Optimised antireflection coatings for planar silicon solar cells using remote PECVD silicon nitride and porous silicon dioxide

Abstract

Silicon nitride (SiN) films fabricated by remote plasma-enhanced chemical vapour deposition (RPECVD) have recently been shown to provide an excellent electronic passivation of silicon surfaces. This property, in combination with its large refractive index, makes RPECVD SiN an ideal candidate for a surface-passivating antireflection coating on silicon solar cells. A major problem of these films, however, is the fact that the extinction coefficient increases with increasing refractive index. Hence, a careful optimisation of RPECVD SiN based antireflection coatings on silicon solar cells must consider the light absorption within the films. Optimal optical performance of silicon solar cells in air is obtained if the RPECVD SiN films are combined with a medium with a refractive index below 1·46, such as porous SiO2. In this study, the dispersion of the refractive indices and the extinction coefficients of RPECVD SiN, porous SiO2, and several other relevant materials (MgF2, TiOx, ZnS, B270 crown glass, soda lime glass, ethylene vinyl acetate and resin as used in commercial photovoltaic modules) are experimentally determined. Based on these data, the short-circuit currents of planar silicon solar cells covered by RPECVD SiN and/or porous SiO2 single- and multi-layer antireflection coatings are numerically maximised for glass-encapsulated as well as non-encapsulated operating conditions. The porous SiO2/RPECVD SiN-based antireflection coatings optimised for these applications are shown to be universally suited for silicon solar cells, regardless of the internal blue or red response of the cells. Copyright © 1999 John Wiley & Sons, Ltd.