Exploring the performance and reliability of screen-printable fire-through copper paste on PERC solar cells

In this work, we present the performance and reliability of a fire-through copper (Cu) paste which has been screen printed on c-Si solar cell with passivated emitter rear contact (PERC). The Cu paste is fired through silicon nitride (SiN) anti-reflection coating at a peak temperature of $630^{\circ}\mathrm{C}$. SEM images of the Cu paste show a Cu core with ~200 nm oxide shell around the particles. This conductive oxide layer acts as a diffusion barrier between Cu and Si and prevents the degradation of cell performance during accelerated aging conditions. An efficiency of 19.250% has been achieved with $\mathrm{V}_{\mathrm{o}\mathrm{c}}=654\text{mV}, \text{FF}=$ 76.68%, $\mathrm{J}_{\text{sc}}=38.40$ m.A/cm²for champion PERC cells. Accelerated testing of the PERC mini-modules in damp heat chamber with $85^{\circ}\mathrm{C}$ and 85% humidity have demonstrated that the devices are operational even after 1,500 hours. Devices with screen printed Ag contacts on the front side have been studied in parallel to the Cu contacts for comparison.