Hot-wire chemical vapor deposition of silicon nitride for multicrystalline silicon solar cells

A new regime of high rate deposition of silicon nitride by hot wire chemical vapor deposition was investigated. The present design of the filament arrangement and the showerhead gas supply system allows for virtually unlimited scale-up. The deposition rates obtained were in excess of 5 nm/s. The refractive index (n at 2 eV; wavelength ∼630 nm) could be controlled from 1.90 ± 0.05 to 2.5 ± 0.05, by varying the SiH₄ flow and the extinction coefficient (k) at 3.1 eV (wavelength 400 nm) was < 0.007 for all films of interest. The layers were tested on multicrystalline silicon solar cells in order to assess their passivation and antireflection properties. The cells had state-of-the-art values for all photovoltaic parameters, similar to cells with a microwave plasma deposited SiN_x anti-reflection coating. An efficiency of 14.3% was reached using HWCVD-SiN_x for multi-crystalline Si solar cells with an industrial process using screen printing.