HiPIMS deposition of silicon nitride for solar cell application

Silicon nitride (SiNx) and hydrogenated silicon nitride (SiN:H) thin films were deposited by reactive High Power Impulse Magnetron Sputtering (HiPIMS), at room temperature, in argon, nitrogen and hydrogen gas mixture. The long-term aim of our research is to obtain coatings for solar cell application, with improved optical properties, in a wide range of wavelength radiation. Anti-reflection, passivation and wear resistance properties are also considered for space mission application. Optical, compositional, structural, mechanical and tribological properties of the deposited films were characterized by UV-Vis-NIR spectroscopy, Glow Discharge Optical Emission Spectrometry (GDOES), thermal desorption spectroscopy (TDS), Fourier transform infrared (FTIR) spectroscopy, atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray diffraction (XRD), nanoscratch and nanoindentation. The obtained coatings show dense amorphous and amorphous to nanocrystalline structure, high packing density, very low surface roughness and very good adhesion to substrate and wear properties. Optical properties were optimized to obtain films of low effective reflectivity in a broad-band wavelength range, with good passivation properties and enhanced mechanical and tribological properties. The average reflectance measured in the range of 200-1800 nm is less than 5%, while the average transmittance is up to 93%. GDOES and TDS measurements of SiN:H coatings revealed a diffusion process of atomic H into the Si substrate. FTIR analysis of SiN:H films indicated the presence of numerous hydrogen bonds (Si - H and N - H) which could passivate structural defects and reduce the number of recombination centers in silicon bulk.