Researchers on the University of New South Wales declare to have recognized new TOPCon contact degradation mechanisms which might be strongly influenced by the mix of ions and aluminum-silver paste compositions. The most important mechanism of decay is a major improve in sequence resistance.
Scientists from Australia’s University of New South Wales (UNSW) and Chinese-Canadian PV module producer Canadian Solar investigated the degradation of business TOPCon photo voltaic cells subjected to accelerated check situations of 85 C and 85% relative humidity below the so-called dump warmth check. (DH85).
“Our findings spotlight the vulnerability of TOPCon photo voltaic cells to contact corrosion, highlighting the electrochemical reactivity of metallization as a possible threat for long-term module operation,” the lead writer of the analysis, Bram Hoex , stated. pv journal. “This examine gives essential insights into TOPCon cell degradation mechanisms, important for optimizing the efficiency and bettering the long-term reliability of those modules.”
Hoex defined that the examine was complementary to the earlier work of the analysis group and expanded it by utilizing two forms of sodium-containing salts that allowed the researchers to watch the variations within the chemical reactions happening. “This improved understanding of the underlying chemistry that explains degradation is vital to additional bettering TOPCon’s stability,” he added.
The group printed a primary paper in late April, the place it recognized three new forms of TOPCon photo voltaic module failures which have by no means been seen in PERC panels. This work is meant to analyze the influence of payments of supplies (BOM) on the reliability of each commercially out there PERC and TOPCon photo voltaic cells.
“The outcomes actually stunned us,” Hoex stated pv journal at the moment. “We count on polyolefin elastomers (POE) to usually carry out effectively, however we acknowledge that some POEs carry out poorly. This might be as a result of varied components utilized in POE reacting with the soldering flux and the metallization leading to contact breakdown.
In new analysis, scientists have discovered important variations between the sensitivity of the back and front of the TOPCon photo voltaic cells when the degradation is brought on by two sodium-containing salts – sodium bicarbonate (NaHCO).3) and sodium chloride (NaCl).
Academics carried out exams with 158.75 mm x 158.75 mm G1 n-type TOPCon photo voltaic cells with 5 busbars. Their common energy conversion effectivity is 23.1%.
On the entrance aspect, the gadgets are made with a boron-diffused emitter lined with aluminum oxide (Al2or3) and silicon nitride (SiNx), in addition to a silicon oxynitride (SiOyNz) stack that gives floor passivation and acts as an antireflection coating (ARC). On the again aspect, the cells have a TOPCon structure primarily based on a tunneling silicon oxide (SiO2) layer paired with a phosphorus-doped poly-Si layer, in addition to a SiNx ARC layer.
“The front-side metallization consists of a mix of silver (Ag) and aluminum (Al, 3-5 at.%) as conducting materials, whereas the rear-side steel contact consists solely of Ag for conduction,” the researchers defined.
Image: UNSW, Solar Energy Materials and Solar Cells, Common License CC BY 4.0
The DH85 check was carried out utilizing scanning electron microscopy (SEM) photos of 5 cell samples: reference cell handled solely with deionized water (DIW); cells uncovered to NaHCO3 on the entrance aspect; NaHCO3 on the again aspect; cells uncovered to NaCl on the entrance aspect; and cells uncovered to NaCl on the posterior aspect.
Regarding the primary group, scientists discovered that exposing TOPCon cells to excessive humidity at excessive temperatures for lengthy intervals of time doesn’t naturally result in deterioration. For different teams, nevertheless, the effectivity degradation is important.
“Our accelerated check utilizing NaCl precipitated extreme degradation of energy conversion effectivity leading to a 92% relative discount, whereas NaHCO3 resulted in a 5% relative discount in effectivity,” stated Hoex. “The most important deterioration mechanism is a major improve in sequence resistance (Rs), most likely attributable to electrochemical reactions throughout the silver-aluminum (Ag/Al) paste.
“When utilized to the again of the TOPCon photo voltaic cell, NaHCO3 will increase recombination and damages the contacts, resulting in a 16% discount in effectivity after 100 hours of DH85 testing,” added Hoex. “On the opposite, NaCl primarily will increase recombination and doesn’t appear to have an effect on the contact, inflicting a 4% lack of effectivity. Further investigation revealed the mechanisms of decay of the steel contacts on the again, particularly oxidation on the Ag-Si interface.
The scientists emphasised that Ag/Al pastes are uncovered to long-term stability dangers when uncovered to contaminating ion ranges and stated that different combos of ion ranges ought to be investigated.
“In abstract, this examine reveals that TOPCon contact degradation mechanisms are considerably influenced by the mix of ions and paste compositions,” the researchers stated. “This presents essential insights into the degradation patterns and underlying components affecting the steel contacts of TOPCon photo voltaic cells, which can assist to judge reliability on the module stage.”
Their findings are on paper”Revealing the origin of steel contact failures in TOPCon photo voltaic cells by accelerated damp-heat testing,” printed in Solar Energy Materials and Solar Cells. The analysis crew additionally consists of lecturers from Nantong University and Shanghai Jiao Tong University in China.
In one other examine printed in early April, the identical analysis crew labored with scientists from Chinese panel maker Jolywood to design a laser-assisted firing course of in TOPCon photo voltaic cell manufacturing that reportedly improves contact in high quality and corrosion resistance, whereas additionally lowering manufacturing prices.
Called Jolywood Special Injected Metallization (JSIM), the brand new approach consists of a laser-assisted firing course of that makes use of a custom-made silver (Ag) paste for the entrance contact formation of TOPCon photo voltaic cells. This is a low temperature firing technique supposed to facilitate penetration of the paste by way of the anti-reflection coating on the entrance of the cell.
“The JSIM know-how is already in high-volume manufacturing at Jolywood and different firms are growing and implementing their very own variations of laser-assisted firing,” the lead writer of the analysis, Bram Hoex, talking pv journal at the moment. “Jolywood is among the first producers to scale up TOPCon know-how to excessive quantity manufacturing.”
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