After metallization of the solar cells, they are “baked” in a firing furnace to conserve the properties achieved in the production process. In this process the solar cells bend significantly. The layer of aluminum on the back of the cell and the silicon have a different thermal expansion coefficient. This means that the cell bends significantly during the production process when it is heated to approximately 700 °C in the firing process. It is therefore cooled down to approx. – 70 °C to make it flat again. The exposure time to both temperatures is critical to control the planarity of the cell.
It is important that the finished cell is planar, because it is pressed against flat glass during the lamination process. The process bend is therefore typically checked after the cells have been in the firing furnace, where the bend of the finished cell is greatest.
OD Precision sensors (displacement) are used to measure the bend of finished solar cells immediately after the “baking” in the firing furnace where bend is greatest.
OD Precision: OD5-30T05, together with amplifier unit: AOD5-P/N1, quantities: 3 sensor heads and 1 amplifier unit.
Reliable measuring of bend early on in the process reduces the breakage rate in later processes, especially when the cells are pressed against a flat glass in the following lamination process. This ensures higher quality to the customer, as tension in the cells on the finished module is avoided, which reduces on-site breakage of cells.