Development of coplanar back contact for large area, thin, GaAs/Ge solar cells

The development of large-area (⩾6×6 cm), thin (<6 mils), high-efficiency GaAs solar cells on Ge substrates with coplanar back contacts is discussed. Over 300 solar cells have been fabricated to date, to identify process issues and to demonstrate a production capability. Key process areas of concern were edge rounding and deposition of high-quality continuous dielectric layers around the cell edges. Several edge rounding techniques and various dielectric deposition techniques were evaluated to identify the best dielectric system. Using improved dielectric layers and edge rounding techniques, large-area (6×6 cm), wraparound GaAs/Ge solar cells with an AMO efficiency up to 17.4% have been obtained. Smaller-area (4×4 cm) wrapthrough GaAs/Ge solar cells showed an AMO efficiency of 18.0%