Investigations of thick-film-paste rheology for dispensing applications

In order to establish dispensing as a promising metallization process in silicon photovoltaics, equipment and metal pastes require further optimization. By conducting several rheological experiments based on rotational tests, shear thinning as well as thixotropic behavior of thick-film pastes were investigated. Both are crucial parameters for continuous dispensing of 60 m fingers with high aspect ratios. Flow rate fluctuations during dispensing though imply stress peaks that may disturb a continuous paste flow. Thus, a comparison of the flow rate of two pastes was conducted. A comparison of dispensed cells with screen-printed reference cells, on multi-crystalline wafer-material, showed an efficiency increase of 0.3%abs. on average. This is mainly caused by reduced finger widths and higher aspect ratios of dispensed fingers.