Correlations between finger geometry and dispensing paste rheology

An optimum adjustment of printing medium and machine parameters is essential to establish dispensing as an alternative front side metallization process for silicon solar cells. In previous studies [1-3], paste rheology was found to have a major impact on resulting finger geometry and process stability. In order to find a good balance between printability and resulting contact geometry, different dispensing pastes were evaluated and dispensed on Cz-Si 156x156 mm² precursor material equipped with standard aluminium printed back surfaces and pre-printed front side busbars. In order to determine the optimum co-firing temperature, three completely screenprinted cell groups were processed in parallel serving as reference cells. Cell results were investigated concerning finger geometry and electrical parameters. With increasing paste elasticity, the finger width could be reduced down to 43 ?m. Furthermore, contact width indicating possible paste spreading on the wafer surface as well as finger necking turned out to be a crucial geometrical parameter of dispensed contact fingers. Once more, the enormous potential of dispensing as a front side metallization technique could be demonstrated.