2.1 Fabrication of SCH and SHJ solar cells
N-type (100) oriented Czochralski (CZ) silicon wafers with a thickness of 170 μm and a resistivity of 3 Ωcm were used as the substrates. After alkaline texturing, they were cleaned according to the standard RCA procedures. After cleaning, a 7 nm a-Si:H(i) passivation layer was deposited on both sides of the substrates using plasma enhanced chemical vapor deposition (PECVD). After that, a n-type nc-Si:H layer was deposited on the front of the solar cells using PECVD. An indium cerium oxide (ICO) layer was then deposited on the nc-Si:H(n+) layer using reactive plasma deposition (RPD). Ag grids were screen printed on the front side and the semi-finished solar cells were annealed at 200 oC for 10 min. Next, a 10 nm MoOx film was deposited on the rear side using HWOSD and then an ICO film was deposited on the MoOx layer by RPD. At last, silver electrode was thermal evaporated on the whole rear side to finish the fabrication of the SCH solar cells. It should be pointed out that it is critical to carry out the screen printing process before the MoOx deposition, otherwise the performance of the SCH solar cells will be significantly reduced. The conventional SHJ solar cells were fabricated for a reference. Except for the replacement of the MoOx layer by a 15 nm p-type amorphous silicon (a-Si:H(p+)) layer, other processes and parameters are the same as that of the SCH solar cells. The photographs and the structural schematic diagram of the MoOx/c-Si(n) SCH solar cell and the process flows of the SCH and SHJ solar cells are shown in Figure 1.