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The Fraunhofer Institute for Solar Energy Systems (ISE) has claimed another major breakthrough in solar cell efficiencies via its successful development of metamorphic crystal growth processes using triple junction cells. The cell is fabricated using GaInP/GaInAs/Ge (gallium indium phosphide, gallium indium arsenide on a germanium substrate) that has produced record conversion efficiencies of 41.1% with a 454 concentration factor.
“We are elated by this breakthrough,” says Frank Dimroth, head of the 'III-V – Epitaxy and Solar Cells' group at Fraunhofer ISE. “At all times the entire team believed in our concept of the metamorphic triple-junction solar cells and our success today is made possible only through their committed work over the past years.”
Employing a metamorphic crystal growth process has proved elusive due to the lattice differences created in the cell creating dislocations and a range of defects, rendering poor results.
The Fraunhofer researchers have worked on localizing the defects in a region of the solar cell that is not electrically active. The active regions retain only limited defects and therefore can produce electricity at good efficiency levels due to the favourable conversion rates when using the III-V materials selected.
“This is an especially good example of how the control of crystal defects in semiconductors can lead to a breakthrough in technology,” noted Prof. Eicke R. Weber, Director of Fraunhofer ISE.
The success of the metamorphic crystal growth processes is expected to lead to a wider range of light absorbing III-V materials being selected for multi-junction solar cells, boosting cell efficiencies further. Efforts are expected to focus on the matching efficiency levels within the three sub-cell areas as currently the lowest efficiency cell dictates current output.
“The high efficiencies of our solar cells are the most effective way to reduce the electricity generation costs for concentrating PV systems,” says Dr. Andreas Bett, Department Head at Fraunhofer ISE. “We want that photovoltaics becomes competitive with conventional methods of electricity production as soon as possible. With our new efficiency results, we have moved a big step further towards achieving this goal!”
The research team at Fraunhofer ISE celebrates its success in reaching a new world record efficiency with the Institute Director Prof. Eicke Weber (centre), Dept. Head Dr. Andreas Bett (left) and the Group Leader Dr. Frank Dimroth (right).