Ion Implantation without Mass Analysis and Laser Annealing for Fabrication of Silicon Solar Cells

Summary

The work outlined in the present report concerns the optimization of an ion incrustation technique, that is, implantation without mass separation, and pulsed YAG or continuous CO₂ laser annealing for the production of junctions on silicon. The ion incrustation process employed, developed by the Strasbourg CRN, is based on gas discharge in a gas containing the dopant (PF₅). The machine developed includes two work stations processing the wafers continuously. The first station performs doping, while the second can perform activation annealing, e.g., by laser.

In the framework of the present contract, ion incrustation and pulsed laser annealing were applied to the production of mono-crystalline silicon solar cells. The photovoltaic efficiencies obtained were up to 13.3% AM1 on active areas of 10 cm². These performances can be compared with those attained by cells manufacturing by ion implantation with mass separation and YAG laser annealing. The process designed was subsequently applied to polycrystalline silicons: efficiencies better than 10% AM1 were achieved. The results show the advantages of ion incrustation, which is a more simple and inexpensive technique than traditional ion implantation.

From a production point of view, pulsed annealing laser machines are already available but their throughputs are not yet compatible with a mass production. On the contrary, high power CO₂ lasers may be considered to meet this goal. For this reason, continuous CO₂ laser annealing is presently studied and promising results have been obtained on solar cells. The work in progress concerning this technique is also reported.