Photovoltaic Cells for Very High Altitude Very Long Endurance Solar Aircraft

This proposed Phase II program will deliver a lightweight triple-junction solar cell that eliminates the current-matching bottleneck of current state-of-the-art InGaP/GaAs/Ge cells on Ge. This will be achieved by constructing a triple junction structure on the lattice constant of SiGe, allowing the integration of semiconductors with bandgaps that are optimized for the best possible triple-junction efficiency. The cell design proposed for Phase II has a practical achievable efficiency of 47% (AM1.5 spectrum without concentration), far exceeding the current record of 32% for the same illumination conditions. III-V cell development on the SiGe lattice constant is a natural direction for 4Power’s substrate platform which already utilizes SiGe graded buffers. This strategy for optimized solar cell efficiency is fully compatible with our Si-encapsulated cell technology demonstrated in Phase I. The multijunction cell that will be developed in Phase II will incorporate both Si encapsulation and uniquely accessible optimum bandgap profiles such that high volume/low cost production of ultra-high specific power cells in a Si-compatible manufacturing environment is enabled.