On the detailed balance limit of ideal multiple bandgap solar cells

The detailed balance limit of the performance of multiple bandgap solar cells is revised. An approach is presented which uses, for each cell, back reflectors and front energy filters for restricting the energy range of the emitted electroluminescent photons to that of the incident radiation. This approach results in the highest calculated limiting efficiencies reported to data for a stack with a finite number of cells. It is emphasized that the same efficiency achieved at the highest light concentration can be obtained at any lower concentration, provided that the solid angle of the emitted photons can also be restricted to that of the incident light