Towards High-Efficiency Ultra-Thin GaAs Solar Cells for Space Applications: A Comparative Study of Back Reflector Designs

The electrical performance of ultra-thin (300 nm absorber layer) thin-film epitaxial lift-off (ELO) GaAs solar cells, with five different back reflector designs (planar Ag, patterned Ag, patterned ZnS/Ag, textured Ag and textured ZnS/Ag) were compared to identify the most promising reflector design for this type of cell. It was found that cells with patterned ZnS/Ag, textured Ag and textured ZnS/Ag all show an increased short circuit current density (J
sc
) and thereby light conversion efficiency compared to cells with a planar Ag reflector, with the best results (15.4% J
sc
increase for cells with antireflection coating) obtained for cells with a textured ZnS/Ag reflector. Further improvements to those back reflector designs are necessary, as there is still a significant gap to the Jsc values obtained for cells with a conventionally used thick absorber.