GETTERING AND PASSIVATION FOR HIGH-EFFICIENCY MULTICRYSTALLINE SILICON SOLAR-CELLS

A detailed investigation of quality enhancement techniques, such as PE CVD SiO2/SiN deposition and forming gas anneal (FGA) for defect passiv ation, and Al treatment for defect and impurity gettering, was conduct ed on several promising multicrystalline Si materials. The PECVD SiO2/ SiN coating increased the bulk lifetime by a factor of 1.3 to 1.7, and decreased the surface recombination by a factor of 5-22, depending up on the multicrystalline material. Besides bulk and surface defect pass ivation, PECVD coatings were also found to be very effective in passiv ating phosphorus diffused emitters. Al gettering in multicrystalline S i showed a significant improvement in bulk lifetime and Light Beam Ind uced Current (LBIC) response. FGA in conjunction with Al treatment res ulted in an additional improvement in bulk lifetime in certain materia ls. Solar cells fabricated on EFG sheet Si showed an efficiency improv ement of 2.6% from FGA alone, 1.5% due to Al gettering alone, and 1.2% from Al diffusion and FGA interaction. Finally, cells fabricated on c ast Si from Sitix corporation, using optimized gettering and passivati on techniques, gave record high multicrystalline Si efficiency of 17.8 %.