Gettereing of metal impurities by flash lamp annealing in dirty-silicon solar cells


Gettereing of metal impurities by flash lamp annealing in dirty-silicon solar cells

Prucnal, S.; Abendroth, B.; Krockert, K.; König, K.; Henke, D.; Kolitsch, A.; Möller, H. J.; Skorupa, W.

Multicrystalline silicon has attracted considerable attention because of its high stability against light soaking. In case of Solar Grade (SoG) mc-Si the rigorous control of metal impurities is desirable for solar cell fabrication. Although ion implantation doping got very recently distinct consideration for doping of monocrystalline solar material, efficient doping of multicrystalline solar material remains the main challenge to reduce costs. To extend the application of the ion implantation technique to SoG mc-Si the diffusion of metal impurities during electrical activation of phosphorous and recrystallization of silicon has to be suppressed. Here an advanced annealing technique will be presented and explored, which allows the electrical activation of implanted elements by short time light pulse annealing. Flash Lamp Annealing in the ms-range is demonstrated here as a very promising technique for the emitter formation at an overally low thermal budget. It could be presented that FLA at 1000oC for 3 ms even without preheating is sufficient to recrystallize implanted silicon. The sheet resistance (SR) of FLA samples shows values of about 50 Ohm/sq. Especially, the minority carrier diffusion length for the FLA samples is in the range of 80 um without surface passivation. This is up to one order of magnitude higher than that observed from RTA or FA samples. This technology shows great promise to replace the conventional POCl3 –doping.

Keywords: solar cells; mc-Si; Flash Lamp Annealing; ion implantation

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Publ.-Id: 17277