Screen printable copper pastes for silicon solar cells

The current work demonstrates the successful metallization of a PERC silicon solar cell with screen-printable copper (Cu) paste that is sintered at elevated temperature in air atmosphere. The existing state of the art in Silicon (Si) solar cell metallization is silver (Ag) paste; Cu cost is 1/100th the cost of Ag and has a comparable conductivity. However, Cu undergoes rapid oxidation at elevated temperatures and the high diffusion of Cu into Si restricts its usage in the metallization of silicon solar cells. In this paper, a Cu paste containing a proprietary mixture of antioxidant additives and diffusion inhibitors was used to make front gridlines on PERC cells. The Cuprinted cells were fired in an IR belt furnace with a peak temperature of 576 degrees C in air atmosphere. The solar cells discussed here reached an efficiency of 19%, which is 88% of the efficiency measured for a commercial Agprinted cell. The working devices were further characterized using STEM, EDX, ToF-SIMS and long-term sunsVoc studies demonstrating an absence of Cu diffusion. Furthermore, thermally stressing the Cu-printed solar cells yielded a reduction of less than 1.9% of the initial pseudo fill factor (pFF) after 1000 h at 200 degrees C. The shunt resistance of cells monitored over 3 years remained within 2.5% of its initial value, which demonstrates the effectiveness of the Cu diffusion barrier.

Automated summary

This study demonstrates the successful metallization of a PERC silicon solar cell using screen-printable copper (Cu) paste. The Cu paste contains antioxidant additives and diffusion inhibitors to prevent oxidation and diffusion of Cu. The Cu-printed cells achieved an efficiency of 19% and showed no Cu diffusion after characterization tests. The long-term stability and effectiveness of the Cu diffusion barrier were also confirmed.