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.

Spanish researchers found that semi-transparent silicon PV greenhouses boosted tomato fruit weight by 25% while generating 726.8 kWh over two seasons, outperforming cadmium telluride PV and shaded controls. The PV-Si system balanced sunlight, temperature, and energy, showing strong agrivoltaic potential.

Researchers led by Spain’s Murcian Institute for Agricultural and Environmental Research and Development (IMIDA) have evaluated the impact of different agrivoltaic system designs on tomato crops to determine the level of shading that benefits the plants most.

“The use of four independent, identical greenhouses enables a robust assessment of their respective impacts on microclimate, crop performance, and energy generation,” the team said. “Specifically, the study aimed to evaluate the agronomic and energy performance of two commercially available semi-transparent PV technologies, with distinct light transmission patterns, in comparison with control and shading-net treatments.”

The researchers tested a semi-transparent monocrystalline silicon (PV-Si) greenhouse and a cadmium telluride thin-film (PV-TF) greenhouse against a control greenhouse and one with a shading net.

The study took place in Murcia, Spain, over two tomato-growing seasons: a 120-day winter-spring season from December 2023 to April 2024, and a 98-day spring-summer season from April to July 2024. Murcia’s semi-arid Mediterranean climate features average summer and winter temperatures of 30 C and 12 C, respectively. In both seasons, the team used polyethylene greenhouses measuring 3.9 m long × 2 m wide × 3.1 m high.

Materials under evaluation were installed on the roof and south façade of each greenhouse. The control greenhouse used only the standard polyethylene film, while the shading-control greenhouse added a shading net to selected zones. One solar greenhouse featured monofacial silicon PV modules with 50% transparency, and the other used cadmium telluride (CdTe) modules, also at 50% transparency. Each solar greenhouse had 18 modules—half on the roof, half on the façade—with nominal powers of 59 W for PV-Si and 40 W for PV-TF.

The microclimatic conditions inside each pilot greenhouse were monitored at two-minute intervals. Measurements included air temperature, relative humidity, solar irradiance, and photosynthetically active radiation,” the team explained. “Additionally, soil temperature and humidity were measured at five-minute intervals at depths ranging from 10 to 60 cm in 10 cm increments.”

The testing showed that the PV-Si technology generated an average daily energy output of 3.92 kWh in winter-spring and 4.07 kWh in spring-summer. PV-TF, meanwhile, produced 2.58 kWh and 2.79 kWh, respectively. Total energy generation across both seasons reached 726.8 kWh for PV-Si and 488.4 kWh for PV-TF.

Daily light integral (DLI), representing total photosynthetically active light received by plants each day, averaged 18.1 mol m⁻² in winter-spring and 25.4 mol m⁻² in spring-summer in the Si greenhouse. In the TF greenhouse, DLI averaged 10.8 mol m⁻² and 17 mol m⁻², respectively.

“During the winter-spring cycle, only the control and PV-Si greenhouses maintained DLI values above the minimum threshold required for optimal crop development,” the researchers reported. “Despite a similar number of fruits, the PV-Si greenhouse produced fruits with a mean weight 25% higher than the control, attributed to more favorable nighttime air temperatures and higher soil moisture.”

In winter-spring, the Si greenhouse yielded 21 fruits with an average weight of 74 g, while the TF greenhouse produced 18 fruits averaging 50 g. During spring-summer, the Si greenhouse produced 30 fruits averaging 93 g, compared with 23 fruits at 79 g in the TF greenhouse.

“Overall, the PV-Si system effectively balanced solar radiation management, thermal regulation, and energy production, demonstrating its potential as a suitable technology for agrivoltaic applications,” the team concluded.

The research findings were presented in “Comparative evaluation of semi-transparent monocrystalline silicon and cadmium telluride photovoltaics for tomato cultivation in Mediterranean agrivoltaic greenhouses,” published in Smart Agricultural Technology. Researchers from Spain’s IMIDA, Miguel Hernández University of Elche, and Italy’s University of Bari Aldo Moro have contributed to the study.

A German research team has developed CuInSe₂ micro-concentrator solar cells using laser-assisted metal-organic chemical vapor deposition to grow indium islands directly on molybdenum-coated glass, forming absorber arrays without masks or patterning. The not-yet-optimized micro-modules achieved up to 0.65% efficiency under one sun, with gains of up to 250% under concentrated illumination.

A research team in Germany has developed a copper, indium, selenium (CuInSe₂) micro-concentrator solar device composed of vertically grown absorber islands on a molybdenum (Mo) films.

The scientists used laser-assisted metal-organic chemical vapor deposition (LA-MOCVD) to grow indium (In) islands in a bottom-up approach, instead of depositing a continuous thin film and subsequently patterning it. “The primary novelty of our work is the use of a LA-MOCVD method for the bottom-up growth of indium precursor islands,” corresponding author Jan Berger told pv magazine. “This approach proved to be a fast and reliable technique for simultaneous local growth, importantly offering the possibility to add gallium and copper locally using the same method.”

“The most unexpected finding was that the indium precursor islands formed distinct cluster structures that remained pinned in place, refusing to coalesce into a single large island – even after annealing above the melting temperature of indium,” he added. “Furthermore, it was surprising to see that the structural features of these precursor islands remained clearly visible even after the selenization process.”

Device fabrication begins with glass substrates coated with Mo, which are then processed by LA-MOCVD. In this step, a laser array locally heats the substrate. It decomposes the precursor gas only at defined spots, forming a 7 × 7 array of indium islands without the need for masks or patterning. A thin copper layer is subsequently deposited, and the stack is selenized to form CuInSe₂ absorber islands.

Afterward, the samples are etched to remove unwanted material, coated with photoresist for electrical isolation, and patterned with a laser to form openings. The solar cell is then completed by depositing a cadmium sulfide (CdS) buffer layer, followed by intrinsic zinc oxide (i-ZnO) and aluminum-doped zinc oxide (AZO) window layers. Finally, each array of 49 micro-cells is contacted and measured as a single module, with a device structure of glass/Mo/CIS absorber/ cadmium sulfide (CdS)/i-ZnO/AZO.

Overall, the team produced nine micro-modules and tested four of them. Initial measurements were conducted under one sun, followed by increasing intensities up to 17 suns to simulate concentrator conditions. These not-yet-optimized arrays achieved a conversion efficiency of up to 0.65% under one sun, with efficiency rising under higher illumination—gains of around 60% at lower concentrations and up to 250% at 17 suns.

“Functional devices were successfully produced, but notable key challenges were identified, particularly related to the intensity distribution of diffractive optical element (DOE), the initial morphology of indium islands, and process repeatability. Addressing these challenges in terms of material quality and process control is essential,” the team explained. “Once resolved, the LA-MOCVD method holds significant promise as a rapid and resource-efficient production technique for next-generation micro-concentrator photovoltaics.”

The new cell concept was presented in “CuInSe2-based micro-concentrator solar cells fabricated from In islands grown by laser-assisted MO-CVD,” published in Solar Energy Materials and Solar Cells. Scientists from Germany's University of Duisburg-Essen, the Leibniz Institute for Crystal Growth, the Federal Institute for Materials Research and Testing, Brandenburg University of Technology Cottbus-Senftenberg, and the engineering company Bestec have participated in the study.

Researchers in Iraq have developed biomimetic leaf vein–inspired fins for photovoltaic panels, with reticulate (RET) venation reducing panel temperature by 33.6 C and boosting efficiency by 18% using passive cooling. Their study combines 3D CFD simulations and electrical evaluations to optimize fin geometry, offering a sustainable alternative to conventional cooling methods.

A research group from Iraq’s Al-Furat Al-Awsat Technical University has numerically investigated the thermal and electrical performance of PV panels integrated with leaf vein–inspired fins. They have simulated four types of venation used by plants, namely pinnate venation (PIN), reticulate venation (RET), parallel venation along the vertical axis (PAR-I), and parallel venation along the horizontal axis (PAR-II).

“The key novelty of our research lies in introducing and systematically optimizing biomimetic leaf vein–inspired fin geometries as passive heat sinks for photovoltaic panels,” corresponding author Yasser A. Jebbar told pv magazine. “While conventional cooling approaches rely on simple straight fins, fluids, or active systems, our study is among the first to directly translate natural leaf venation patterns—particularly RET structures—into manufacturable backside fins specifically tailored for PV thermal and electrical performance.”

The team combined detailed 3D computational fluid dynamics (CFD) modeling with electrical efficiency analysis to identify geometries that maximize heat dissipation without additional energy input or water consumption. Next steps include experimental validation of the leaf vein fin designs under real outdoor conditions, particularly in hot climates.

The simulated PV panel consisted of five layers: glass, two ethylene-vinyl acetate (EVA) layers, a solar cell layer, and a Tedlar layer, with a copper heat sink and fins attached. All fin configurations were initially 0.002 m thick, 0.03 m high, and spaced 0.05 m apart. Panels measured 0.5 m × 0.5 m, with a surrounding air velocity of 1.5 m/s and incident irradiance of 1,000 W/m².

RET fins outperformed all other designs, reducing operating temperature by 33.6 C and increasing electrical efficiency from 12.0% to 14.19% —an 18 % relative improvement—compared to uncooled panels.

“This temperature reduction rivals, and in some cases exceeds, water-based or hybrid cooling methods, despite relying solely on passive air cooling,” Jebbar noted. The study also highlighted the significant impact of fin height, more than spacing or thickness, on cooling performance.

The team further optimized the RET fins, varying spacing from 0.02–0.07 m, height from 0.02–0.07 m, and thickness from 0.002–0.007 m. The optimal geometry—0.03 m spacing, 0.05 m height, and 0.006 m thickness—achieved the maximum 33.6 C temperature reduction and 18% efficiency gain.

The novel cooling technique was described in “Improving Thermal and Electrical Performance of PV Panels Using Leaf Vein Fins,” published in Solar Energy. Researchers from Iraq’s Al-Furat Al-Awsat Technical University, University of Kerbala, and Sweden’s University of Gävle have participated in the study.

Scientists have grown organic romaine lettuce under 13 different types of PV modules, in an unusual hot Canadian summer. Their analysis showed lettuce yields increased by over 400% compared to unshaded control plants.

A research group from Canada’s Western University has investigated the performance of organic romaine lettuce, a heat-sensitive crop, under a broad range of agrivoltaic conditions. The test was conducted in London, Ontario, in the summer of 2025, during which 18 days had temperatures over 30 C.

“Our study explores how agrivoltaic systems can be tailored to optimize crop growth, especially under extreme heat conditions, while contributing to sustainable energy generation,” corresponding researcher Uzair Jamil told pv magazine.

“This becomes especially relevant in the context of climate change, where we are experiencing temperature extremes across the world,” Jamil added. “We examined the performance of organic romaine lettuce under thirteen different agrivoltaic configurations – ranging from crystalline silicon PV to thin-film-colored modules (red, blue, green) – in outdoor, high-temperature stress conditions.”

More specifically, the experiment included c-Si modules with 8%, 44% and 69% transparency rate; blue c-Si modules with transparency of 60%, 70%, and 80%; green c-Si modules with transparency of 60%, 70%, and 80%; and red c-Si modules with transparency of of 40%, 50%, 70%, and 80%.

All agrivoltaics installations had a leading-edge height of 2.0 m and a trailing-edge height of 2.8 m, and the modules were oriented southwards at 34◦. Pots with organic romaine lettuce were placed under all configurations, along with three pots fully exposed to ambient sunlight without shading, used as controls.

In addition to measurements against the control, the scientific group has compared the results to the national average per-pot yield for 2022, which included less high-temperature days and was therefore considered typical. Those data points were taken from agricultural census data, which later enabled the researcher also to create nationwide projections of their results.

“Lettuce yields increased by over 400% compared to unshaded control plants, and 200% relative to national average yields,” Jamil said about the results. “60% transparent blue Cd-Te and 44% transparent crystalline silicon PV modules delivered the highest productivity gains, demonstrating the importance of both shading intensity and spectral quality in boosting plant growth.”

Jamil further added that if agrivoltaic were to scale up to protect Canada’s entire lettuce crop, they could add 392,000 tonnes of lettuce.

“That translates into CAD $62.9 billion (USD $46.6 billion) in revenue over 25 years,” he said. “If scaled across Canada, agrivoltaics could also reduce 6.4 million tonnes of CO2 emissions over 25 years, making it a key player in reducing the agricultural sector’s environmental footprint.”

The results of the research work were presented in “Enhancing heat stress tolerance in organic romaine lettuce using crystalline silicon and red, blue & green-colored thin film agrivoltaic systems,” published in Solar Energy.

Cubenergy has launched FlexCombo 2.0, a scalable battery energy storage system for utility, commercial, and industrial applications, offering up to 16 MWh capacity with LFP batteries. Its modular design, advanced BMS, and cloud-based operations enable easy installation, seamless expansion, and efficient grid integration, according to the manufacturer.

Cubenergy, a Chinese manufacturer of battery energy storage systems (BESS), has introduced a new energy block designed for utility, commercial, and industrial (C&I) applications.

The product, named FlexCombo 2.0, uses the company’s 835 kWh FlexCombo D2 batteries. It is available in three configurations: 10, 12, or 12 batteries, providing a total capacity of 8 MWh, 10 MWh, or 16 MWh, respectively.

“With the FlexCombo D2 modular design and parallel architecture, FlexCombo’s core advantage lies in its long-term scalability,” the company said in a statement. “It enables seamless capacity growth and effortless integration with power generation systems (PGS), simplifying deployment and accelerating delivery for ultimate flexibility.”

The FlexCombo D2 batteries feature lithium iron phosphate (LFP) chemistry, offering a lifespan of 8,000 cycles at 70% capacity retention, according to the manufacturer.

Each battery measures 2 m x 1.68 m x 2.55 m and has a weight of up to eight tons. They carry an IP55 protection rating. Each block also comes with a power conversion system (PCS) rated at 430 kW AC with an IP66 protection grade. Optional medium-voltage (MV) transformers are available, with AC power ratings of either 8,800 kVA or 5,250 kVA.

“The FlexCombo 2.0 is designed primarily for utility and C&I applications, including renewable energy arbitrage, stand-alone grid stabilization, factories, and commercial buildings,” the company stated. “This integrated, easy-to-install BESS can be quickly connected and aligned with project requirements, while the advanced Active Balancing battery management system (BMS) and cloud-based operations provide a superior user experience.”

The South Korean giant said its new EHS All-in-One provides air heating and cooling, floor heating, and hot water from a single outdoor unit. It can supply hot water up to 65 C in below-zero weather.

South Korean tech giant Samsung has launched a new all-in-one heat pump for residential and commercial use.

Dubbed EHS All-in-One, the system provides air heating and cooling, floor heating, and hot water from a single outdoor unit. It is initially released for the European market, with a Korean rollout expected within a year.

“It delivers stable performance across diverse weather conditions. It can supply hot water up to 65 C even in below-zero weather and is designed to operate heating even in severe cold down to -25 C,” the company said in a statement. “The system also uses the R32 refrigerant, which has a substantially lower impact on global warming compared with the older R410A refrigerant.”

The product is an upgrade to the EHS Mono R290 monobloc heat pump that the company released in 2023. The company has enlarged the propeller fan and used a high-capacity motor in the novel model, reducing the number of fans from two to one. That results in a design with a height of about 850 mm, approximately 40% lower than before.

“The system also introduces a new Heat Recovery feature, which does not release waste heat from the cooling process to the outside but recycles it. Using this feature can boost the energy efficiency of water heating by more than twice under certain conditions,” Samsung added. “It also includes an ‘AI Saving Mode’ that can reduce energy consumption by up to 17%.”

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.”