Unification of Rheology of Thixotropic Yield Stress Fluids and Screen Printing Properties of Pastes

Abstract

Screen-printed metallization has a crucial impact on the power conversion efficiency (PCE) of solar cells. At present, the electrode width of solar cells is already less than 20 μm. Ensuring its morphology and aspect ratio is one of the main challenges to further reducing the electrode width. As the medium of paste, organic carrier plays a vital role in the rheological properties and printability of paste. In this study, combined with the wettability of the solvent to the silicon wafer, the solubility to the binder and the boiling point, the selection method of the mixed solvent for the organic carrier was given. The rheological properties of the organic carriers were measured and the Herschel-Buckley model was introduced to characterize their flow behavior. Moreover, the model parameters were unified with printability of paste, the organic carrier model parameters corresponding to the paste with good printability were contributed. The results showed that when the consistency index (K) was 21.883 and the exponent (n) was 0.1545, the aspect ratio of the electrode was the largest. When the yield stress (5.3 Pa) and thixotropic loop area (707.71 Pa s-1) were the largest, the morphology of the electrode was the most regular.

Keywords: Organic carrier, Rheological Properties, Fluid flow model, TOPCon, Ag/Al paste, Screen printing