A UNSW-led team found that annealing conditions significantly affect stress, strain, and microstructure in copper-plated heterojunction solar cell contacts, with fast annealing increasing microstrain in both copper and indium tin oxide.

A team of scientists led by Australia's University of New South Wales (UNSW) has studied how stress and strain evolve in copper (Cu)-plated contacts on heterojunction (HJT) solar cells under various annealing conditions. Their work specifically examined how annealing affects the material properties of Cu, indium tin oxide (ITO), and silicon (Si).

“We applied multiple characterization methods to understand how annealing conditions influence stress and strain in Cu-plated HJT cells,” co-author Pei-Chieh Hsiao told pv magazine. “Our results show that Cu contacts on HJT cells need careful assessment to balance adhesion with mechanical integrity.”

Hsiao highlighted the importance of controlling the microscopic structure of copper contacts to limit mechanical stress in HJT solar cells. “Ideally, plated Cu with a low defect density and (100) crystal texture is preferred,” he explained. “This reduces stress in Si after annealing because of a lower Young’s modulus. The preferred texture can be achieved by adjusting the electrolyte or plating parameters, and annealing can then be optimized to minimize thermal strain while preserving the (100) orientation.”

The team began with silicon heterojunction G12 half-cut n-type precursors measuring 210 mm × 105 mm. The cells were coated with a resin-based mask to restrict copper plating, with selective openings created via a collimated light source. Copper was then plated onto the exposed ITO surface using an acid-based electroplating solution at a current density of 42 mA/cm².

The team compared three annealing methods. In self-annealing, samples were stored at room temperature in a low-humidity environment. Fast annealing (same day) was carried out in compressed dry air at 205 ± 5 C for 45 seconds under approximately 15 suns of illumination. Fast annealing (next day) used the same conditions but was performed roughly 24 hours after plating.

“Due to the limitation of low temperature processing of HJT cells, fast annealing was performed at 200 C, which is lower than the grain growth stage at over 250 C,” Hsiao said. “It means that annealing of plated Cu contacts on HJT cells would perform distinctly from that on PERC or TOPCon cells, where higher annealing temperatures are permitted and improved contact adhesion has been demonstrated.”

The team then examined the samples in a series of tests. First, nanoindentation was used to measure the mechanical strength and stiffness of the plated copper. Second, X-ray diffraction (XRD) was used to examine the crystal structure of the copper and the underlying ITO layer. Finally, Raman spectroscopy was used to map the mechanical stress induced by the copper contacts in the silicon, especially near the contact edges.

The analysis showed that no significant differences were found in yield strength or plastic response of plated Cu, which was consistent with the comparable Cu grain size. Moreover, XRD patterns showed fast annealing reduced the Cu lattice parameter and promoted grain growth in the Cu (200) crystallographic orientation, while simultaneously increasing the ITO lattice parameter and full width at half maximum (FWHM).

As a result, microstrains in both Cu and ITO rose under rapid annealing, with the scientists noting that Raman spectroscopy revealed approximately 2 μm-wide regions of high local stress in the silicon along the plated Cu fingers, with stress being lower in self-annealed Cu and higher in fast-annealed Cu.

These results indicate that minimizing defects and promoting a preferential (100) texture in plated Cu can reduce stress transfer to Si and ITO. Maintaining uniform plating conditions and careful surface preparation are also essential for achieving optimal texture and adhesion. Overall, self-annealing is preferred when comparable contact adhesion can be achieved, as it preserves the (100) orientation and minimizes thermal strain.

The research work was described in “Stress and strain analysis of Cu plated contacts on HJT cells under different annealing conditions,” published in Solar Energy Materials and Solar Cells. Scientists from Australia's University of New South Wales and technology company SunDrive Solar have contributed to the research.

In early January, a research team from UNSW and Chinese-Canadian solar module maker Canadian Solar investigated how HJT solar cells are hit by sodium (Na) and moisture degradation under accelerated damp-heat testing and has found that most degradation modes predominantly affect the cells themselves, making cell-level testing the preferred approach.

A month later, another UNSW team assessed the impact of soldering flux on HJT solar cells and found that the composition of this component is key to prevent major cracks and significant peeling.

After hitting an all-time high of $121.65/oz on Jan. 29, silver prices have tumbled to $79.44/oz, with analysts warning of a potential drop toward $50/oz.

After reaching an all-time high of $$121.65 per ounce (oz) on Jan. 29, silver prices have fallen sharply in recent days, dropping to $79.44/oz this morning.

The downturn had been anticipated by two analysts interviewed by pv magazine on Jan. 27, who warned that the steep rally seen in previous weeks could reverse abruptly in the days ahead.

One of the two analysts, Mike McGlone, senior commodity strategist at Bloomberg Intelligence, said the price could stabilize around $50/oz, although he did not provide a timeframe for when this new trend might materialize.

“Reversion toward $50 appears as a normal path for the commodity known as the ‘devil's metal' due to its volatility,” he told pv magazine.

Rhona O’Connell, head of market analysis for EMEA and Asia at StoneX, said on Jan. 27 that investors might soon rethink their rush into silver. She explained that speculative buying had pushed the metal into risky territory, making prices vulnerable to a sharp correction. O’Connell also said fears of potential U.S. tariffs fueled the recent rally, swelling COMEX inventories as metal flowed into the U.S. Further gains are unlikely, she added, dismissing even $100/oz as unsustainable and warning of a potentially severe price reversal.

Silver prices surged by approximately 130% in the past six months and around 243% over the past year. The average silver price was $28.27/oz in 2024, $23.38/oz in 2023, and $21.80/oz in 2022.

Wuxi DK Electronic Materials is pursuing two patent infringement cases against domestic competitors, seeking injunctions, equipment destruction, and combined damages of CNY 400 million ($57.5 million).

Wuxi DK Electronic Materials has filed two patent infringement lawsuits with the Jiangsu High People’s Court against Jiangsu Riyu Photovoltaic New Materials and Suzhou Jinyin New Materials Technology , seeking CNY 200 million in damages and related legal costs in each case.

The company said both filings have been formally accepted and registered by the court, although hearing dates have not yet been scheduled.

The lawsuits concern two Chinese invention patents, ZL201180032359.1 and ZL201180032701.8, covering thick-film conductive paste formulations for semiconductor devices, including solar cells. DKEM said the patents are held by its subsidiary Solamet Electronic Materials and relate to lead-tellurium-lithium and oxide-based paste technologies.

DKEM is seeking injunctions to halt the manufacture, sale, and offering for sale of the allegedly infringing pastes. The company is also requesting the destruction of dedicated production equipment and molds, and compensation for economic losses, enforcement costs, and related expenses.

The patents trace back to the intellectual property portfolio of DuPont’s former Solamet photovoltaic paste business, acquired by another entity in 2021 for $190 million. DKEM later consolidated control of the Solamet assets and associated intellectual property.

Suzhou Jinyin is described in Chinese financial reporting as a leading supplier of front-side silver paste for solar cells, ranking third globally by market share. Founded in 2011, it was later acquired by listed electronics firm Suzhou Good-Ark Electronics. Jiangsu Riyu is a fast-growing paste supplier that filed a Hong Kong listing application in 2025, with plans to expand into n-type and back-contact paste products.

This follows earlier high-value patent actions by DKEM. In 2025, its subsidiary filed a suit against Zhejiang Guangda Electronic Technology seeking similar remedies. A Solamet-linked entity also pursued related claims against Changzhou Juhe New Materials in 2021, with domestic and overseas disputes reportedly settled in August 2022.

Separately, DKEM flagged earnings pressure, forecasting a net loss of CNY 200 million to CNY 300 million for 2025, primarily linked to non-operating factors, according to Chinese financial media.

With silver prices rising, more large solar manufacturers are expected to switch to copper for cell metallization. Radovan Kopecek of ISC Konstanz tells pv magazine that he expects the entire industry to follow. Ning Song of the University of New South Wales says a small efficiency tradeoff may be acceptable if the cost savings are significant and do not introduce new reliability risks.

The recent surge in silver prices has eased slightly, with prices per troy ounce now just below the all-time high of over $94 per troy ounce reached earlier this week. Following announcements by Chinese module manufacturer Longi announced that it is moving toward copper-based metallization, and by China-based metallization paste supplier DK Electronic Materials that a gigawatt-scale customer will adopt its high-copper paste for commercial production, 2026 could mark a key milestone in the PV industry’s phase-down of the costly metal.

“I do think that the industry will follow in those footsteps, as the PV industry is a ‘follower industry.” When the big players start with something, the others follow,” Radovan Kopecek, the co-founder and director of German research institute the International Solar Energy Research Center Konstanz (ISC Konstanz), told pv magazine. “An immediate transition to copper is technically and economically feasible. Copper screen printing can be implemented quickly, and we have received many inquiries about it.”

According to Kopecek, project developers are “absolutely” ready to embrace copper-metallized products, adding that when the technology is properly implemented, performance does not differ from that of silver-metallized modules. “However, I do not expect the industry to abandon silver completely,” he said. “Silver will remain at around 2 mg to 3 mg per watt, as it is still needed for firing through, as a diffusion barrier, and to establish contact with the emitter.”

Ning Song, from the University of New South Wales (UNSW) in Australia, explained that even if adopting a high-copper paste results in a small efficiency drop, the price trade-off should be acceptable to manufacturers. “That trade-off is acceptable if it does not introduce new reliability risks. Ultimately, the decision depends on how well the efficiency loss can be offset at the module and system level,” she told pv magazine.

Song's team is currently working to identify practical pathways to reduce silver usage in PV cells, both through incremental improvements to existing screen-printed metallization and longer-term exploration of alternative paste systems. “In the short term, aggressive silver thrifting within existing screen-printing processes is the most commercially ready option, as it minimizes disruption to current manufacturing lines,” she stated.

“From a purely technical perspective, the most promising long-term solution is the one that delivers the best combination of low contact resistance, minimal recombination losses at the contacts, high conductivity, sufficient ductility to enable narrow, well-shaped gridlines with reduced optical shading, and robust long-term reliability,” she said. “That is regardless of the specific metal used.”