Suitability of GaAsBi as a Candidate Junction in a III-V Multi-Junction Solar Cell

The introduction of bismuth into GaAs results in a large band-gap bowing and a dramatic reduction in band-gap energy. This enables GaAs alloys containing dilute fractions of Bi to offer technologically useful absorption thresholds in multi-junction solar cells. Here we investigate the opportunity that GaAsBi holds as a component in an upright metamorphic solar cell architecture which, in principle, could offer a better match to the AM0 spectrum over the conventional InGaAs based UMM cell. We show that the strong and inherent alloy disorder associated with the dilute Bi fraction results in a degradation in the GaAsBi sub-cell by as much as 202 mV with 5.5% Bi incorporation. Despite this degradation in voltage we find that a potential GaAsBi based design that accounts for finite diffusion length and alloy disorder outperforms the conventional InGaAs UMM architecture at AM0, requiring only 2.8% Bi incorporation and 0.25% compressive strain.