Pb-free front-contact silver pastes with SnO-P₂O₅glass frit for crystalline silicon solar cells

We developed a new Pb-free Ag paste with a [Formula presented]2O5glass frit for front contact electrodes of crystalline silicon solar cells. First, we synthesized [Formula presented]2O5glass frits with various compositions, whose glass transition temperatures were 225–245 °C, by using a melt-quenching method. It was experimentally verified that the glass component SnO etched through the silicon nitride anti-reflection coating on the Si emitter. Then, four kinds of Ag pastes with various [Formula presented]2O5glass frits were prepared, screen-printed on a Si emitter, and fired to fabricate solar cells. The composition of the [Formula presented]2O5glass frit affected the surface and interfacial morphology and microstructure of sintered Ag grids, which played an important role in the series resistance and photovoltaic properties of the solar cells. It was worth noting that the cells fabricated with SnO-based Ag pastes revealed no glass layer at the interface between the Ag grids and Si emitter. This differed from cells fabricated with Ag pastes containing Pb- or Bi-based glass frits. The highest efficiency of 7.2% was achieved for cells fabricated with the Ag paste containing [Formula presented]2O5(mol%) glass frit at a firing temperature of 950 °C and a time of 5 min. This was because this Ag paste possessed the densest structure and lowest interfacial contact resistance.