A Strategy to Optimize Nickel Oxide/Crystalline Silicon Heterocontact of HJT Solar Cells

NiO x is a p-type semiconductor material with wide band-gap (3.6 ∼ 4.0 eV), good thermal and chemical stability. In terms of energy band structure, NiO x /n-Si possesses low valence band offset to allow hole and high conduction band offset to block electron, NiO x is thus a promising hole-selective layer for n-type c-Si based heterojunction (HJT) solar cells. However, intrinsic NiO x suffers from low carrier concentration and poor conductivity, which severely limits its development in photovoltaics. This study aimed to obtain Ag-doped NiO x film with high carrier concentration and low resistivity by co-sputtering using high-purity Ag and NiO x target for high efficiency solar cells. The results show that appropriate Ag doping can increase the acceptor concentration of the film, promote the tunnelling effect, reduce interface recombination, and thus improve the device efficiency. When Ag content is 2.4%, the fill factor of Al/ITO/NiO x :Ag/SiO x /c-Si/SiO x /Al solar cell is increased from 52.97% to 68.42%, and the power conversion efficiency reaches 9.11%. Combined with the analysis of AFORS-HET simulation, the mechanism how Ag doping works in the hetrojunction is revealed.