Interface Topology and Wetting Dynamics of Laser-Induced Bonds Between Aluminum Foil and Silicon Nitride Passivation in Solar Cells

Metallization in the photovoltaic industry relies heavily on silver, posing significant economic and supply risks for terawatt-scale manufacturing. FoilMet® technology offers an alternative by utilizing aluminum (Al) foil, which is abundant, recyclable, and substantially more cost-effective. This study investigates Laser Metal Bonding (LMB), an ultra-rapid (>10^7 K/s) and ablation-free joining process that enables robust mechanical connections between Al foil and silicon nitride passivation layers while preserving cell efficiency. Presented process parameters reliably maintain the integrity of the passivation layer, ensuring uniform bonds with controlled wetting over a width of 30 μm while achieving processing times of less than 0.6 s. Combining 3D reconstruction and compositional mapping, fundamental adhesion mechanisms are revealed. Numerical process modeling correctly predicts the experimentally observed wetting behavior and ablation thresholds and provides parameter sets for adapting the LMB process to different laser beam geometries, scanning speeds, and laser powers. The thermal threshold (T_wet > 1333 K) governing interfacial interactions is identified, and a comprehensive four-phase process model describing melting, wetting, and solidification is proposed. These insights demonstrate the technical feasibility of silver-free metallization in high-efficiency TOPCon solar cells and pave the way for Al-based interconnection systems that eliminate lead, copper, and silver from photovoltaic modules while significantly reducing metallization costs.