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BASF and Schmid have jointly developed a contact-free, laser-transfer printing (LTP) process for metallising the front and back of solar cells.

The printer and paste system is based on a contact-free laser process and offers customers advantages with regard to handling, as well as increasing the efficiency of cell production.

They contain no lead and the silver and aluminum pastes are available as solvent-free, water-based products.

The LTP PV 1500 laser transfer printer was developed by the Schmid Group to replace the existing screen printing process.

It can be used for coating both the backs of solar cells with aluminum and aluminum/silver and the fronts with silver.

The system can be integrated into existing production lines and is suitable for all types and sizes of cells.

There are plans for technical interlinking for combined printing of fronts and backs.

The LTP printer achieves a throughput of 1500 wafers per hour and works without any contact to prevent mechanical stress on the wafers.

A wafer for printing is pre-positioned, held in place on a vacuum conveyor and then passed through under the laser.

The laser beam separates the metallisation paste from the carrier film and transfers the paste to the wafer.

The paste on the film is constantly replaced in a cycle.

An integrated ink supply with viscosity control ensures that pastes with different compositions can be used.

Because the printing is done digitally, any patterns can be printed and serialisation of the individual printed wafers is possible.

From 2010, BASF will be offering customised metallisation pastes for mono- and multicrystalline solar cells that are designed specifically for the LTP process and can also be used in conventional screen printing.

The portfolio will comprise silver pastes for front-side printing and aluminum-based pastes for printing of back sides.

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