Friedrich-Alexander-Universität Erlangen-Nürnberg

Fusion Welding of Thin Silicon Substrates

Fusion Welding of Thin Silicon Substrates

Currently, for building up a solar power generation system one has to choose between cost-efficient polycrystalline solar cells with low energy efficiency and expensive monocrystalline solar cells with high energy efficiency. This is one of the reasons why solar power generation is not used in a wide area. Therefore, in order to make solar power generation more appealing the manufacturing costs for solar cells have to decrease and their energy efficiency must increase. To achieve both goals simultaneously, technologies for mass-production of monocrystalline thin film solar cells have to be developed. Well suited for this would be e. g. a roll-to-roll production where monocrystalline, 50 µm thick and thus flexible silicon substrate is provided in large bands.

This process is investigated in a joint research project by the Bayerisches Laserzentrum and the Bayerisches Zentrum für Angewandte Energieforschung. The research topic of the blz is to develop the necessary welding technology to join flexible silicon bands.

Since silicon is brittle and sensitive to strong spatial temperature gradients a line focus is used to heat the joining seam uniformly by the laser. Together with a controlled heating and cool-down phase as well as by homogeneous pre- and post-heating of the joining components a defect free welding seam with minimal warpage shall be realized. Additionally processes are to be investigated that shall reduce surface protrusions of the welding seam due to surface capillary effects.

It was shown that welding joints of thin silicon substrates can be realized. The low material thickness leads to warpage that can not completely be eliminated by a line focus. The residual warpage shall be compensated in further experiments by pre-heating the substrates up to 1000° C in order to achieve joints with the required strength and geometry.

Mechanical stress distribution of a welding seam (cross section)
Characteristics of an overlapping joint welding


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