A steady increase in new photovoltaic installations and thus a rising contribution of solar energy to the world-wide energy production can only be ensured by a continuous reduction of the $/Watt costs for photovoltaic systems. Silicon single-junction solar cells are close to reaching their practical efficiency limit which will boost the need for higher-efficient photovoltaic technologies. Efficiencies over 30% were demonstrated by combining Si solar cells with wide-bandgap III-V top cells. Despite these impressive efficiencies, the application of solar cells including III-V semiconductors has been limited by the high fabrication costs mainly caused by the MOCVD growth and required substrates. Other, potentially lower-cost top cell materials like perovskite semiconductors have so far not been able to reach tandem cell efficiencies of 30%. The costs of III-V top solar cells can be drastically reduced when using GaAs nanowire arrays fabricated by Aerotaxy™. Due to the superior geometry, high theoretical single-junction efficiencies of >25% can be achieved for an area coverage of <20%, enabling tandem cell efficiencies over 30% when applied in a tandem cell with Si bottom cell. The fabrication by Aerotaxy™  does not require a growth substrate, allows an efficient use of the precursors and is conducted at higher throughputs. In this presentation, more insights into the concept of low-cost GaAs nanowire/Si tandem solar cells will be given and the great potential of this innovative technology will be discussed.
 M. Heurlin, M. H. Magnusson, D. Lindgren, M. Ek, L. R. Wallenberg, K. Deppert, L. Samuelson,
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