Sulfur-Enhanced Field-Effect Passivation using (NH4)2S Surface Treatment for Black Si Solar Cells.

We demonstrated surface passivation of a black Si-based solar cell using an (NH4)2S solution to mitigate surface recombination velocity. Incorporated S at the interface between atomic-layer-deposited Al2O3 and black Si by (NH4)2S solution treatment boosted the density of negative fixed charges, S-enhanced field-effect passivation. Furthermore, NH4OH generated during (NH4)2S solution treatment removed the defective Si phase at the black Si surface, the surface cleaning effect. The optimized (NH4)2S solution treatment significantly enhanced the internal quantum efficiency up to ∼17.2% in the short wavelength region, suggesting suppressed surface recombination. As a result, photoconversion efficiency of the cell increased from 11.6 to 13.5%, by 16% compared to the control cells without (NH4)2S solution treatment.