GaInNAsSb Solar Cells Grown by Molecular Beam Epitaxy

The first GaInNAsSb solar cells are reported. The dilute nitride antimonide material, grown by molecular beam epitaxy, has a bandgap of 0.92 eV and maintains excellent carrier collection efficiency. Internal quantum efficiency of nearly 80% at maximum is obtained in the narrow bandgap GaInNAsSb cells. The short-circuit current density produced by the GaInNAsSb cells underneath a GaAs sub-cell in a multijunction stack, determined from the overlap of the quantum efficiency and the low-AOD spectrum, is 14.8 mA/cm². This is sufficient to current match the GaInNAsSb sub-cell to the other sub-cells in a GaInP/GaAs/GaInNAsSb solar cell. However, the open-circuit voltage and fill factor of the antimonide devices, 0.28 V and 0.61, are somewhat reduced when compared to GaInNAs devices with 1.03 eV bandgaps. The GaInNAsSb devices had wider depletion regions, which improves the collection efficiency but adversely affects the fill-factor and dark current by increasing depletion region recombination.