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Rotary printing process for more favorable production of silicon solar cells

The consortium of the Rock-Star research project aims to revolutionize a major process step in Si solar cell production. Particular attention is paid to cost-intensive process steps, such as front and rear metallization. Here, material-saving and throughput-increasing processes can decisively contribute to lowering production costs. This is why: In order to use the electricity generated in the solar cells, it is collected and derived from metal contacts. This task is carried out by the finest contact fingers which are printed on the surface of ultra-thin silicon wafers precisely and without interruption during the front-side metallization with a high throughput.

The conventional flatbed screen printing process reaches its limits here. “Round instead of flat” – that is how the approach of the partners could be described in a shortened manner. They have set themselves the goal of developing and testing new printing processes with which further efficiency gains and productivity increases in the metallization of solar cells can be achieved. As a new technical solution, rotary printing processes such as flexographic printing, rotary screen printing and indirect gravure printing can be considered. Rotary printing processes are mainly used when transferring fine structures with high throughput rates.

In rotary printing, however, the principle is “round to round”. Both the printing form and the counterpressure form have a cylindrical geometry. While paper is subjected to this printing process without damage, the Si solar cells can not be printed between two cylindrical rollers because of the high risk of fracture. Nevertheless, the consortium is faced with the challenge of transferring solar cells to the printing principle “round to flat”. At the same time, printing units and feeders have to work with the utmost precision in order to print the necessary filigree structures with the required accuracy on the silicon wafers. If the research project is successful, a completely new printing process for the metallization will be available to the solar industry. Productivity can be superior to all previous processes.

Graphic (click to enlarge!)

Schematic diagram of the flexographic printing process for the metallization of Si solar cells. (Source: Fraunhofer ISE)