Delta doping and positioning effects of type II GaSb quantum dots in GaAs solar cell

摘要

GaSb quantum dot (QD) solar cell structures were grown by molecular beam epitaxy (MBE) on GaAs substrates. We investigate the reduction in open circuit voltage and study the influence of the location of QD layers and their delta doping within the solar cell. Devices with 5 layers of delta doped QDs placed in the intrinsic, n and p regions of a GaAs solar cell are experimentally investigated and the deduced values of Jsc, Voc, Fill factor (FF), efficiency (η) are compared. A trade-off is needed to minimize the V_(oc) degradation while maximizing the short circuit current density (J_(sc)) enhancement due to sub-bandgap absorption. The voltage recovery is attributed to the removal of the QDs from the high field region which reduces SRH recombination. The devices with p or n doped QDs placed in the flat band potential (p or n region) show a recovery in J_(sc) and V_(oc) compared to devices with delta doped QDs placed in the depletion region. However there is less photocurrent arising from the absorption of sub-band gap photons. Furthermore, the long wavelength photoresponse of the n doped QDs placed in the n region shows a slight improvement compared to the control cell. The approach of placing QDs in the n region of the solar cell instead of the depletion region is a possible route towards increasing the conversion efficiency of QD solar cells.