Infrared Reflective and Transparent Inverted Metamorphic Triple Junction Solar Cells

The infrared (IR) portion of the solar spectrum with photon energies below the lowest bandgap in III-V multijunction photovoltaic devices does not contribute to electrical power and is typically ignored during solar cell design. In a three junction inverted metamorphic multijunction (IMM) solar cell with a 1.0 eV bottom junction, this infrared light makes up 16% of the total power and can be extracted from the cell by reflective or transparent designs. We demonstrate several IMM designs that are about 39% efficient under concentration, allow this IR power to be used elsewhere, and reduce the heat load by about 20% relative to Ge-based solar cells that are also 40% efficient.