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

Optical absorption spectra of GaSb/GaAs quantum-ring-with-dot structures (QRDSs) are calculated using Fermi's golden rule by which the electronic states involved in the optical transitions are obtained from the eight-band k ⋅ p method. The absorption spectra of multi-stacked QRDS layers show that the interband and intraband transitions 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 based on 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 IB. The more efficient two-step photon absorption indicated by the enhancement of the EQE also suggests the potential of QRDSs for the IBSCs.