New production process could double wafer throughput to 20,000 per hour – pv magazine International

September 28, 2022 Beatrice Santos

A group of plant manufacturers, metrology companies and research institutes led by the German Fraunhofer Institute for Solar Energy Systems (Fraunhofer ISE) have optimized several steps in the silicon solar cell production process, which translates to a throughput of 15,000 to 20,000 platelets per hour – about double the usual amount.

One of the innovations concerns the integration of the diffusion process, combining solar doping and thermal oxidation of wafers in a single step. Thermal oxidation of wafers is usually carried out in furnaces, with the wafers being transported through the furnace in so-called quartz rack boats. Wafers are usually placed individually in these boats, but the researchers optimized the process by stacking the wafers on top of each other in special quartz boats. The resulting oxidation process creates the final doping profile and simultaneously achieves surface passivation, increasing process throughput by a factor of 2.4.

In the next stage of the process, the contact with the electrodes printed on both sides of the silicon solar cells is formed in inline ovens. To increase throughput at this point, the researchers installed a significantly faster belt speed in the oven, bypassing the standard need for a much larger heating chamber. The group compared the quality of sintered solar cells with the current standard and found that the throughput increased significantly without compromising the efficiency of the solar cells.

While processes like these were accelerated, others “had to be reinvented from scratch,” said Florian Clement, project manager at Fraunhofer ISE. In one of the new developments, the researchers implemented new on-the-fly laser equipment that continuously processes wafers as they move at high speed under the laser scanner. For the metallization of solar cells, the consortium introduced rotary screen printing instead of flat screen printing, the current standard process. This technique could significantly reduce the amount of money needed to produce solar cells, while maintaining high levels of power conversion efficiency.

Finally, the researchers devised two new concepts to speed up the testing of cells by future production lines: a contactless method and a method using sliding contacts. Cells can be measured accurately at a continuous speed of 1.9 meters per second with the new methods. The team filed a patent for the contactless method.

The consortium is presenting the detailed results of the research project this week at the World Photovoltaic Energy Conversion Conference in Milan, Italy. China still produces most silicon solar cells in the world – up to 78% in 2021 – so the group sees the project’s results as a way to make European factories more competitive.

“In order to deploy more solar installations as quickly as possible and to make our supply chains more robust, Europe should re-establish its own production centers for high-efficiency solar cells,” said Ralf Preu, Division Director of PV production technology at Fraunhofer. ISE. “By increasing throughput and making production technology more resource-efficient, we can significantly reduce costs and unlock the potential for sustainability that we can tap into through process knowledge and engineering excellence.”