It has been demonstrated that the hydrogenated nanocrystalline silicon oxide (nc-SiOx:H) is an ideal material to replace the typically used amorphous silicon (a-Si:H) in silicon heterojunction (SHJ) solar cells to reduce the parasitic absorption in window layer and further increase the power conversion efficiency () of solar cells . However, the low deposition rate (< 0.05 nm/s) of nc-SiOx:H is a drawback, which results in a long deposition time for cell fabrication. Normally, 10~20 nm nc-SiOx:H (n) is needed in a SHJ solar cell . In this work, 5 nm ultra-thin n-type nc-SiOx:H (nc-SiOx:H (n)) deposited by plasma enhanced chemical vapor deposition (PECVD) was applied as electron transport layer (ETL) and window layer in n-type SHJ solar cells in order to reduce the deposition time. To compensate the fill factor (FF) loss due to reduced ETL thickness, a thin n-type nanocrystalline silicon [nc-Si:H(n)] was deposited upon the nc-SiOx:H(n) layer by PECVD to reduce the contact resistance with transparent conductive oxide (TCO) . The process sequence of nc-SiOx:H(n)/nc-Si:H(n) double layer was specially investigated to see its effect on cell performance. The process sequence is described as: i) turning on the generator to deposit nc-SiOx:H firstly, then extinguishing the plasma, closing the CO2 inlet and waiting it exhausted for a while, and turning on the generator again to deposit nc-Si:H(n); ii) turning on the generator for the nc-SiOx:H deposition and then start the nc-Si:H(n) deposition directly by closing the CO2 inlet. The film qualities such as conductivity and band gap measured on glasses were compared for these two sequences. Finally, both sequences were applied on SHJ solar cells and the detailed effects were discussed.