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.