Fabrication of Highly Efficient Four-Junction Solar Cells by Surface-Activated Wafer-Bonding

We used surface-activated wafer-bonding (SAB) at low temperatures for the fabrication of advanced four-junction solar cells. The bonded heterojunctions are optimized regarding high electrical conductivity to avoid voltage losses especially for devices operating with high-current densities. Wafer-bonded 4-junction solar cells are today reaching the highest efficiencies for sunlight conversion into electricity and offer possible applications for space as well as concentrating photovoltaics.