The new HeraGlaze protective coating increases wafer yield in solar cell production by up to 4%

technology report, March 2017

Silicon, the raw material for solar cells, is melted into ingots and then processed into wafers. During the melting process, metallic impurities form on the surface of the ingots and need to be removed. With HeraGlaze, Heraeus has developed a new coating made from high-purity silicon dioxide (quartz glass) that reduces these unwanted impurities and increases the yield of silicon wafers for solar cells by up to 4%.

Improved carrier lifetime - measured by Fraunhofer Institute

At an annual wafer production of approximately 50 gigawatts, a higher production yield using HeraGlaze results in a performance increase of approximately 2 gigawatts. A nuclear power plant has a rated output of approximately 1.4 gigawatts. HeraGlaze, therefore, promises significant efficiency boosts for renewable energies.

HeraGlaze creates added value at the very start of the wafer production chain

A series of complex production steps must first be performed before a solar cell can harvest power from the sun’s rays. The process begins with melting the silicon into ingots. Impurities form on the surface areas of the ingots during the melting process, caused by iron released by the crucible. This surface area of the ingot must be thoroughly removed, because only pure silicon can be used in the subsequent wafer production process, which costs valuable time and money.

Heraeus has developed a new coating made from high-purity silicon dioxide (quartz glass).

Now, Heraeus has introduced its HeraGlaze coating to the market, which significantly increases yield of silicon ingots. HeraGlaze is made from ultrapure silicon dioxide (quartz glass) and is a milky slurry (see photo) that is applied to the porous surface of the crucible, where it sinters into a highly compressed protective coating during the silicon melting process. This glasslike barrier prevents diffusion and reduces impurities in the ingot. The coating can be applied directly at the customer’s production site and allows for existing crucibles to be retrofitted or upgraded. This makes the solution cost-efficient, as there is no additional expense for new crucibles.