  Perovskite/Si tandem solar cells have the potential to considerably
out-perform conventional solar cells. Under standard test conditions,
perovskite/Si tandem solar cells already outperform the Si single junction.
Under realistic conditions, however, as we show, those tandem solar cells are
hardly more efficient than the Si cell alone. We model the performance of
realistic perovskite/Si tandem solar cells under real-world climate conditions,
by incorporating parasitic cell resistances, non-radiative recombination, and
optical losses into the detailed-balance limit. We show quantitatively that
optimizing these parameters in the perovskite top cell, perovskite/Si tandem
solar cells reach an efficiency advantage of up to 14% absolute, even while
leaving the Si cell untouched. Despite the rapid efficiency increase of
perovskite solar cells, our results emphasize the need for further material
development, careful device design, and light management strategies, all
necessary for highly efficient perovskite/Si tandem solar cells.
