KIT Germany study reveals key rheology factors for solar paste printing

Researchers from the Karlsruhe Institute of Technology (KIT), Germany, have published a study on solar cell front-side metallization pastes. The study examined how rheological properties like yield stress, high shear viscosity, slip stress, and slip velocity affected fine-line screen printing. A model system using capillary suspensions with Texanol and four secondary liquids was developed. Yield stress, viscosity, and slip were varied by adjusting particle volume, secondary liquid ratio, and liquid type. Higher yield stress reduced spreading but kept paste laydown similar. High shear viscosity-controlled paste transfer and line width. Excessive slip led to poor line morphology and reduced paste transfer. An optimized paste produced 24 μm lines, a 0.48 aspect ratio, and 23.53 % efficiency with 16 % lower laydown. The study showed that controlling rheology helps reduce silver use in photovoltaics.