AlGaAs/InGaP MBE-grown heterostructures for 1.73eV Solar Cells With 18.7% Efficiency

Today's most efficient III-V solar cells rely on InGaP materials and are mostly grown by metal organic vapor phase epitaxy (MOVPE). Here, we report on an AlGaAs-based solar cell grown by solid source molecular beam epitaxy (MBE), with a certified conversion efficiency of 18.7%, and a 1.73eV bandgap designed for Si-based dual junction tandem devices. Material characterizations were carried out using Hall effect, secondary-ion mass spectrometry (SIMS) and X-Ray diffraction for the optimization of growth parameters of two conventional homojunction AlGaAs and InGaP solar cells. External quantum efficiencies (EQE) and I-V measurements demonstrate issues related to n-type AlGaAs and p-type InGaP layers. We show an important efficiency increase by merging the best of each structure: a thick p-AlGaAs base with tunable bandgap, and a thin 50 nm InGaP emitter.