The effects of nano Ag particles on gridline sintering for silicon solar cells

Achieving high fill factor (FF) for industrial silicon solar cells relies on metallization process through Ag paste. The rheology of the paste has an impact on overall performance because it affects printability. It is reported in this paper that adding different organics to the paste provides ~0.2% efficiency gain due to decreasing metal coverage. Also, sintering process of Ag particles in the paste is critical for contact and gridline resistances. The impact of Ag sintering on the gridline and formation of Ag crystallites and thin glass layer at the Ag/Si interface are discussed in detail. The porosity of fired contacts and hence gridline resistance can be reduced by using nano Ag particles in the paste, while contact resistance can also benefit from nano particles through formation of uniform Ag crystallites and a thin (~0.1nm) glass layer. It is also reported that firing time (or belt speed) also determines the kinetics of sintering by decreasing dwell time down to ~2s. Increasing the belt speed up to 350ipm results in the increase of 2.8% and 3.9% in fill factor for mono and multi crystalline silicon solar cells respectively.