In the production of silicon solar cells, it is important to have high productivity.

This reduces production costs and eases supply bottlenecks as more and more photovoltaic installations are deployed in Germany and around the world. Led by the Fraunhofer Institute for Solar Energy Systems ISE, a consortium of plant manufacturers, metrology companies and research institutions has come up with a proof of concept for an innovative production line with a throughput of 15,000 to 20,000 wafers per hour to meet this need. This represents double the usual performance and is due to improvements in several individual steps of the process. Detailed results from the research project funded by the Federal Ministry for Economic Affairs and Climate Action (BMWK) will be presented at the eighth World Photovoltaic Energy Conversion Conference this week in Milan, Italy.

“In 2021, 78 percent of all silicon solar cells will be produced in China,” explains Dr. Ralf Prew, Director of the PV Manufacturing Technology Division at Fraunhofer ISE. “To deploy more solar installations as quickly as possible and make our supply chains more stable, Europe needs to rebuild its own production centers for high-efficiency solar cells.” By increasing productivity and making manufacturing technology more resource-efficient, we can significantly reduce costs and unlock the potential for sustainability that we will be able to harness thanks to process knowledge and engineering excellence.”

New concepts for the production of silicon solar cells

The consortium studied each stage of the production of high-efficiency silicon solar cells to optimize the entire process. Several stages of the process require new developments. “For some processes, established production workflows had to be accelerated, other processes had to be reinvented from scratch,” explains Dr. Florian Klement, project leader at Fraunhofer ISE. “Compared to the numbers we see now, the production systems developed under the project achieve at least double the productivity.”

One of the new developments saw the researchers apply new laser equipment in motion which continuously processes the wafers as they move at high speed under the laser scanner. For the metallization of solar cells, the consortium presented rotary screen printing instead of the current standard process, flat screen printing.

Stack diffusion and oxidation

Solar cells require differently doped sections, for example where the silicon layer and metal contacts meet. Fraunhofer ISE researchers integrated the diffusion process used in this context and the thermal oxidation of the wafers in a single process step. Wafers are no longer placed individually, but stacked on top of each other to be processed in the oven. As a result, the oxidation process creates the final doping profile and achieves surface passivation, while at the same time increasing the process performance by a factor of 2.4.

Faster furnace processes

Following the electrode footprint on the solar cells, the contact of the electrodes with the silicon solar cell is formed on both sides in built-in furnaces. Standard furnaces would require a significantly larger heating chamber to increase performance at this stage. Instead, the project consortium installed three times the belt speed in the furnace and compared the quality of the sintered solar cells to today’s standard. They were able to significantly increase performance without compromising the efficiency of the solar cells.

Non-contact testing and defect analysis

To characterize the complete solar cells, the consortium developed two concepts. A non-contact method and a method using sliding contacts were implemented to enable future production lines to test cells more quickly. This makes it possible to maintain a continuous speed of 1.9 meters per second while measuring the cells, with the team demonstrating high measurement accuracy for both concepts. A patent has been filed for the contactless method.

Original article: Encouraging the expansion of photovoltaics by halving the time to produce highly efficient solar cells

Since: Fraunhofer Institute for Solar Energy Systems


Cutting production times for high-efficiency solar cells by half could really speed up adoption

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