Central to our findings is the concept of a “marriage of equals”, which states that the sub cells in a tandem should be similar, as well as enable high efficiencies. We will take a look at different material pairings, including perovskite on silicon, III-V on silicon and thin-film on thin-film tandems and investigate how these tandems compare to single junction solar cells in various types of systems and various locations.
We find that under the right circumstances one-sun tandem solar cells can outperform single junction solar cells economically. Yet more than techno-economic considerations are needed to make these types of solar cell a wide-spread reality. As an outlook we hope to offer a perspective of future opportunities for this technology.

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