Glass phase alignment in front side pastes for P- and N-type solar cells
Using an in-situ contact resistance measurement silver pastes containing glass and aluminum additions for p- and n-type cells were investigated during rapid thermal process (RTP) firing. The glass viscosity, i.e. the formation of a liquid phase having a viscosity between 104 PaBLs and 105 PaBLs, is the crucial point for opening of the antireflection coating, regardless of the kind of wafer or aluminum addition. The maximum efficiency is obtained in an optimum between the competing effects silver precipitation and emitter corrosion and can be precisely time-resolved observed by an in-situ contact resistance measurement. The peak firing temperature determines the intensity of the interface reaction whereas the temperature related glass viscosity is crucial important for the reaction duration and acts as kinetic switch. In comparison to common pastes for p-type cells, in pastes with alumina additions for n-type cells the glass phase rearranges and depletes at the interface due to thermodynamic reasons. The rearrangement of the glass phase attenuates the reduction of silver in the interface layer and controls the solar cell contacting.