silicon wafers molding for photovoltaïc application – MOSAIQUE

The aim of the MOSAIQUE project is to propose a novel solution for the processing of PV silicon based on the directional crystallization of Si sheets molded in parallel.
In comparison with the current method of slicing bulk Si lingots prepared by directional crystallization, the proposed method allows avoiding the additional costs and material losses caused by the cutting step. And, in comparison with the ribbon pulling methods studied up to now, the new method should give a better Si microstructure while keeping a high productivity. Moreover the new method can be operated in the existing industrial crystallization furnaces and does not imply heavy investments, in contrast with the ribbon technologies.
The first part of the project is devoted to the development of a mould material with the associated coating that must lead to a spontaneous detachment of silicon during cooling. This development will be based on an experimental study of wetting and adhesion of silicon on the coated mould. The results of this study will be used to develop a molding process at the scale of the laboratory. This consists in the control of : the infiltration of the mould by molten silicon, the heterogeneous nucleation of silicon at the mould walls, the surface shape and final microstructure of solidified Si as well as the pollution of silicon caused by the mould. The optimal parameters determined by this study will be used to process silicon sheets that will be tested as PV cell base material. From the measured cell efficiencies, the potentialities of the molding process will be evaluated.
The proposed project is an industrial collaborative research. It will be conducted using the basic knowledge of the three laboratories taking part into this project, specialized in the respective fields of wetting and adhesion, nucleation, crystal growth and segregation, and diffusion /precipitation of impurities in solid silicon in relation with electrical properties. The application of the process will rely on the experience and contribution of two industrial societies, the first being implied in the development of the mould material, and the second in the development of the molding furnace.