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

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 mu m 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.