January 27, 2009 Researchers at the Fraunhofer Institute for Solar Energy Systems ISE have set a new record for solar cell efficiency. Using concentrated sunlight on a specially constructed multi-junction solar cell, the research group lead by Frank Dimroth has achieved 41.1% efficiency for the conversion of sunlight into electricity.

The breakthrough, which surpasses the 40.7 percent efficiency previously demonstrated by Spectrolab , involved the use of sunlight concentrated by a factor of 454 and focused onto a small 5 mm multi-junction solar cell made out of GaInP/GaInAs/ Ge (gallium indium phosphide, gallium indium arsenide on a germanium substrate). Even at a higher sunlight concentration of 880, an efficiency of 40.4% was measured.

"We are elated by this breakthrough," says Frank Dimroth, head of the group "III-V - Epitaxy and Solar Cells" 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."

Multi-junction solar cells combine semiconductor compounds in layers to absorb almost all of the solar spectrum. The problem is that in combining these materials in a process known as metamorphic growth, defects occur in the lattice structure making it difficult to grow the III-V semiconductor layers with a high crystal quality. The Fraunhofer ISE researchers have overcome this issue by discovering a way to localize these defects in a region of the solar cell that is not electrically active, meaning that the active regions stay relatively defect free and higher efficiencies can be achieved.

"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!"

Via: Fraunhofer Institute for Solar Energy Systems ISE (http://www.ise.fraunhofer.de/)