Influence of the solar cells metallization firing treatment on carrier recombination and trapping in copper contaminated multicrystalline silicon: new insights into the role of the phosphorus-rich layers

The influence of superficial phosphorus-rich layers during the metallization firing treatment on carrier recombination and trapping in copper contaminated multicrystalline silicon was investigated. Copper contaminated wafers experienced firing steps with and without phosphorus-rich layers. The samples fired without phosphorus emitters feature higher bulk carrier lifetimes, but also a stronger sensitivity to the copper-related light-induced degradation (LID), which was activated by the firing treatment. This last behavior could be used to identify the dominant LID mechanism (boron-oxygen related or copper related) in multicrystalline wafers. In addition, only the samples fired without the phosphorus emitters are subjected to trapping effects, probably involving copper atoms initially precipitated. Copper precipitates are virulent recombination centers whereas the electrical activity of interstitial copper is benign. Therefore these experimental results suggest that on the one hand the wafers fired with the phosphorus-rich layers contain lower interstitial copper concentrations. On the other hand they would feature higher densities of copper precipitates and/or larger copper precipitates.