Researchers at Germany’s Fraunhofer Institute for Solar Energy Systems (Fraunhofer ISE) have used oblique gravure printing for the front-side metallization of silicon heterojunction (SHJ) photo voltaic cells, decreasing silver consumption. with cycle instances of 0.5 seconds per cell, and obtain excessive conversion effectivity. to twenty.7%.
“A serious benefit of rotary printing methods, resembling gravure printing but in addition rotary display screen printing and flexographic printing, is the flexibility to drastically cut back the cycle time per wafer and, thus, enhance the throughput per hour in comparison with the state-of -the-art metallization strategies,” stated analysis chief Jörg Schube pv journal.
The researchers famous that the effectivity outcomes have been decrease by 1.7% in comparison with the screen-printed reference however the cycle time was diminished.
The aim of the analysis is to seek out higher silicon photo voltaic cell metallization methods in mild of PV industrial expertise roadmapwhich may see extra silicon heterojunction (SHJ) cells and silicon-based tandem gadgets forward.
The aim can be to develop low-temperature metallization processes that use much less silver, but in addition function at excessive ranges of throughput. For instance, the researchers famous that the throughput ought to enhance from 4,000 wafers per hour per lane to 9,500 wafers per hour per lane, which corresponds to cycle instances of 0.9 seconds and 0.5 seconds per cell, respectively.
Such constraints level to a metallization method based mostly on applied sciences, resembling parallel dishing out, inkjet printing, rotary printing, or FlexTrail, based on researchers. FlexTrail is a brand new printing expertise developed by Fraunhofer ISE.
The Fraunhofer ISE staff determined to concentrate on a rotary printing method referred to as oblique gravure printing – a expertise utilized in excessive quantity, top quality journal and catalog printing or within the packaging business.
The staff used industrial SHJ precursors for the experiment and the again facet display screen printing of fingers. Indirect gravure printing was utilized to the entrance facet of the pattern utilizing gravure widths of fifty μm and 80 μm. Besides gravure width, switch cylinder inking functions range in quantity. A reference display screen printed machine can be ready.
All samples have been then annealed, laser reduce, and mechanically reduce into half cells, adopted by IV and electroluminescence testing, busbar printing, and drying steps. Characterization contains confocal microscopy, scanning electron microscope (SEM) and four-point probe measurements.
Samples produced utilizing the champion oblique gravure printing course of had a imply width of 65 μm and a imply finger top of 5 μm. When used for entrance metallization, SHJ photo voltaic cells have a conversion effectivity of as much as 20.7%, which is 1.7% [absolute] decrease than the reference entrance facet, screen-printed photo voltaic cells, however the cycle time is diminished, emphasised the staff.
The staff famous that to one of the best of its data, “that is the very best effectivity SHJ photo voltaic cells that includes gravure-printed metallization reported thus far.” It added that even with out optimization, the champion’s oblique gravure printing course of “can meet the necessity for elevated throughput,” and doubtlessly cut back PV manufacturing prices.
Schube stated the staff was stunned at how shortly it may obtain a “vital” size of printed steel contacts when beginning to use oblique gravure printing. “Using an acceptable manufacturing platform permits cycle instances of 0.5 seconds per cell, and even decrease. This high-throughput potential along with the sturdiness of gravure sleeves can result in a terrific benefit of this printing method over state-of-the-art metallization strategies,” he defined.
In the next photo voltaic cell simulations, the researchers discovered that with out further course of optimization, oblique gravure printing can be utilized because the again metallization for SHJ photo voltaic cells with solely a 0.1% loss in conversion effectivity in comparison with in display screen printing.
However, the researchers notice that there’s room for enchancment on this variant of rotary printing. Specifically, they point out the finger resistance and get in touch with resistance on the contact/indium tin oxide interface might be diminished by “adjusting the ink formulation and annealing circumstances”. In addition, they famous that higher machine alignment can enhance the homogeneity of the contact fingers, and the optimized gravure design can cut back the finger width, whereas conserving the finger top at 5 μm or extra.
The staff acknowledged that though they experimented with SHJ gadgets, the outcomes could possibly be transferred to different high-efficiency wafer-based cell ideas that require low-temperature metallization, resembling gadgets that tandem of silicon perovskite.
The analysis staff contains scientists from the Continental Center for Functional Printing Technologies (CFPT), an R&D unit of automotive business provider Continental, and gravure producer Sächsische Walzengravur (SWG).
Its work is described in “High-throughput oblique gravure printing utilized in low-temperature metallization of silicon-based high-efficiency photo voltaic cells,” revealed in Energy Technology. “The revealed outcomes are very encouraging for the entire staff to proceed creating this new technique of metallization. The subsequent steps are to cut back the width of the printed contacts and to optimize the design of the steel grid format ,” Schube stated wanting forward.
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