Toward >25% Efficient Monolithic Epitaxial GaAsP/Si Tandem Solar Cells

We report here on progress made in the development of >20% efficient monolithic epitaxial III-V/Si tandem solar cells. Following our prior demonstration of a GaAs0.75P0.25/Si tandem cell with verified AM1.5G efficiency of 20.1%, we have undertaken intensive efforts aimed at optimization of the top and bottom subcells, involving both materials quality improvement and detailed device structure refinement. To date we have thus demonstrated 21.8% AM1.5G GaAs0.75P0.25/Si tandem cells making use of an optimized, but still defect-limited GaAsP top cell combined with a simple diffusion-processed (emitter and back-surface field) Si bottom cell. With recent development of a low dislocation density III-V-on-Si epitaxial materials platform, as well as bottom cell enhancements for photon management, analytical performance loss analysis and efficiency projections indicate that >25% is achievable in the near-term, and 30% within reach with additional holistic optimization.