A large number of solar cells is metallized by printing and firing glass containing silver pastes. However, the contact formation is not fully understood so far. There is still a lack of understanding the role of the glass phase in the complex contact formation scenario because single effects could not been seperatly observed and evaluated up to now. To overcome this, an in-situ method to observe the contact formation via a contact resistance measurement was introduced. A special measuring device was applied to characterize two typical front side pastes, featuring a PbO-containing as well as a PbO-free glass frit during firing. The viscosity of the paste glass showed decisive influence for the etching of the anti-reflection coating (ARC). The ARC was opened immediately after entering the softening range of the respective glass, regardless of large differences in glass chemistry. Furthermore, the viscosity-temperature behaviour of the paste glass determines the intensity of the redox-reaction and related silver precipitation at the interface, which takes part between ARC opening and glass resolidification. The cooling slope was confirmed to have decisive influence on the final interface conductivity, because a crucial part of silver colloids can be formed here

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AbstractÀAerosol jet printing is a rather new technology for the deposition of thick film structures offering high line and space resolution. This method offers high potential for miniaturization for thick film structures. The advantages of this technology could be shown with inks carrying a single solid powder (e.g., silver, platinum, ceramic, or glass powder). One of the challenges in printing solid powder mixtures is the differences in the aerodynamic properties of different powders. Those differences result in changes of the mixing ratio within the aerosol jet and therefore poor reproducibility in the finished film.In this work, thick film resistors consisting of RuO 2 with particle size <1 mm as the conducting phase and different glass powders with particle size around 1 mm as the isolating phase were investigated. One glass had a density rather close to RuO 2 , the other glass significantly lower. Inks were made from RuO 2 /glass powder mixtures, a solvent, and organic additives. After manufacturing, the inks are printed on LTCC and the microstructures of the dried and the fired films were visualized by FIB preparation and SEM. The resistances as well as the temperature coefficients of the resistors were measured and compared with resistor films with an identical solid composition manufactured by conventional screen printing. The results of the obtained resistors are presented and discussed in terms of powder properties, ink dispersion, and printing parameters.

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Ink jet printable water based inks are prepared by a new silver nanoparticle synthesis and the addition of nanoscaled ZnO particles. For the formation of front side contacts the inks are ink jet printed on the front side of micro crystalline silicon solar cells, and contact the cell directly during the firing step by etching through the wafers’ anti-reflection coating (ARC). In terms of Ag dissolution and precipitation the mechanism of contact formation can be compared to commercial glass containing thick film pastes. This avoids additional processing steps, like laser ablation, which are usually necessary to open the ARC prior to ink jet printing. As a consequence process costs can be reduced. In order to optimize the ARC etching and contact formation during firing, zinc oxide nanoparticles are investigated as an ink additive. By utilization of in situ contact resistivity measurements the mechanism of contacting was explored. Our results show that silver inks containing ZnO particles realize a specific contact resistance below 10 mΩ⋅cm2. By using a multi-pass ink jet printing and plating process a front side metallization of commercial 6  ×  6 inch2 standard micro crystalline silicone solar cells with emitter resistance of 60 Ω/◽ was achieved and showed an efficiency of 15.7%.