Detailed balance limit of the efficiency of tandem solar cells

The fundamental (detailed balance) limit of the performance of a tandem structure is presented. The model takes into account the fact that a particular cell is not only illuminated by part of the solar irradiance but also by the electroluminescence of other cells of the set. Whereas, under 1 sun irradiance, a single solar cell only converts 30% of the solar energy, a tandem structure of two cells can convert 42%, a tandem structure of three cells can convert 49%, etc. Under the highest possible light concentration, these efficiencies are 40% (one cell), 55% (two cells), 63% (three cells), etc. The model also allows us to predict the ideal efficiency of a stack with an infinite number of solar cells. Such a tandem system can convert 68% of the unconcentrated sunlight, and 86% of the concentrated sunlight.