LONDON Belgian research organization IMEC is claiming a major breakthrough in solar cell conversion efficiency using GaAs solar cells on germanium substrates.
IMEC (Leuven, Belgium) says it has achieved a record 24.7 percent conversion rate on a single-junction GaAs solar cell on a Ge substrate.
The cell was made under the ESA-IMAGER project. Materials technology group Umicore (Brussels, Belgium) produced the Ge substrate through an optimized manufacturing technology, aimed at improving the intrinsic germanium crystal quality.
The efficiency was measured and confirmed by NREL (National Renewable Energy Laboratory, US). GaAs solar cells are used in satellite solar panels and earth-based solar concentrators.
The cell was grown at the research group epitaxially on a Ge substrate with what it says is an improved micro-defect distribution to what has been possible to date. The cell measures 0.25cm², and the 24.7 percent efficiency was achieved using an open-circuit voltage (Voc) of 999 mV, a short-circuit current (Jsc) of 29.7 mA/cm², and a fill factor of 83.2 percent.
The researchers say improving the efficiency of single-junction GaAs cells is a major step in the development of a hybrid monolithic/mechanically stacked triple-junction solar cell. This type of solar cells 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 focuses on stacked cells consisting of top cells with III-V materials and bottom cells made from Ge. With this combination, IMEC is targeting conversion efficiencies above 35 percent.