Credit: Fraunhofer ISE

from phys.org: German Fraunhofer Institute for Solar Energy Systems, Soitec,
CEA-Leti and the Helmholtz Center Berlin announced today that they have
achieved a new world record for the conversion of sunlight into
electricity using a new solar cell structure with four solar subcells.
Surpassing competition after only over three years of research, and
entering the roadmap at world class level, a new record 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 a major step
towards reducing further the costs of solar electricity and continues to
pave the way to the 50% efficiency roadmap.


Back in May 2013, the German-French team of Fraunhofer ISE,
Soitec, CEA-Leti and the Helmholtz Center Berlin had already announced a
solar cell with 43.6% efficiency. Building on this result, further
intensive research work and optimization steps led to the present
efficiency of 44.7%.



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 terrestrial use
of so-called III-V multi-junction solar cells, which originally came
from space technology, has prevailed to realize 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. The single subcells 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,” 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
optimization 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 André-Jacques Auberton-Hervé, Soitec’s Chairman and CEO. “It
confirms the acceleration of the roadmap towards higher efficiencies
which represents a key contributor to competitiveness of our own CPV
systems. We are very proud of this achievement, a demonstration of a
very successful collaboration.” 

“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. We are very proud of this
new result, confirming the broad path that exists in solar technologies
for advanced III-V semiconductor processing,” said Leti CEO Laurent
Malier.

Source: Phys.org