Material and device characteristics of InAs/GaAsSb sub-monolayer quantum dot solar cells

We have studied the material and photovoltaic characteristics of InAs/GaAsSb sub-monolayer quantum dot solar cells (QDSCs) with different Sb contents of 0%, 5%, 15%, and 20%. All QDSCs exhibit an extended external quantum efficiency (EQE) response in the wavelength range of 960–1000 nm that corresponds to sub-bandgap photon absorption. As Sb content increases from 5% to 20%, the cutoff wavelength in the EQE extends towards longer wavelength whilst the EQE in the wavelength region of 300–880 nm is lowered due to increased defect density. Compared to the QDSC (Sb 0%), an Sb incorporation of 5% enhances the short-circuit current density from 20.65 to 22.15 mA/cm2 induced by Sb surfactant effect. Since the open-circuit voltage and fill factor of the QDSC (Sb 5%) are comparable to those of the QDSC (Sb 0%), an enhancement in solar cell efficiency (10.5%) of the QDSC (Sb 5%) is observed. Further increasing Sb content to 15% and 20% results in the degradation of solar cell performance due to increased nonradiative recombination and large valence band offset in a type-II band line-up.