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Spanish institute's III-V cell hits 39.2 percent

The cell has a GaInP based top cell, a GaInAs based middle cell and a germanium bottom cell and was grown on a germanium substrate
The Group of III-V Semiconductors of the Solar Energy Institute of the Technical University of Madrid (IES-UPM) in Spain has grown a concentrator solar cell with an efficiency of 39.2 percent.

This was confirmed by the Fraunhofer Institute for Solar Energy Systems in Freiburg, Germany.

In 2008, IES-UPM developed a dual junction III-V solar cell with an efficiency of 32.6 percent at 1026 suns - a world record at that time. Since then, the research group has focused its attention on manufacturing lattice-matched triple junction solar cells for ultra high concentration (1000 suns and above).

The devices have an active area of 1 mm2 and consist of a GaInP based top cell (TC) of ~ 1.9 eV, a GaInAs based middle cell (MC) of ~ 1.4 eV and a germanium bottom cell (BC) of ~ 0.6 eV grown on germanium substrates.

The concentration performance of the cell as measured at Fraunhofer ISE is shown in the figure below.

The measured cell shows a peak efficiency of 39.2 percent at a concentration of 398 suns, while the efficiency is still higher than 37 percent at 1000 suns.

The cell was grown by MOCVD at IES-UPM's facilities and the semiconductor structure includes a high band gap GaInP/AlGaAs tunnel junction between the TC and MC. This tunnel junction is able to operate at concentrations higher than 15000 suns. The TC also incorporates disordered GaInP, induced by the use of antimony during the epitaxial growth of the TC.

The whole cell is now being carefully optimised by using proprietary software and, in the near future, efficiencies higher than 42 percent are expected to be achieved at concentrations of 1000 suns.

The operation at 1000 suns or higher irradiances have been traditionally a goal for the Group of III-V Semiconductors of IES-UPM in order to achieve competitive electricity prices, well below those of 500 suns operation.

Besides, a good performance of the cells at concentrations higher than 1000 suns is highly recommended in order to prevent the detrimental effects of the unavoidable non-uniformity of light impinging the solar cell in optical concentrators.


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