Localized Laser Printing and Sintering of Silver Nanoparticles for Silicon Solar Cell Metallization

Metallization plays a very important role in fabricating low cost and high efficiency silicon solar cells. Silver (Ag) metallization of industrial crystalline silicon (c-Si) solar cells comprises a large share of the total cell production cost. However, in amorphous silicon based (a-Si:H) c-Si heterojunction solar cell (SHJ) fabrication, the metallization process costs more compared to the metallization process for traditional crystalline silicon (c-Si) solar cells since it requires expensive, low temperature Ag pastes [1]. These specialized, low temperature Ag pastes are required because the passivation quality at the a-Si:H(i)/c-Si interface degrades if annealed at temperatures above 200°C. This temperature limitation not only increases the fabrication cost, but also results in poor sintering of the metal contacts which increases the resistive loss [2]. In this work, we introduce a novel Ag metal contact printing technique for SHJ solar cells using a Ag nanoparticle ink and an in-line laser sintering process with the goal of reducing the bulk resistivity of the printed Ag without requiring any ex situ annealing. In this process, the Ag nanoparticle ink is dispensed through a very small diameter needle on the SHJ substrate with simultaneous sintering using a focused continuous carbon dioxide (CO
2
) laser beam. We have been able to print Ag lines with width as low as 50 µm and bulk resistivity as low as 8 µΩ·cm using this printing technique.