Researchers at Germany’s Fraunhofer Institute for Photo voltaic Vitality Techniques (Fraunhofer ISE) have used oblique gravure printing for front-side metallization of silicon heterojunction (SHJ) photo voltaic cells, decreasing silver consumption at cycle instances of 0.5 seconds per cell, and attaining conversion efficiencies of as much as 20.7%.
“A serious good thing about rotary printing methods, corresponding to gravure printing but additionally rotary display screen printing and flexographic printing, is the flexibility to strongly cut back cycle time per wafer and, thus, improve throughput per hour in comparison with state-of-the-art metallization strategies,” analysis chief, Jörg Schube, informed pv journal.
The researchers famous that the effectivity outcomes had been decrease by 1.7% in comparison with the screen-printed reference however the cycle time was diminished.
The purpose of the analysis is to seek out higher silicon photo voltaic cell metallization methods in mild of the PV business’s expertise roadmap, which sees extra silicon heterojunction (SHJ) cells and silicon-based tandem gadgets forward.
The purpose can also be to develop low-temperature metallization processes that use much less silver, but additionally function at excessive throughput ranges. For instance, the researchers famous that the throughput should improve 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 approach primarily based on applied sciences, corresponding to parallel allotting, inkjet printing, rotary printing, or FlexTrail, mentioned the researchers. FlexTrail is a novel printing expertise developed by Fraunhofer ISE.
The Fraunhofer ISE workforce determined to give attention to a rotary printing approach often known as oblique gravure printing – a expertise utilized in high-volume, high-quality journal and catalog printing or within the packaging business.
The workforce used industrial SHJ precursors for the experiment and rear facet display screen printing of fingers. The oblique gravure printing was utilized to the samples’ entrance facet utilizing gravure widths of fifty μm and 80 μm. In addition to gravure width, the variety of inking purposes on the switch cylinder was assorted. A reference display screen printed gadget was additionally ready.
All samples had been then annealed, laser reduce, and mechanically cleaved into half cells, adopted by IV and electroluminescence testing, busbar printing, and drying steps. Characterization included confocal microscopy, scanning electron microscope (SEM) and four-point probe measurements.
The samples made with the champion oblique gravure printing course of had a imply width of 65 μm and a imply finger peak of 5 μm. When utilized for entrance metallization, the SHJ photo voltaic cells had conversion efficiencies of as much as 20.7%, which is 1.7% [absolute] lower than the reference entrance facet, screen-printed photo voltaic cells, however the cycle time was diminished, harassed the workforce.
The workforce famous that to the very best of its information, “these are the highest-efficient SHJ photo voltaic cells that includes gravure-printed metallization reported to date.” It added that even with out optimization, the champion oblique gravure printing course of “can meet the demand for growing throughput,” and doubtlessly cut back prices in PV manufacturing.
Schube mentioned the workforce was shocked at how simply it may obtain a “vital” peak of the printed metallic contacts proper at first of using oblique gravure printing. “Utilizing an applicable 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 an awesome benefit of this printing approach over state-of-the artwork metallization schemes,” he defined.
In subsequent photo voltaic cell simulations, the researchers discovered that with out additional course of optimization, oblique gravure printing could be utilized as rear metallization for SHJ photo voltaic cells with solely a 0.1% loss in conversion effectivity in comparison with display screen printing.
Nevertheless, the researchers famous there may be room for enchancment with this variant of rotary printing. Particularly, they talked about finger resistance and phone resistivity on the contact/indium tin oxide interface may very well be diminished by “adapting ink formulation and annealing circumstances”. As well as, they famous that higher machine alignment may enhance homogeneity of contact fingers, and optimized gravure design may cut back finger width, whereas preserving finger peak at 5 μm or larger.
The workforce asserted that though they experimented with SHJ gadgets, the outcomes could be transferred to different high-efficiency wafer-based cell ideas demanding low-temperature metallization, corresponding to perovskite silicon tandem gadgets.
The analysis workforce included scientists from the Continental Middle for Useful Printing Applied sciences (CFPT), an R&D unit of automotive business provider Continental, and gravure producer Sächsische Walzengravur (SWG).
Its work is described in “Excessive-throughput oblique gravure printing utilized to low-temperature metallization of silicon-based high-efficiency photo voltaic cells,” printed in Vitality Know-how. “The printed outcomes are very encouraging for the entire workforce to maintain on creating this progressive metallization method. Subsequent steps are to cut back the width of the printed contacts and to optimize the design of the metallic grid structure,” Schube mentioned trying forward.
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