Hydrogen passivation of polycrystalline silicon solar cells by plasma deposition of silicon nitride

Plasma-enhanced chemical vapor deposition (PECVD) is used for the deposition of a silicon nitride antireflection coating (ARC) onto 10×10 cm² Wacker Silso polycrystalline silicon solar cells. It is found that the short-circuit current I_sc is improved by 7 to 10% in comparison to reference cells with a standard screenprinted Ta₂O₅ coating. Part of the increase in I _sc is because of a smaller reflectivity of the silicon nitride ARC. The other part of the improvement comes from all enhanced average minority-carrier diffusion length (L_min). The increase in L_min results from hydrogen passivation and is attributed to the generation of hydrogen ions during PECVD of Si₃N₄. It is shown that the passivation effect from PECVD of Si₃N₄ is comparable to that obtained with a 1/2 h hydrogen plasma treatment and that it is stable during a 1 h anneal at 700°C. A significant influence of the substrate temperature during Si₃N₄ deposition in the range of 350 to 450°C was not observed