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

A detailed investigation of quality enhancement techniques, such as PECVD SiO2/SiN deposition and forming gas anneal (FGA) for defect passivation, and Al treatment for defect and impurity gettering, was conducted 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 upon the multicrystalline material. Besides bulk and surface defect passivation, PECVD coatings were also found to be very effective in passivating phosphorus diffused emitters. Al gettering in multicrystalline Si showed a significant improvement in bulk lifetime and Light Beam Induced Current (LBIC) response. FGA in conjunction with Al treatment resulted in an additional improvement in bulk lifetime in certain materials. Solar cells fabricated on EFG sheet Si showed an efficiency improvement 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 cast Si from Sitix corporation, using optimized gettering and passivation techniques, gave record high multicrystalline Si efficiency of 17.8%.