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IMEC touts record GaAs solar cells conversion efficiency of 24.7% on Ge substrate
The cell was made under the ESA-IMAGER project, with materials technology group Umicore producing the Ge substrate through an optimized manufacturing technology, aimed at improving the intrinsic germanium crystal quality, IMEC noted.
By Ann Steffora Mutschler, Senior Editor -- Electronic News, 2/25/2008
Leuven, Belgium-based nanoelectronics and nanotechnology research center IMEC announced today that it has achieved a conversion efficiency of 24.7% for a single-junction GaAs solar cell on a Ge substrate, which has been measured and confirmed by the National Renewable Energy Laboratory.
GaAs solar cells are used in satellite solar panels and earth-based solar concentrators, IMEC noted, and said this result is a record on a single-junction GaAs cell, grown epitaxially on a Ge substrate with an improved micro-defect distribution.
The record cell measures 0.25-square centimeters, and shows an efficiency of 24.7%, with an open-circuit voltage of 999mV, a short-circuit current of 29.7 square mA/cm and a fill factor of 83.2%.
The cell was made under the ESA-IMAGER project, with materials technology group Umicore producing the Ge substrate through an optimized manufacturing technology, aimed at improving the intrinsic germanium crystal quality.
IMEC said improving the efficiency of this single-junction GaAs cell is another step towards the development of a hybrid monolithic/mechanically stacked triple-junction solar cell, which consists of stacks of solar cells made of different semiconductors, carefully chosen to absorb the solar spectrum as efficiently as possible.
Among the many possible combinations, IMEC said it focuses on stacked cells consisting of top cells with III-V materials and bottom cells made from Ge, and with this combination, is targeting a conversion efficiency of 35% and higher, with the resulting stacks able to be used in satellites and earth-based concentrators, where high-efficiency energy conversion is paramount.
In other solar-related news, Lausanne, Switzerland-based water jet-guided laser technology company Synova said today it has joined a research alliance led by Europe's largest solar research organization, the Fraunhofer Institute for Solar Energy Systems (ISE), to explore new manufacturing methods that will both speed processing and improve the performance of solar cells.
The alliance, comprised of industry leaders whose offerings span the photovoltaic manufacturing spectrum from raw materials to finished cells, is investigating the use of Synova's Laser MicroJet (LMJ) technology with liquids other than pure water to prove LMJ's viability for wafering and microstructuring applications.
Specifically, the alliance said it is exploring LMJ for laser chemical processing, an approach that extends beyond laser chemical etching to other processes, first published by ISE in 2001 at the European Photovoltaic Solar Energy Conference in Munich.
Through this research effort, the alliance members expect to produce a superior alternative to conventional lasers, chemical processes, diamond blade saws and multi-wire slurry saws, aimed to increase solar cell efficiency while lowering overall cell cost.
While conventional lasers have yielded the most promising results for these processes to date, Synova said its LMJ can take these benefits even further due to its "wet" approach offers improved cell integrity by eliminating heat and silicon surface damage, as well as contamination from the process debris associated with "dry" lasers.
