A New Ag-pastes were developed for integrating the high efficiency mono-Si solar cell. The pastes were the mixture of 84 wt% Ag, 2 wt% glass frit, 11 wt% solvent of buthyl cabitol acetate, and 3 wt% additives. After fabricating the Ag-pastes by using a 3-roll mill, they were coated on a $SiN_x$/n+/p- stacks of a commercial mono-Si solar cell. And the post-thermal process was also optimized by varying the process conditions of peak temperature. The optimized solar cell efficiency on a 6-inch mono-Si wafer was 18.28%, which was the one of the world best performances. It meaned that the newly developed Ag-paste could be adopted to fabricate a commercial bulk Si solar cell.