Hydrogen-Assisted Defect Engineering of Doped Poly-Si Films for Passivating Contact Solar Cells

Hydrogen-assisted defect engineering, via a hydrogenated silicon nitride (SiN_x:H) capping layer, on doped polycrystalline silicon (poly-Si) passivating-contact structures, is explored using complementary techniques. The hydrogen treatment universally improves the passivation quality of poly-Si/SiO_x stacks on all samples investigated. Meanwhile, their contact resistivity remains very low at ∼6 mω·cm². Moreover, the nature of charge carrier recombination within the poly-Si films is also investigated by means of photoluminescence. On planar c-Si substrates, the poly-Si films emit two broad photoluminescence peaks at ∼850-1050 and ∼1300-1500 nm. The former is the characteristic peak of the hydrogenated amorphous Si (a-Si:H) phase and only appears after the treatment, demonstrating that (i) a significant amount of hydrogen has been driven into the poly-Si film and (ii) an amorphous phase is present within it. The second peak originates from sub-band-gap radiative defects inside the poly-Si films and increases after the treatment, suggesting a suppression of their nonradiative recombination channels. For films deposited on textured c-Si substrates, there is a disrupted oxide boundary, preventing a buildup of excess carriers inside the films and leading to quenching of the film luminescence.