Growth and characterization of a two-junction, stacked solar cell

Results are reported on an experimental two-junction cascade solar cell structure. The cell has been fabricated on a GaAs substrate using six or seven layers of GaAs and AlGaAs materials to form a monolithic, internally connected, two-junction structure. The lower cell has been fabricated in GaAs with a bandgap of 1.44 eV while the connecting junction and upper cell has been fabricated in AlGaAs with a bandgap in the range of 1.6 - 1.7 eV. The resulting cascade solar cell has a terminal I-V characteristic similar to that of a single p-n junction and under illumination exhibits an open circuit voltage of about 2.0 volts. This work demonstrates for the first time the cascade solar cell concept.