Electronic components, such as front contacts of solar cells, are manufactured cost-efficiently using printing and coating technologies, and screen-printing plays a key role in the production of printed electronics. This requires conductive pastes with flow and wetting properties carefully matched to the substrate and the process.
Our focus is to increase the efficiency of solar cells and to reduce the manufacturing costs for the cells through a detailed understanding of the printing process and the development of suitable pastes.
On the one hand, the rheological properties relevant for the screen printing process have to be determined in order to improve conventional silver pastes. On the other hand, an innovative paste concept is developed that significantly improves the electrical properties while simultaneously reducing silver consumption. The pastes are formulated as so-called capillary suspensions, i.e. as three-phase systems containing two immiscible liquids. Stability and printability of the pastes are controlled by capillary bridges between the dispersed silver particles. Such pastes have extremely high storage stabilities and excellent coating properties due to their low agglomerate content. The addition of non-volatile, organic components is not necessary anymore and thus a high conductivity of the sintered layer is guaranteed. The adjustment of flow properties allows for printing of fine lines (< 30 mm) with high aspect ratio, i.e. low shading. High homogeneity along the printed line must also be granted to excel the state of the art in terms of cell efficiency. Further advantages of the new formulation concept are shorter paste production times and simple adjustment of the formulation to changing requirements in the printing process.