Scientists grow PV crystals with record efficiency
According to a release from Fraunhofer Institute for Solar Energy Systems (Fraunhofer ISE) The basis for the high efficiency is a specific technique to grow the semiconductor material for the solar cells. The cells are made of III-V-material on GaAs or Ge substrates. The technique of 'amorphous multiple cells' developed by the institute avoids the formation of impurity traps which normally emerge where in the transition zone of materials with different lattice constants. The Fraunhofer experts say they succeeded in concentrating these defects within an electrically inactive area of the solar cell. The active areas however remain largely defect-free which in turn is a condition to achieve high efficiencies. "This is a good example how the control over crystal defects within semiconducting materials can cause a technological breakthrough", said institute manager Eicke Weber.
The efficiency of 41.4 percent was achieved in an experiment in which the light was concentrated by a factor of 454 and directed to what the scientists called a multiple solar cell which covered an area of 5 square millimeters.
Besides the 'amorphous multiple cell' technique the scientists chose a material composition that created a spectral sensitivity distribution very similar to the spectral distribution of sunlight. This was another criterion for the high efficiency.
In order to bring the technique to market as fast as possible and to improve its competiveness against conventional generators, Fraunhofer ISE collaborates with Azur Space (Heilbronn, Germany) and Concentrix Solar GmbH (Freiburg).
Andreas Bett, department director at Fraunhofer ISE, pointed to the connection between solar cell efficiency and power costs. "The high efficiency of our solar cells is the most effective way to reduce the energy costs for this type of photovoltaic systems," he said. "Our aim is to achieve competiveness of photovoltaics against conventional ways to generate electrical energy."
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