Researchers from University of New South Wales and Jolywood found that corrosion-induced degradation in TOPCon solar cells is primarily governed by glass frit chemistry in low-aluminum silver metallization. Their findings show that barium-zinc-modified frits significantly improve resistance to acetic-acid and damp-heat stress, enabling more stable silver-silicon interfaces and reduced module-level power loss.
A research team from the University of New South Wales (UNSW) and Chinese solar module manufacturer Jolywood have investigated the causes of corrosion-induced degradation in TOPCon solar cells fabricated with low aluminum (Al) silver (Ag) paste and ethylene–vinyl acetate (EVA) and EVA/polyolefin/EVA (EPE) encapsulant and have found that the glass frit chemistry plays a key role in the degradation process.
“Our work establishes a direct correlation between cell-level acetic-acid corrosion and module-level damp-heat degradation in laser-assisted firing (LAF)-processed TOPCon devices,” corresponding author Bram Hoex told pv magazine. “We demonstrated that glass-frit chemistry is a critical parameter governing metallization reliability in EVA-based TOPCon modules.”
“The research also provides practical guidance for designing corrosion-resistant low-Al Ag pastes compatible with cost-effective glass–backsheet module architectures and supports the broader industrial transition toward reliable EVA-enabled TOPCon technologies,” he went on to say. “We believe this work provides important insight into how metallization design and encapsulant chemistry interact under damp-heat (DH) stress, particularly as the industry pushes toward lower-cost bill of material (BOMs) for TOPCon modules.”
The researchers conducted a series of tests both at the cell and module levels.
As for the cells, they were manufactured on G10 n-type Czochralski (Cz) silicon wafers with two types of low-aluminum silver pastes. Both cell types underwent firing and LAF processes, differing only in front-contact metallization referred to as Pastes A and B. Paste compositions were analyzed using inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma optical emission spectroscopy (ICP-OES) to quantify silver and trace elements.
To simulate the acidic conditions caused by EVA degradation, cleaned cells were immersed in 0.10 mol/L acetic acid at room temperature. Electrical performance was monitored before and after exposure through I–V measurements, photoluminescence (PL) imaging, series resistance mapping, and contact resistivity testing. Additional microstructural and chemical analyses were performed using scanning electron microscopy (SEM), focused ion beam (FIB) milling, energy-dispersive spectroscopy (EDS) mapping, and elemental quantification to examine corrosion effects at the Ag–Si interface.
At the module level, glass/EPE/TOPCon/EVA/backsheet structures were subjected to damp-heat testing at 85 C and 85% relative humidity in accordance with IEC 61215 standards. Periodic electroluminescence (EL) imaging and electrical measurements tracked degradation during accelerated aging. After 1,500 hours of damp-heat exposure, the modules were re-evaluated to quantify performance losses and identify degradation patterns.
Image: UNSW, Progress in Photovoltaics, CC BY 4.0
The cell-level acetic acid testing showed strong performance differences between TOPCon solar cells using Pastes A and B, despite similar initial efficiencies of around 25.2%. Paste A degraded rapidly, losing between 80% and 90% efficiency within 120 minutes due to a sharp rise in series resistance and severe fill factor loss caused by corrosion at the Ag–Si interface. In contrast, Paste B showed much slower degradation, with stable open-circuit voltage and shor-circuit current over 240 minutes and only moderate increases in series resistance.
“Under accelerated acetic-acid exposure, Paste A showed rapid degradation, including catastrophic increases in series resistance and severe loss of electrical performance,” stressed Hoex. “In contrast, Paste B maintained stable contact resistivity, preserved Ag–Si interfacial integrity, and exhibited significantly slower degradation.”
Contact resistivity measurements confirmed severe, nonuniform degradation in Paste A, while Paste B maintained stable, low-resistance contacts. Structural analysis alos evealed that Paste A contains a lead-phosphorous (Pb/B)-rich glass frit without barium (Ba), which is highly vulnerable to acid-induced dissolution. Paste B incorporates Ba- and zinc (Zn)-modified glass chemistry, which improves resistance to acidic corrosion. “ Ba-containing glass frits exhibited substantially improved chemical durability, suppressing ionic leaching and preserving interfacial continuity under acidic and humid conditions,” Hoex explained.
SEM and FIB imaging, meanwhile, showed that Paste A suffered near-complete dissolution of the interfacial glass layer, leading to voids and contact failure, whereas Paste B preserved a continuous Ag–Si interface. Moreover, module-level damp-heat testing confirmed the same trend, with Paste A modules losing between 28% and 30% power due to fill factor-driven losses, while Paste B modules degraded by only by 4% and 5%. EL imaging further highlighted severe, nonuniform resistive damage in Paste A modules compared to stable performance in Paste B.
“Overall, these results demonstrate that the chemical durability of the glass frit rather than the metallic Ag phase governs metallization reliability in LAF TOPCon devices,” the scientists concluded. “Incorporating alkaline earth modifiers such as Ba and Zn into the glass network provides an effective means to mitigate acetic acid- and moisture-induced degradation, thereby enabling stable Ag–Si interfaces and extended module lifetimes.”
Their findings were presented in “Enabling EVA for TOPCon: How Glass Frit Composition Governs Resistance to Acetic Acid–Induced Corrosion,” published in Progress in Photovoltaics.
Other research by UNSW showed the impact of POE encapsulants in TOPCon module corrosion, soldering flux on TOPCon solar cell performance, degradation mechanisms of industrial TOPCon solar modules encapsulated with ethylene vinyl acetate (EVA) under accelerated damp-heat conditions, as well as the vulnerability of TOPCon solar cells to contact corrosion and three types of TOPCon solar module failures that were never detected in PERC panels.
Furthermore, UNSW scientists investigated sodium-induced degradation of TOPCon solar cells under damp-heat exposure, the role of ‘hidden contaminants’ in the degradation of both TOPCon and heterojunction devices, and the impact of electron irradiation on PERC, TOPCon solar cell performance.
More recently, another UNSW rsearch team developed an experimentally validated model linking UV-induced degradation in TOPCon solar cells to hydrogen transport, charge trapping, and permanent structural changes in the passivation stack. Furthermore, UNSW and Jolywood also investigated how effectively the laser-assisted firing process developed by Jolywood itself, the so-called Jolywood Special Injected Metallization (JSIM), enhances the efficiency of industrial-scale TOPCon solar cells by reducing Si-metal contact recombination and have found the manufacturing step can increase cell efficiency by approximately 0.6% absolute compared to the baseline single-step firing process.
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