I INTRODUCTION
Monocrystalline epitaxial lift-off GaAs solar cells with high-quality mirrors have now been produced with efficiency of 28.8% under a simulated AMl.5G spectrum at 25°C [1]. This level of monocrystalline GaAs solar cell efficiency is not surprising in the context of the detailed balance limit of 33.2% and over 40 years [2] of research and development. Perhaps of greater interest is the large difference between the reported record polycrystalline GaAs solar cell at 18.4% [1] and the ∼ 57% increase up to 28.8% for the monocrystalline variant. Another direct bandgap solar cell material, CdTe, has reached 18.3% efficiency as a polycrystalline film [1] (and now 18.7% according to a recent press release from First Solar). If CdTe is developed into monocrystalline solar cells, will it be possible to achieve a similar improvement of about 50% in device efficiency as recently accomplished with GaAs? We attempt to answer this question here from a modeling perspective using material parameters such as carrier lifetime measured in newly designed double heterostructures.