Characterization of TeO₂ based glass frits and morphology to their silver films

Novel Pb-free Ag paste with a TeO₂ based glass frit for front contact electrodes of crystalline silicon solar cells were prepared. The influence of TeO₂ content (44–80 mol%) on thermal properties, structure and chemical durability of TeO₂ based glass was investigated. The thermal expansion coefficient decreased firstly when the TeO₂ content reached 60 mol%, then increased with further increasing TeO₂ content. The glass transition temperatures are 400–450 °C and melting temperature was as low as 800 °C. The weight loss of Te-3 glass specimen value is 0.28 × 10⁻³ mg/cm², improving the chemical durability of the TeO₂ based glass system. In addition, morphology of TeO₂ based Ag films sintering at various temperatures were also investigated. The grain size of the Ag film increased when the content of glass frit increased, and grain boundaries for sintering TeO₂ based Ag pastes was obvious. The host elements of Ag, Te, Bi, and O in AT-3 specimens were almost homogeneously distributed. The amounts of SiO₂ formed when the Ag films were firing at 750 °C, indicating the etching of SiN_x layer by TeO₂ based glass frit. The specific resistivity of silver conducting films with 3 and 5 wt% glass materials of silver component were 3.1 and 3.7 µΩ cm, respectively.