!!! Press Release !!! GaAs Single Junction Solar Cell at 24
% Conversion Efficiency European record for GaAs single junction solar cell grown on AIX 2400/2600 G3 The Fraunhofer Institute for Solar Energy Systems (ISE) has started their MOCVD activities towards the growth of solar cell structures in 1997. The AIX 2400/2600 G3 MOCVD system was their choice due to the high flexibility of the system and the superior performance of the AIXTRON Planetary ReactorsÒ for the mass production of GaAs single junction solar cells and GaAs/GaInP tandem solar cells worldwide. Fraunhofer ISE has now been successful in growing GaAs single junction solar cells with extremely high conversion efficiency. The solar cell structure consists of an active GaAs single junction solar cell grown on an inactive backside AlGaAs/GaAs DBR using GaAs substrate. It is capped with an AlGaAs window. The reflectivity of the backside DBR is approximately 70 % for light with energy close to the bandedge of GaAs. The cell is coated with a TiO2/MgF2 anti reflection coating. Measurements were performed at the photovoltaic calibration laboratory of Fraunhofer ISE. Calibration was done at one sun AM1.5g and AM0. The conversion efficiency is 24,2 % at AM1.5g and 22 % at AM0. Both values are known as the best values for GaAs single junction cells achieved in Europe. These values are close to the best worldwide. GaAs based solar cells are preferred for powering of space satellites. The use of Ge substrates reduces weight significantly, the conversion efficiency can be further increased by using GaInP/GaAs tandem solar cells. These types of solar cells are superior to Si cells due to their lower weight and their higher resistance to the cosmic radiation. Fraunhofer ISE plans to further develop their processes towards the production of GaInP/GaAs tandem solar cells grown on Ge substrates. They also intend to use such high efficiency solar cells for terrestrial applications. This may require the use of concentrator systems with concentrations of 300 to 1000 suns. For further information please contact:
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