Most efficient solar cell

THE Fraunhofer Institute for Solar Energy Systems ISE, Soitec, CEA-Leti and the Helmholtz Centre Berlin have achieved a new world record for the conversion of sunlight into electricity using a new solar cell structure with four solar subcells. They have achieved 44.7 per cent conversion of the solar spectrum’s energy, from ultraviolet through to infrared, into electrical energy.

These solar cells are used in concentrator photovoltaics (CPV), a technology that achieves more than twice the efficiency of conventional PV power plants in sun-rich locations. These so-called III-V multi-junction solar cells contain several cells made out of different III-V semiconductor materials stacked on top of each other. (The Roman numerals refer to groups in the periodic table of elements.) The single subcells absorb different wavelength ranges of the solar spectrum.

“This four-junction solar cell contains our expertise in this area collected over many years,” said Frank Dimroth, Department Head and Project Leader in charge of this development work at Fraunhofer ISE. “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.”

“This world record increasing our efficiency level by more than 1 point in less than four months demonstrates the extreme potential of our four-junction solar cell design which relies on Soitec bonding techniques and expertise,” said André-Jacques Auberton-Hervé, Soitec’s chairman and CEO.

Concentrator modules are produced by Soitec (started in 2005 under the name Concentrix Solar, a spin-off of Fraunhofer ISE). This particularly efficient technology is employed in solar power plants located in sun-rich regions with a high percentage of direct radiation. At present, Soitec has CPV installations in 18 countries, including Italy, France, South Africa and the United States (California).