Intermediate band solar cells using in-plane ultrahigh-density InAs/GaAsSb quantum-dot sheets

In-plane ultrahigh-density InAs QDs with 5×10¹¹cm^-2 were successfully grown on the GaAsSb/GaAs(001). The QD sheets with type-1 and type-2 band structures were inserted into the pn-GaAs solar cells. In spite of only one QD sheet, the additional quantum efficiency was clearly observed at a long wavelength region of 900~1200 nm. The additional quantum efficiency for the type-2 QD cell was obtained at a wide wavelength region (1400 nm) and was higher than that for the type-1 QD cell. However, the open circuit voltage for the type-2 QD cell decreased as compared with that for type-1 QD cell. In addition, a separation distance from the p-layer to the type-1 QD sheet influenced on the cell performance.