Development of multi-junctions high efficiency solar cells on reclaimable substrates – SolarBond

The overall Photovoltaic (PV) industry grows by more than 30 % per year and the market volume is expected to reach over 20 billion Euros in 2010. Most of the technology in the field is based on silicon solar cells today. On the other hand, III-V multi-junction solar cells are reaching significantly higher solar to electric conversion efficiencies exceeding 40 %. These solar cells are widely used for powering satellites and recently also the promising terrestrial market of concentrator PV is starting to grow rapidly. These systems make use of the highest efficiency III-V multi-junction solar cells under an optical concentrator such as a Fresnel lens, concentrating the sunlight by a factor of 500-1000. In this way the area of expensive III-V semiconductor material is greatly reduced by the use of cheaper optical elements. Still, the solar cell accounts for approximately 20 % of the system costs.Therefore, reducing the cost of the multi-junction solar cell as well as increasing their conversion efficiency are important strategies for achieving the goal of making this technology competitive to conventional energy sources in the future. In the project “SolarBond”, we are aiming to develop and demonstrate a new alternative substrate technology which allows growing high-efficiency GaAs based solar cells with excellent crystal quality and to remove the substrate afterwards in a simple lift off process. To achieve this, the alternative substrate will provide a thin monocrystalline layer,i.e. an epitaxial template for the solar cell, on top of a temporary handle substrate. In between, a buried lift off layer will be incorporated allowing removing the solar cell after its growth from the substrate. Both the initial substrate, providing the thin monocrystalline layer, and temporary handle will be recycled, thus saving expensive material and allowing reducing the substrate cost.