High-throughput Si foil technologies at Fraunhofer ISE

Cost reduction is still the driving force in photovoltaic industry. One promising way to tackle this issue in the crystalline silicon technology is to reduce the consumption of highly purified Si raw materials. To avoid kerf losses and to manufacture still high quality Si foils with thicknesses in the range of 50 μm the porous Si approach [1, 2] is one potential solution. Several investigations could show that although Si is an indirect semiconductor such thin layers are sufficient for conversion efficiencies well above 20 % [3] given good material quality and optical confinement. At Fraunhofer ISE we have been working on high-throughput solutions for all necessary technologies such as porosification, reorganization plus Si epitaxy and lift-off. In this paper we will present the first reliable process to produce Si foils with reorganization and epitaxial thickening done in an industrially relevant inline tool. The paper will furthermore give a status report on the different technology steps.