Solvent-free PV coating system allows contactless application

Competitiveness of photovoltaic modules requires higher efficiency at lower costs. To maximize both, contacting of crystalline solar cells is done by way of the back surface. The aluminium layer usually applied to the back surface of the wafer by the physical vapour deposition (PVD) process results in excellent electrical conductivity. However, the problem has been application of the busbars, because the traditional procedure 锟? silk-screen printing of solderable silver pastes 锟? cannot be used due to lack of adhesion. Plus, additional thermal stress arising when burning off the binder can have an adverse effect on silicon wafer quality. This is where plasmadust technology developed by Reinhausen Plasma comes into play.

To deliver solderable layers with maximum adhesion, it is now possible to use dry, solvent-free coating process to deposit various solderable metal alloys as micropowders or nanopowders directly onto the aluminium layer from a cold, active plasma at atmospheric pressure. Meanwhile, the PVD contact layer is neither damaged nor contaminated by the coating process.

Cost optimization with alternative coating materials: Powders of copper and tin as well as silver alloys are now available as coating materials for the application of busbars. Compared to conventional silver pastes, this means cost savings since considerably less silver or none is required in the plasmadust process. Copper, in particular, provides greater wettability and adhesive strength at lower costs. Tin, as the most cost-effective alternative, also gives impressive results.

The plasmadust process is also available as an alternative if the entire back surface of the cell is to be metallized. The deposition of an aluminium layer between 10 and 20 锟絤 thick is carried out at high process speeds. As a result, significantly less energy is used in this process than in conventional processes. For example, only around 1/10 to 1/100 of the energy required for thermal spray processes is needed to metallize an area of one square meter. Additionally, the plasmasun system is designed for a throughput of up to 2,400 wafers/hour.

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