Screen printing and electrical properties of silver paste using a robust biopolymer binder for fine line electrode in energy devices

The purpose of this study is to identify factors affecting the dispersion and printing properties of pastes that are required to form fine line width electrodes by controlling the rheological properties of pastes applied in various fields. In particular, to solve the problem of high cost and low efficiency of silver used in the front electrode of silicon solar cells, it is necessary to print uniform fine lines with high aspect ratio to achieve higher efficiency while reducing raw material consumption. In this study, ethyl cellulose (EC), a conventional general-purpose binder, and xanthan gum (XG), which is widely used as a thickener in the food industry and has excellent temperature stability and the advantage of having a high viscosity even with a small content, used as binders. An organic solution was prepared by completely dissolving the binder in a solvent, and then inorganic particles and glass flecks were added to prepare the final paste. The rheological properties of the paste were measured, and the aspect ratio and the electrical conductivity of the electrodes were assessed after screen printing and firing. The results indicated that the paste prepared with XG binder exhibited a higher overall viscosity compared to the paste with EC binder and demonstrated a superior shear-thinning behavior. The pastes with optimal printing properties were found to contain 12 wt% EC and 7 wt% XG, respectively. In the frequency sweep test, XG had higher G' and G'' than EC, showing relatively good sedimentation stability and high aspect ratio. Viscosity recovery through hysteresis test was also better for XG than EC. For the final electrical conductivity, both EC and XG showed a value of 10³ Ω⋅m order. However, if the electrodes were formed from a paste made of XG, the final solar cell efficiency is expected to be higher due to the larger area receiving sunlight due to the high aspect ratio.

Graphical Abstract

This study investigates the rheological properties of pastes formulated with ethyl cellulose and xanthan gum for screen-printed electrodes in silicon solar cell fabrication. Xanthan gum-based pastes exhibit higher viscosity and better shear thinning behavior compared to ethyl cellulose-based pastes, with optimal printing properties observed at 7 wt% xanthan gum content. The findings suggest that utilizing xanthan gum-based pastes could lead to higher efficiency in silicon solar cells due to the potential for achieving larger aspect ratio electrodes