Defect passivation in multicrystalline-Si materials by plasma-enhanced chemical vapor deposition of SiO2/SiN coatings

It is shown for the first time that plasma-enhanced chemical vapor deposition (PECVD) passivation which involves low temperature PECVD of ∼100 Å SiO2 and ∼600 Å SiN followed by photoassisted anneal is very effective for both surface and bulk defect passivation in multicrystalline-Si materials. It is found that the effective recombination lifetime increased by a factor of 2–10 depending upon the multicrystalline material. Some solar cells were fabricated using a three-layer PECVD coating (100 Å SiO2/600 Å SiN/950 Å SiO2), the bottom two for passivation and the top two for antireflection coating. The bulk and surface passivation effects were quantified and decoupled by a combination of internal quantum efficiency measurements and computer modeling. It was found that the PECVD passivated solar cells increased bulk lifetime from 10 to 20 μs, and decreased the surface recombination velocity from 2×105 to 5×104 cm/s.