Rheological effect on screen-printed morphology of thick film silver paste metallization

Abstract

Up to now the topography of thick film silver paste metallization is still a great challenge to the crystalline silicon solar cell manufacturers due to lack of overall understanding about the dependence of screen-printed morphology on paste rheology. In this article, we demonstrate that both the shear thixotropy and wall slip are primary rheological behaviors of pastes affecting screen-printed morphology. By comparison among three different commercial pastes, the association of screen-printed morphology with apparent viscosity and slip velocity of pastes were investigated. The results from printing finger lines with designed width of 45 μm show clearly that the widening degree of lines is associated with the paste viscosity, and the height and cross-sectional profile of lines mainly rely on the wall slip velocity of paste passing through screen meshes. Briefly, the lower the apparent viscosity, the wider the lines; and the greater the wall slip velocity, the less the line height and more likely the formation of trapezoidal cross-sectional profile with larger area. Our study shows for the first time that the wall slip of pastes may produce significant influence on cell efficiency, since its influence on screen-printed morphology is considerably remarkable and vital.