A three-terminal double junction GaAs/GaAlAs cascade solar cell

This paper describes fabrication process and performances of a new type of monolithic solar cell with two junctions and bandgaps of 1.4 eV (GaAs) and 1.69 eV (GaAlAs) respectively, with the novel feature of only four epitaxial layers. The structure is a three-terminal device similar to a p-n-p transistor with a thick base. For the first prototypes, an overall conversion efficiency of 20.5 percent has been measured at 80 suns. It is expected that further optimization steps can lead to a conversion efficiency of 25 percent AM 1.5 for this structure.