Researchers at Germany's Fraunhofer Institute for Solar Energy Systems (Fraunhofer ISE) are currently working together with several industrial partners on innovative solutions to drastically reduce silver consumption for silicon heterojunction (HJT) solar cells under the umbrella of a research project funded by the German Federal Ministry for Economic Affairs and Climate Action.
“Within this work, Fraunhofer ISE has investigated several metallization approaches using screen-printed silver-copper and copper pastes on HJT solar cells,” the research project's lead, Andreas Lorenz, told pv magazine. “Our goal is to strongly reduce the silver consumption on the one hand but obtain a high conversion efficiency on the other side by ensuring a very good optical and electrical performance of the screen-printed metallization patterns.”
According to Lorenz, achieving the proposed goal will be possible if very fine lines can be realized particularly on the front cell side using pastes with reduced silver content, with silver being strongly reduced on the rear side, or even completely avoided, by using pure copper paste.
“To realize such fine lines in screen printing, new screen configurations with ultra-fine meshes can be beneficial to realize ultra-fine and uniform contacts,” he added. “We have developed a model to calculate, compare and optimize the effective silver utilization for different screen configurations. It is shown that it can be increased by a factor of 2 when using metallization pastes made of silver and copper with new mesh configurations instead of pure silver pastes.”
Using the Fraunhofer ISE's GridMaster simulation tool, the researchers conducted a series of simulations with different metallization variants to realize high-efficiency solar cells with minimal silver consumption. The experiment showed that conventional metallization with silver paste on the front and back can be gradually replaced by AgCu and pure Cu pastes, and that an ultra-fine line metallization with openings down to 13 μm can be printed using novel ultra-fine mesh screens provided by Japan-based woven wire mesh provider Asada Mesh, Co. Ltd.
“An optimal combination of AgCu paste on the front and pure Cu paste on the back, combined with an optimized fine-line printing process, made it possible to produce highly efficient HJT solar cells with a minimal silver consumption of only 1.4 mg silver per W,” Lorenz explained. “This means that even the long-term goal of a silver consumption of less than 2 mg per W has been successfully demonstrated for the first time.”
The solar cells were also found to achieve even higher efficiency than the silver-metallized reference cells with minimal silver consumption. “The relative increase in efficiency on the silver saving cells with AgCu and Cu metallization is 0.9%,” Fraunhofer ISE researcher, Sebastian Pingel, said. “We achieved this result when we printed finer lines with an opening of 17 µm instead of 20 µm opening on the front side with AgCu instead of Ag and Cu instead of Ag on the rear side.”
“Unfortunately, we have not calculated this for the specific cells,” Lorenza said, when asked about potential improvements in manufacturing costs. “It would be possible to do this, but it is not so easy as the whole production process has to be considered for a solid COO analysis. However, the cost-saving potential is substantial, as the cost for the silver metallization does make a significant share of the total costs.”
“Further activities at Fraunhofer ISE will focus on further reducing the printed finger width and evaluating the reliability and long-term stability of the novel metallization in the module,” he concluded.
Recently, the same research team also demonstrated how to reduce silver consumption for HJT cells by screen printing using low-temperature paste based on Ag, Ag-coated Cu or pure Cu particles. Their findings are available in the paper “Transition from silver-to copper-based screen printed SHJ solar cells,” which was recently published in Solar Energy Materials and Solar Cells.
This content is protected by copyright and may not be reused. If you want to cooperate with us and would like to reuse some of our content, please contact: editors@pv-magazine.com.
By submitting this form you agree to pv magazine using your data for the purposes of publishing your comment.
Your personal data will only be disclosed or otherwise transmitted to third parties for the purposes of spam filtering or if this is necessary for technical maintenance of the website. Any other transfer to third parties will not take place unless this is justified on the basis of applicable data protection regulations or if pv magazine is legally obliged to do so.
You may revoke this consent at any time with effect for the future, in which case your personal data will be deleted immediately. Otherwise, your data will be deleted if pv magazine has processed your request or the purpose of data storage is fulfilled.
Further information on data privacy can be found in our Data Protection Policy.