Is TOPCon ready for EVA? Insights from damp heat testing of glass-backsheet modules
Xinyuan Wu, Wu Wei, Yan Zhang, Jiexi Fu, Xutao Wang, J. L. Li, Weiguang Yang, Feng Li, Lin Lv, Yajie Jiang, Bram Hoex
Abstract
Tunnel oxide passivated contact (TOPCon) technology currently dominates the photovoltaic market, and the industry is now focused on enhancing their cost-effectiveness while ensuring their durability in harsher environments. TOPCon modules commonly use a glass–glass bill of materials that incorporates polyolefin elastomer and co-extruded polyethylene encapsulants. Though, for cost and weight reduction, the use of polymer backsheets and lower-cost encapsulants is appealing. This study investigates the performance of glass-backsheet (G-B) TOPCon modules fabricated with two types of silver/aluminum (Ag/Al) pastes: conventional firing with standard Ag/Al paste and low-Al-content Ag paste combined with laser-assisted firing (LAF). The modules, encapsulated with ethylene vinyl acetate (EVA), were subjected to damp-heat testing. Our findings indicate that solar cells with Ag/Al paste exhibit lower stability compared to low Al-content Ag paste; however, acid-rich moisture conditions contribute to glass-frit failures in both types of pastes. Additionally, the rear-side metal contacts, particularly those containing tellurium (Te) compounds, are susceptible to degradation in such environments. Based on these degradation mechanisms, we conclude that further investigation is required to allow for the wider adoption of EVA in TOPCon modules, particularly when a polymer backsheet is used. Ongoing research is essential to optimize these materials and enhance the cost-effectiveness and reliability of TOPCon technology for future applications. • EVA-based GB TOPCon modules with Ag/Al paste lost ∼37% power after 1,000h DH, mainly from FF degradation. • Using low-Al Ag paste with LAF cut power loss to ∼6.2% after 1,000h DH, showing improved thermal stability. • Front-side failure was due to Al oxidation and frit corrosion; rear-side failure involved Te compound breakdown. • Acetic acid from EVA hydrolysis accelerated contact corrosion and delamination at both front and rear interfaces.