Attenuation of short-circuit effect along screen-printed silver gridlines during the contact firing process of crystalline silicon solar cells

초록

The "short-circuit effect" in the fire-through Ag metallization of crystalline Si (c-Si) solar cells refers to the poor contact formation caused by an electrical short between the Ag gridline and underlying Si emitter during contact firing. This study employs two different Ag pastes containing PbO- and TeO2-based glass frits to investigate the dependence of the short-circuit effect on the length and pattern of the Ag finger lines. The results show that regardless of the employed glass frits, the short-circuit effect is mitigated even near the short spot and gradually attenuated along the finger line away from the spot as the Ag finger line extends radially longer than the critical length (>35 mm). We demonstrate that this attenuation is independent of the finger line width and predominantly attributed to the ohmic drop of the electrode potential along the Si substrate. The results also show that, regardless of the glass frits, the contact quality is strongly correlated with the density of the Ag crystallites that are formed on the Si emitter surface. The 6-in full-cell tests indicate that the isolation of the short spots by segmenting the Ag finger lines does not necessarily result in the mitigation of the short-circuit effect. We suggest that the reduction of Ag+ on the Si emitter surface should be the key process that must be controlled to achieve high-quality contacts during contact firing, providing further insights into the electrochemical characteristics of contact firing reactions for the future development of Ag pastes.

키워드