Fraunhofer ISE in Germany is applying its FlexTrail printing technology to the direct metallization of silicon heterojunction solar cells. It states that the technology reduces the use of silver while maintaining a high level of efficiency.
Researchers at the Fraunhofer Institute for Solar Energy Systems (ISE) in Germany have developed a technique called “FlexTrail Printing,” a method for printing silicon heterojunction (SHJ) solar cells based on silver nanoparticles without a busbar. Front electrode plating method.
“We are currently developing a parallel FlexTrail printhead that can process high-efficiency solar cells quickly, reliably and accurately,” researcher Jörg Schube told pv. “Since fluid consumption is very low, we expect the photovoltaic solution to have a positive impact on cost and environmental impact.”
FlexTrail printing allows for precise application of materials of varying viscosities with extremely precise minimum structure widths.
“It has been shown to provide efficient silver utilization, contact uniformity, and low silver consumption,” the scientists said. “It also has the potential to reduce cycle times per cell due to the simplicity and stability of the process, and hence it is intended for future transfers from the lab.” to factory”.
This method involves the use of a very thin flexible glass capillary filled with liquid at atmospheric pressure up to 11 bar. During the printing process, the capillary is in contact with the substrate and moves continuously along it.
“The flexibility and flexibility of glass capillaries allows for non-destructive processing,” the scientists said, noting that this method also allows curved structures to be printed. “In addition, it balances the possible waviness of the base.”
The research team fabricated single-cell battery modules using SmartWire Connection Technology (SWCT), a multi-wire interconnect technology based on low-temperature solder-coated copper wires.
“Typically, the wires are integrated into the polymer foil and connected to the solar cells using automatic wire drawing. The solder joints are formed in a subsequent lamination process at process temperatures compatible with silicon heterojunctions,” the researchers say.
Using a single capillary, they continuously printed their fingers, resulting in silver-based functional lines with a feature size of 9 µm. They then built SHJ solar cells with an efficiency of 22.8% on M2 wafers and used these cells to make 200mm x 200mm single cell modules.
The panel achieved a power conversion efficiency of 19.67%, an open circuit voltage of 731.5 mV, a short circuit current of 8.83 A, and a duty cycle of 74.4%. By comparison, the screen-printed reference module has an efficiency of 20.78%, an open circuit voltage of 733.5 mV, a short circuit current of 8.91 A, and a duty cycle of 77.7%.
“FlexTrail has advantages over inkjet printers in terms of conversion efficiency. In addition, it has the advantage of being easier and therefore more economical to handle, since each finger only needs to be printed once, and in addition, silver consumption is less. lower, the researchers said, adding that the decline in silver is estimated to be around 68 percent.
They present their findings in the paper “Direct Low Silver Consumption FlexTrail Metallization for Heterojunction Silicon Solar Cells: Evaluating the Performance of Solar Cells and Modules” recently published in the journal Energy Technology.
“In order to pave the way for the industrial application of FlexTrail printing, a parallel print head is currently being developed,” concludes the scientist. “In the near future, it is planned to use it not only for SHD metallization, but also for tandem solar cells, such as the perovskite-silicon tandem.”
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