Researchers studied how glass frit chemistry in low-Al silver pastes influences corrosion resistance in LECO-processed TOPCon cells
A lead (Pb)- and boron (B)-rich glass frit showed severe acetic acid-induced degradation, while a barium (Ba)- and zinc (Zn)-modified formulation maintained stable Ag-Si contact integrity
EVA-based glass-backsheet TOPCon modules using the Ba/Zn-modified paste showed only 4%-5% power loss after 1,500 hours of DH85 testing, compared to nearly 30% degradation for the Pb/B-rich paste system
TOPCon is now the dominant crystalline silicon cell architecture, pushing manufacturers to further reduce module production costs. One approach involves replacing polyolefin encapsulants with lower-cost ethylene vinyl acetate (EVA) and adopting glass-backsheet module designs. However, EVA can generate acetic acid under prolonged exposure to heat and humidity, leading to metallization corrosion and module degradation.
Researchers from the University of New South Wales (UNSW) and Chinese solar manufacturer Jolywood studied how glass frit chemistry affects corrosion behavior and long-term reliability in EVA-based TOPCon devices. The team evaluated low-Al silver metallization pastes used in LECO-processed cells and modules.
The researchers evaluated 2 commercial low-Al silver pastes, referred to as Paste A and Paste B. Both achieved similar initial TOPCon cell performance, with efficiencies around 25.2% and fill factors close to 84.5%. However, their glass frit chemistries differed significantly. Paste A used a lead (Pb)- and boron (B)-rich formulation, while Paste B incorporated barium (Ba) and zinc (Zn) modifiers.
To simulate acidic conditions generated by EVA degradation, the team immersed TOPCon cells in a 0.10 mol/L acetic acid solution. Under these conditions, cells metallized with Paste A degraded rapidly, losing 80%-90% of their efficiency within 120 minutes. The degradation was accompanied by a sharp rise in series resistance and severe fill-factor loss caused by metallization corrosion and disruption of the Ag-Si interface.
Cells fabricated using Paste B showed much slower degradation. Voc and Jsc remained largely stable, while increases in series resistance were comparatively moderate. Paste B also maintained stable contact resistance after acid exposure, indicating stronger corrosion resistance.
Microscopic analysis revealed differences between the 2 metallization systems. Cross-sectional SEM images showed severe interfacial delamination and glass frit dissolution in Paste A after acid exposure, leaving gaps between the silver contacts and the silicon surface. Paste B, however, maintained a stable and continuous Ag-Si interface even after aging tests.
The improved stability of Paste B was primarily attributed to Ba’s role in improving the chemical stability of the glass frit. According to the study, Ba forms strong ionic Ba-O bonds that suppress proton-induced leaching in acidic environments. Zn is also believed to support interfacial glass formation and densification.
The team then fabricated glass-backsheet TOPCon modules using a front EPE and rear EVA encapsulation structure and subjected them to 1,500 hours of DH85 testing at 85°C and 85% relative humidity. Modules fabricated with Paste A showed severe degradation, losing 28%-30% of output power, primarily due to fill-factor collapse and increased resistive losses. Electroluminescence imaging revealed extensive darkening around busbar-connected grid regions, indicating contact degradation.
Meanwhile, modules fabricated with Paste B exhibited significantly higher stability. They showed only a relative power loss of 4%-5% after 1,500 hours of DH85 exposure, while Voc and Isc remained nearly unchanged. EL imaging also showed largely uniform brightness and preserved electrical pathways across the module.
The study concludes that the long-term reliability of EVA-based TOPCon modules is governed more by the chemical durability of the glass frit than by the silver phase itself. The findings suggest that Ba/Zn-modified glass frit systems could enable more stable and lower-cost EVA-based glass-backsheet TOPCon modules for industrial deployment.
The study was published in the paper Enabling EVA for TOPCon: How Glass Frit Composition Governs Resistance to Acetic Acid–Induced Corrosion.
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