The Fraunhofer Institute for Solar Energy Systems ISE, Soitec, CEA-Leti and the Helmholtz Centre Berlin have announced the achievement of a new world record for the conversion of sunlight into electricity using a new solar cell structure with four solar sub-cells. After three years of research, an efficiency of 44.7% was measured at a concentration of 297 suns. This indicates that 44.7% of the solar spectrum’s energy, from ultraviolet through to the infrared, is converted into electrical energy.
This is considered to be a major step towards reducing further the costs of solar electricity and continues to pave the way to the 50% efficiency target.
In May this year, the same German-French team announced a solar cell with 43.6% efficiency. The new mark results, it says, from further intensive research work and optimisation.

These solar cells are used in concentrator photovoltaics (CPV), a technology which achieves more than twice the efficiency of conventional PV power plants in sun-rich locations. The use on land of the so-called III-V multi-junction solar cells, which originally came from space technology, has proved to realise the highest efficiencies for the conversion of sunlight to electricity. In this multi-junction solar cell, several cells made out of different III-V semiconductor materials are stacked on top of each other, so that single sub-cells absorb different wavelength ranges of the solar spectrum. The team has been working on a four-layer version.
"We are incredibly proud of our team which has been working now for three years on this four-junction solar cell," says Frank Dimroth, department head and project leader in charge of this development work at Fraunhofer ISE. "This four-junction solar cell contains our collected expertise in this area over many years. 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 4 months, demonstrates the extreme potential of our four-junction solar cell design which relies on Soitec bonding techniques and expertise," says AndrĂ©-Jacques Auberton-HervĂ©, Soitec’s chairman and CEO. "This new record value reinforces the credibility of the direct semiconductor bonding approaches that is developed in the frame of our collaboration with Soitec and Fraunhofer ISE." said Leti CEO Laurent Malier.

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