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

A novel approach involving CO2 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 CO2 plasma treatment pressure was preferred for the formation of oxygen-richer components in the silicon oxide films, with Si2+, Si3+, and Si4+ 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 cm2 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.