Silicon-based solar cells Characteristics and production processes ...

Silicon-based solar cells – characteristics and production processes
Fig. 20. System of squeegees brushing the paste over the sieve and pressing the paste
through the meshes onto the plate’s surface (left) and a sequence of paste printing in the
process of creating the front electrode with the screen process method (right).
Fig. 21. Scheme of a plate section after the deposition of consecutive paste layers with the
screen process method.
V. Thermal process of electrode metallization
After drying the paste, the plate is fired in an IR furnace, in purified natural
atmosphere or in N 2 . The actual temperature of the electrode metallization process
depends on the temperature in the particular consecutive heat zones of the furnace
and the speed of the tape transport. The temperature profile of the metallization
process must be set in such a way so that the Ag paste can penetrate the Si x N y :H layer
and create an alloy with the upper Si emitter layer of the n-type, but which can
absolutely not diffuse inside the area of the space charge. At the same time, in this
process, at the temperature of above 577 o C, Al diffuses from the paste deposited on
the rear surface of the plate, at the depth of about 5 µm, and compensates the
existing area of the n-type conductivity and the thickness of ~ 0,5 µm, changing the
conductivity type into p, with a simultaneous formation of the Al-Si alloy. A part of
the diffusing Al atoms assumes the substituting positions in the crystal Si lattice,
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