Multiple levels in intermediate band solar cells

The presence of multiple energy levels in the intermediate band solar cell (IBSC) is studied by detailed balance calculations under ideal conditions. Multiple levels are found experimentally in IBSCs made with quantum dots (QDs) which act to reduce the limiting efficiency determined from detailed balance calculations. $J_{\text{L}}\text{-}{V}_{\text{OC}}$ measurements up to 1000 suns on IBSCs are presented together with their fitting to modified detailed balance calculations. It is found that the introduction of the QDs degrades the performance of the host cell but the sub-bandgap cell operates close to ideality.