Optical absorption spectra of GaSb/GaAs quantum-ring-with-dot structures and their potential for intermediate band solar cells

Abstract

Optical absorption spectra of GaSb/GaAs quantum ring-with-dot structures (QRDSs) are calculated by the Fermi’s golden rule which the electronic states involved the optical transitions are obtained from the eight-band k · p method. The absorption spectra of multi-stacked QRDS layers show the interband and intraband transitions that are favorable to intermediate band solar cells (IBSCs). A drift-diffusion model with rate equations for a solar cell containing multi-stacked QRDS layers is formulated according to the absorption spectra. The external quantum efficiency (EQE) determined by the model with the AM1.5 solar spectrum and additional infrared light demonstrates that the confined hole states in the quantum ring (QR) parts of the QRDSs effectively function as an intermediate band. More efficient two-step photon absorption indicated by the enhancement of EQE also suggests the potential of QRDSs for the IBSCs.

Theoretical Investigation and Improvement of Characteristics of InAs/GaAs Quantum Dot Intermediate Band Solar Cells by Optimizing Quantum Dot Dimensions

“…These cells exploit the ability to absorb sub-bandgap photons, transitioning electrons from the valence band (VB) to the intermediate band (IB) before ultimately transitioning them from the IB to the conduction band (CB). Consequently, photons with higher and lower energies than the bandgap can be absorbed, significantly enhancing cell efficiency [25,26]. Structures employing QDs as the intermediate band include InAs/GaAs, GaAs/AlGaAs, and InAs/AlGaAs [27][28][29][30].…”