- Heraeus extends its solar business from cell metallization pastes to crucible coatings
- Its new solution called HeraGlaze is a SiO2-barrier coating
- The coating enables extracting 4% more wafers from an ingot
- Heraeus also promising quality improvement of silicon, resulting higher efficiencies
German company Heraeus, well known for its metallization paste in the PV industry, has stepped into another business related to solar. At the International Photovoltaic Power Generation Expo (PV Expo) in Japan, Heraeus has announced that it is now offering a coating material for quartz crucibles, especially used for making multicrystalline ingots. This special coating is called HeraGlaze, which according to Heraeus is a high purity and high density SiO2-barrier coating. This coating actually prevents impurities diffusing from crucible into the silicon melt.
Apart from the silicon raw material itself, crucibles are the main source of impurities in the silicon crystal. This is more pronounced in case of multicrystalline ingot making, because throughout the process of multicrystalline ingot making – melting to solicitation – the silicon melt is contact with the crucibles. This actually leads to the diffusion of impurities from the crucible into smelt.
A coating acts as a barrier between the smelt and crucible walls. A general practice is to employ a silicon nitride coating as barrier. Companies like GT Solar offered coating solutions to ingot makers. Then, leading crucible suppliers, like Vesuvius and Ceradyne, have been offering pre-coated crucibles, which are ready for use.
Still diffusion of impurities is inevitable, which is why a layer of silicon around the multicrystalline ingot that is in contact with the crucible is removed before extracting wafers from it. According to Heraeus, its coating reduces the silicon waste to a level that enables producing 4% more wafer per ingot.
Not just the quantity, the coating is also expected to improve the quality. Heraeus says its coating also contributes to the improvements in cell level efficiency. The HeraGlaze is coating is compatible with all commercially available crucible brands.