Conveyor furnaces for metallization of c-Si solar cells. Firing of metallization paste.
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Most solar cells which are used today are based on crystalline silicon. The silicon can be mono-crystalline or poly-crystalline. Monocrystalline material is produced by the Czrochalski-process, while polycrystalline material is usually prepared by molding. In both cases the generated material is cut to wafers by wire saws. The wafers serve then as substrate material for the solar cell.
The solar cells consists mainly of silicon and is called therefore thick film solar cell, in contrary to thin film solar cells where the semiconductor layers are deposited on substrate of a different material. The bulk silicon is usually lightly p-doped, and conductive for positive charge carriers or holes. On the front side a thin heavily n-doped layer has to be formed by doping, which is conductive for negative charge carriers or electrodes. This way a p/n-junction is formed, which can separate the charge carrier pairs, generated by the absorption of sunlight. On the front side and on the back side metallic contacts have to be formed in order to drain the solar current. At the backside a holohedral aluminium layer is deposited, while at the front side silver contact fingers are generated, which allow most of the sunlight to pass into the cell. Finally a silicon nitride antireflection coating ARC is attached to the front side in order to increase absorption of the sunlight. The last production step is the assembly of the solar cells to solar modules.
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For the formation of the front side and back side contacts, metallization paste is printed on the silicon wafers, using thick film technology and screen printing. The paste is containing aluminium for the back side contact and silver for the front side contact fingers. The pastes have to be fired then in a furnace. In the debindering zone of the furnace, organic or polymer parts of the paste decomposite. In the firing section of the furnace metallic parts are sintered and form a continuous and conductive layer. For this process, a standard Koyo conveyor furnace model 47-MT with a mesh belt transportation system can be used.
For research and development, Koyo can offer a small type conveyor furnace model 810, which is constructed similar to the large furnaces and can simulate a production environment.
However Koyo developed especially for applications in the solar industry a special conveyor furnace, which
Koyo Thermo Systems and Crystec will be pleased to engineer a cost effective system to satisfy your most demanding and exacting requirements.