Effect of Ambients on Rear AI Metallization in Silicon Solar Cells

Abstract

AI rear contacts using paste in screen printed solar cells requires not only good passivation and high reflectance, but also a large process window compatible with the front Ag metallization temperature. In this study, the structural and electrical properties of the back surface field formed during the metallization process with different firing ambients were investigated. Also, the mechanism of burn-out of organic materials in AI paste was suggested. In N-2 ambient annealing condition, back surface fields were poorly formed which led high backsurface recombination velocity compared to O-2 and air ambients annealing. From the thermogravimetric analysis, it is considered that O-2 ambient enhanced the side group elimination during burn-out process. Therefore, O-2 ambient annealing rear contact showed mederated metal resistance even at the lower peak firing temperature. Over 780 degrees C, the AI bulk resistivity annealed at N-2 ambient showed the lowest values; however, over-shrinkage of AI was observed. The optimized temperature with oxygen flow shows an absolute efficiency of 19.1% in the PC1D simulation.