intermediate band, quantum dot, solar cell, GaAs/GaSb
Experiments have shown that extrinsic intermediate band (IB) states, for instance, formed by artificial quantum dots (QDs), located in the depletion region participate in electron-hole recombination. This facilitates dramatically the dark current and reduces the open circuit voltage of IB solar cells. On the other hand, spatial separation of IB-states from the depletion region adds more flexibility for the cell design, eliminates dark current leakage through IB-states, and limits recombination through IB-states. The later enables generation of additional photocurrent by two-photon resonant absorption of concentrated sunlight in such QDs. In this report we present a model of a new GaAs IB solar cell with strained GaSb type-II QDs spatially separated from the depletion region into the p-doped part of the cell. We use continuity equations enforced by the detailed balance principle and non-radiative recombination through IB-states to calculate both photocurrents and efficiency of the cell. Our calculation shows that the newly proposed design may increase efficiency of GaAs solar cells from 30% to 50% in response to concentration of sunlight from 1-sun to 500-sun. Noteworthy, though non-radiative recombination in QDs degrades the efficiency, it is still above the Shockley-Queisser limit by 5% to 10%.