In Situ Process to Form Passivated Tunneling Oxides for Front-Surface Field in Rear-Emitter Silicon Heterojunction Solar Cells

Abstract

A novel approach involving CO 2 plasma treatment of intrinsic hydrogenated amorphous silicon was developed to form ultrathin silicon oxide (SiO x ) layers, that is, passivated tunneling layers (PTLs), for the fabrication of passivated tunneling contacts. These contacts were formed by depositing the PTL/n-type hydrogenated nanocrystalline layer (nc-Si:H(n))/ c-Si(n) stacks. The results indicated that a higher CO 2 plasma treatment pressure was preferred for the formation of oxygen-richer components in the silicon oxide films, with Si 2+ , Si 3+ , and Si 4+ peaks, and a smoother PTL/c-Si heterointerface. The PTLs with higher oxidation states and lower surface roughness exhibited advantages for the c-Si surface passivation, with a maximum implied open-circuit voltage of approximately 743 mV. The lowest contact resistivity of approximately 60 mΩ cm 2 was obtained using nc-Si:H(n)/PTL/c-Si(n) as the passivated tunneling contact. Most importantly, the in situ process can help prevent the contamination of the heterointerface during device fabrication processes.

Surface Cleaning and Passivation Technologies for the Fabrication of High-Efficiency Silicon Heterojunction Solar Cells

“…A significant advantage of such dry etching in manufacturing is that both surface cleaning (the last step) and deposition can be performed in the same system without interrupting the vacuum, thereby avoiding the risk of re-oxidation and recontamination [58,59]. However, the optimal trade-off between effective plasma cleaning treatment and preservation of undamaged silicon surfaces requires further investigation [57].…”