Solar cell achieves record 44.7% efficiency

The breakthrough, made by a team from the Fraunhofer Institute for Solar Energy Systems, in collaboration with Soitec, CEA-Leti and the Helmholtz Center Berlin, was made possible through extensive research into so called III-V multi-junction solar cells and a novel wafer bonding technique. Multi-junction solar cells contain several cells made out of different III-V semiconductor materials stacked on top of each other. The idea is that the single sub cells absorb different wavelength ranges of the solar spectrum. "We are incredibly proud of our team, which has been working now for three years on this four-junction solar cell," said project leader Frank Dimroth. "Besides improved materials and optimisation of the structure, a new procedure called wafer bonding plays a central role. "With this technology, we are able to connect two semiconductor crystals, which otherwise cannot be grown on top of each other with high crystal quality. In this way we can produce the optimal semiconductor combination to create the highest efficiency solar cells."