Modelling c-Si/SiNx interface recombination by surface damage

Amorphous silicon nitride (SiNx) layers are widely used for the electronic passivation of surfaces in Si solar cells. However, measurements have consistently shown that the effective recombination velocity Seff increases with decreasing excess carrier density Δn < 1015 cm–3 at acceptor densities below 1017 cm–3. This poor performance is not observed at surfaces diffused with dopants, which requires an additional high temperature process during cell fabrication. Understanding the poor performance at low Δn may therefore provide strate gies for cost reduction in solar cell processing. This paper presents a detailed quantitative analysis of this effect. It is concluded that the lifetime is reduced to a value near 1 μs in a 100–500 nm thin region underneath the SiNx layer. We predict, that to avoid this effect, a mere tenfold reduction of the density of defect states in this region is sufficient. A possible explanation of this effect are defects caused by H-termination during wafer pretreatment. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)