High Power Density III-V Cells for Ultralight Aircraft

Ultralight III-V solar cells are proposed to extend the mission duration of unmanned air vehicles (UAVs). Silicon panels used with an already flying UAV have panel power densities of 400 W/kg, using 15% AM0 thin (110 um) silicon cells. Here we propose using even thinner (8 um), higher efficiency (25% AM0), InGaP/GaAs tandem cells, bonded to thin coverglasses, to greatly increase the cell power density. Cells are first fabricated on thicker substrate wafers, and these wafers are later removed once the cells are bonded to thin (3 mil) CMG coverglasses. Panel power densities almost four times greater (1500 W/kg) than that offered by silicon should result from the higher efficiency and much lighter weight of the proposed cells. In Phase I, single-junction (10% AM0) GaAs cells would be made and bonded to 3 mil CMG coverglass with RTV adhesive. The substrates would then be removed with a selective etch. The wafer backs would then be metalized, and completed cells would be available at the end of Phase I for evaluation. In Phase I, a design study would also be performed to identify the best technology (e.g. adhesives vs. electrostatic bonding, epitaxial liftoff vs. selective etching) to pursue in Phase II. In Phase II, tandem cells would be made, and the technology identified as best in the Phase I study would be developed in a process suitable for large areas and high-volume manufacturing.