Middle Cell Development for Wafer-Bonded III-V//Si Tandem Solar Cells

This article focuses on the material properties of two III-V semiconductors, AlGaAs and GaInAsP, and their usage as middle cell absorber materials in a wafer-bonded III-V//Si triple-junction solar cell. To this end single-junction solar cells were grown epitaxially lattice matched on GaAs wafers using metalorganic vapor phase epitaxy. By optimizing the growth temperature and the V/III ratio we could increase the open-circuit voltage at a target absorber band gap of 1.50 eV by up to 100 mV. In the future these results will be implemented into two-terminal III-V//Si triple-junction solar cells to increase the conversion efficiency beyond 35% under the AM1.5g solar spectrum.