Improving Wall Slip Behavior of Silver Pastes on Screen Emulsions for Fine Line Screen Printing

Abstract

The ongoing demand for a further reduction of electrode width for solar cell metallization by flatbed and rotary screen printing is one of the main challenges in recent years. The main focus was on the improvement of silver paste printability which is strongly influenced by its rheological behavior. Furthermore, the impact of slip behavior in contact with smooth surfaces e.g. mesh wires and emulsion plays an important role when printing of small electrode width is desired. Therefore, four types of coatings for screen emulsions are investigated in terms of their wall slip behavior with commercial available silver pastes. For this reason, a novel parameter slip efficiency β is introduced which enables the prediction of potential improvements in fine line screen printing by slip effects at the paste-emulsion interface. Furthermore, contact angles on coated surfaces with respective paste solvents are measured and an exponential correlation between both is discovered. Finally, metallization results of a PERC solar cell batch for the two best coating candidates are presented and a correlation between printed electrode width and slip efficiency during screen printing is given. For the best coating, an average finger resistance of 99 Ω/m at an average finger width of 26.2 μm was demonstrated which shows a significant improvement compared to the reference with a finger resistance of 164 Ω/m for 27.7 μm finger width.