Room temperature surface passivation of silicon for screen printed c-Si solar cells by HiTUS reactive sputter deposition

The dielectric coatings used on silicon solar cells serve a dual purpose: a surface passivation layer and as an antireflection coating. Silicon nitride films were deposited by sputtering, using a HiTUS technology, on crystalline silicon wafers. Films were deposited without substrate heating, which simplifies the deposition process, from a polycrystalline silicon target in a mixed ambient of argon, nitrogen and hydrogen gasses. After the deposition, the minority carrier lifetime, refractive index and deposition rate were measured. Photo conductance decay measurements show that the minority carrier lifetime increased up to 26 μs on a 40 Ω/□ doped 1 Ω cm p-type 〈1 0 0〉 Cz-Si pseudo square wafer (compared to 1 μs measured for bare wafer) and up to 984 μs for a double-side polished 3 Ω cm Cz-Si wafer (from ∼70 μs measured for uncoated wafer). Spectroscopic ellipsometry measurements showed that the refractive index of the deposited films was 2.05 at λ = 632.8 nm; deposition rate was measured at 22.4 nm/min. The films were used to prepare screen-printed c-Si solar cells. The resultant cells showed an efficiency of 15.14% with silicon nitride films grown without the use of silane or substrate heating.