A study on the aluminum fire-through to a-SiNx:H thin film for crystalline solar cells

The relationship between aluminum fire-through and the properties of a-SiNx:H thin films was investigated to aid their use as dielectric layers in rear side and front passivation layers in crystalline solar cells. Aluminum fire-through was shown to depend on the refractive index and the deposition rate of the films.Refractive index, density and deposition rate increased with increasing SiH4/NH3 ratio, while the etching rate decreased. Aluminum fire-through occurred in a sample of refractive index 2.0 during fast deposition but not when the deposition rate was slow. Aluminum fire-through occurred during extended firing, despite it not occurring during normal firing by RTP. The results of this work demonstrate that refractive index was the major determinant of aluminum fire-through, and that the aluminum and the a-SiNx:H thin film reacted immediately at the beginning of firing at a rate determined by the deposition rate.

► Carrier lifetime increased with increasing refractive index of a-SiNX:H films.
► The ratio of Si to N in a-SiNX:H films increased with increasing refractive index of a-SiNX:H films.
► Refractive index of a-SiNX:H films was the major determinant of aluminum fire-through, and aluminum reacted with the a-SiNX:H thin films at the start of the firing process at a rate dependent on the deposition rate.