The dark side of certain POE encapsulant: Chemical pathways to metallisation corrosion in TOPCon modules

N-type tunnel-oxide passivated contact (TOPCon) cell technology currently accounts for over 60 % of the PV market. Yet, its aluminium-rich front metallisation remains vulnerable to humidity-driven corrosion in glass/back-sheet modules. Building on our previous study, “Buyer Aware: Three new failure modes in TOPCon modules absent from PERC technology”, this work delves deeper into corrosion-induced degradation in TOPCon minimodules encapsulated with ethylene-vinyl acetate copolymer (EVA) and three commercially sourced polyolefin elastomers (POE-A, -B, and -C). After 1000 h of damp-heat exposure (85 °C, 85 % RH), the module with EVA showed a ∼11 % rel drop in P max , mainly attributed to a 50 % rel rise in series resistance (R s ). Spectroscopic analysis suggests that acetic acid released from EVA hydrolysis reacts with solder-flux residues, promoting front metal corrosion at the cell contacts. POE-A and POE-B modules degraded by only 6–10 % rel , neither produced measurable organic acids, and POE-A's antioxidant package appears to inhibit polymer oxidation, confining the residual loss to isolated pre-lamination contaminants. In contrast, POE-C suffered a 55 % rel in P max . Chemical probing reveals a potential cascade of mutually reinforcing reactions that generate a highly acidic micro-environment comprising: (i) carboxylic acids from POE oxidation, (ii) azelaic acid liberated from soldering flux, and (iii) benzoic and phenolic by-products from the ultraviolet (UV) absorber breakdown. This corrosive cocktail potentially accelerates the electrochemical attack on the front cell metallisation, driving a drastic R s increase and catastrophic module failure. The study highlights the pivotal influence of encapsulant formulation, antioxidant, UV absorber chemistry and manufacturing cleanliness on the long-term reliability of TOPCon modules. • EVA modules: ∼11 % rel P max loss due to R s increase caused by acetic acid reacting with soldering flux and corroding contac. • POE-A/B modules: 6-10% rel P max loss due to pre-lamination contaminants reacting with moisture; No acids in POE. • POE-C module: 55% rel P max loss caused by carboxylic acids due to UV absorber breakdown in POE and azelaic acid from flux.