Effect of TeO2-based lead-free glass on contact formation of front side silver metallization for monocrystalline silicon solar cells

TeO 2 –Bi 2 O 3 –ZnO–Li 2 O–MgO lead-free glass was synthesized based on the consideration of environmental protection and the demand for further conversion efficiency improvement. Reactivity of Bi 2 O 3 powder with SiN x and Si as well as lead-free glass with SiN x and Si was investigated using differential thermal analysis. DSC curves show that Bi 2 O 3 doesn't react with SiN x or Si under 800 °C, whereas lead-free glass can react with SiN x and Si at approximately 600 °C indicating early softening and melting of glass facilitates the reaction between Bi 2 O 3 and SiN x or Si. The flowing behavior of lead-free glass at varied temperatures was studied and the morphology of the interface between the glass and the silicon wafer was examined. The white particles formed above silicon were identified as Bi–Te alloy or BiTeO x through stoichiometrically calculating. However, their formation was suppressed by the addition of silver powder. Ag crystallites and Ag particles start to generate on the interface, as the content of silver powder was increased to 8 wt%. These Ag particles and Ag crystallites were observed on the interface in the finished solar cell. • TeO 2 -based lead-free glass could replace leaded glass in silicon solar cells. • Bi–Te alloy or bismuth tellurite forms at the glass/Si wafer interface. • Addition of silver powder suppresses forming of Bi–Te alloy or bismuth tellurite. • Ag crystallites and Ag particles generate as more silver powder is added. • Ag crystallites and the glass layer play a decisive role in the contact formation.