Abstract
We report on AlGaAs-based heterojunction solar cells grown by solid source molecu- lar beam epitaxy (MBE). We investigate InGaP and AlGaAs material quality and we demonstrate significant efficiency improvements by combining the best of each alloy: a thick p-AlGaAs base with tunable bandgap, and a thin 50 nm n-InGaP emitter separated by a thin intrinsic AlGaAs layer. We report a certified solar cell conversion efficiency of 18.7% with a 2-μm-thick AlGaAs layer and a bandgap of 1.73 eV, suit- able for high efficiency Si-based tandem devices.