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UNSW researchers identify new damp heat-induced failure mechanism in TOPCon solar modules
UNSW researchers identified a new damp-heat degradation mechanism in TOPCon modules with laser-fired contacts, driven primarily by rear-side recombination and open-circuit voltage loss rather than series-resistance increase. The study highlights that magnesium in white EVA encapsulants accelerates degradation, guiding improved encapsulant and backsheet selection for more reliable modules in humid environments.
A research team from the University of New South Wales (UNSW) has identifed a new damp heat-induced degradation pathway in TOPCon modules fabricated with laser-assisted fired contacts.
βUnlike earlier studies dominated by series-resistance increase, the primary degradation driver here is a reduction in open-circuit voltage, linked to enhanced rear-side recombination,β the research's lead author, Bram Hoex, told pv magazine. βThe new degradation mechanism emerged under extended damp-heat (DH) exposure.β
The scientists conducted their analysis on 182 mm Γ 182 mm TOPCon cells fabricated in 2024 with laser-assisted firing.
The TOPCon solar cells employed a boron-doped pβΊ emitter, along with a front-side passivation stack consisting of unintentionally grown silicon dioxide (SiOβ), aluminium oxide (AlβOβ), and hydrogenated silicon nitride (SiNβ:H), capped with a screen-printed H-pattern silver (Ag) contact grid. On the rear side, the structure comprised a SiOβ/phosphorus-doped nβΊ polycrystalline silicon/SiNβ:H stack, also contacted by a screen-printed H-pattern Ag grid.
The researchers encapsulated the cells with different bill of materials (BOMs): two types of ethylene vinyl acetate (EVA); two types of polyolefin elastomer (POE); and one type of EVA-POE-EVA (EPE). They also used commercial coated polyethylene terephthalate (PET) composite (CPC) backsheets.
βThe mini modules were laminated at 153 C for 8 min under standard industrial lamination conditions,β the academics explained. βAll modules underwent DH test at 85 C and 85% relative humidity (RH) in an ASLi climate chamber for up to 2,000 h to study humidity-induced failures.
Image: UNSW, Solar Energy Materials and Solar Cells, CC BY 4.0
The tests showed that maximum power losses ranged from 6% to 16%, with the difference among these values depending strongly on the encapsulation BOM.
βThe modules with POE on both sides were the most stable at around 8%, while those using white EVA on the rear side, especially in combination with EPE, showed the largest losses at around 16%,β said Hoex. βThe primary driver of the degradation was a reduction in open-circuit voltage rather than the increased series resistance after DH testing, which diverges from previous findings that predominantly attributed DH-induced degradation to metallisation corrosion.β
The research team explained that higher levels of degradation were attributable to additives containing magnesium (Mg) in white EVA, which migrate under DH, hydrate, and create an alkaline micro-environment. βThis alkaline chemistry corrodes the rear SiNx passivation layer, increases interfacial hydrogen concentration, induces local pinhole-like defects, and raises dark saturation current, ultimately reducing open-circuit voltage,β Hoex emphasized.
The scientists also explained that, although Mg in white EVA encapsulants and its role in acetic acidβinduced degradation was previously reported, the effect of MgO on performance degradation in TOPCon modules was not explicitly studied.
Their findings are available in the paper βA novel damp heat-induced failure mechanism in PV modules (with case study in TOPCon),βΒ published in Solar Energy Materials and Solar Cells.
βWe hope this work helps refine encapsulant and BOM selection strategies for next-generation TOPCon modules, particularly for humid-climate deployment,β Hoex concluded. βIt provides clear guidance for controlling Mg content in rear encapsulants and optimising rear-side passivation robustness. The mechanistic insights from this study have already informed upstream design changes, substantially reducing risk in commercial modules.β
Other research by UNSW showed the impact of POE encapsulants in TOPCon module corrosion, soldering flux on TOPCon solar cell performance,Β degradation mechanisms of industrial TOPCon solar modules encapsulated with ethylene vinyl acetate (EVA) under accelerated damp-heat conditions, as well as theΒ vulnerability of TOPCon solar cells to contact corrosionΒ andΒ three types of TOPCon solar module failuresΒ that were never detected in PERC panels.
Furthermore, UNSW scientists investigatedΒ sodium-induced degradation of TOPCon solar cells under damp-heat exposure, the role of βhidden contaminantsβ in the degradation of both TOPCon and heterojunction devices, and the impact ofΒ electron irradiationΒ 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.
