Wafers For Solar PV
Gas Recovery and Recycle Limited, GR2L, has developed a unique, closed loop, argon purge gas recovery and purification system, the ArgonØ, to recycle the high purity argon purge gas used in the fabrication of Silicon wafers for Solar PV applications.
High purity argon (better than 99.9998%) is used as a shield gas in the production of silicon ingots, to be fabricated into wafers, for solar cells and micro-electronic devices. The argon is used to control the gaseous impurity levels present during the manufacturing process to an acceptable level. In response to the trend in the solar industry for yet higher efficiency solar panels the argon purge gas flows used in the CZ Ingot Pullers have increased by up to 100% in the last 5-10 years with current purge flows in the 80-100 l/min range – higher purge gas flows translate directly into silicon wafers with fewer defects and improved carrier lifetimes resulting in solar cells with improved efficiency.
The supply of high purity argon is primarily a by-product of the air separation process generating oxygen used in steel making. This means, at best, the supply of high purity argon is essentially fixed and at worst in shortening supply as air separation units are moth-balled in line with reducing steel manufacturing capacity. The laws of “supply and demand” dictate that the argon price will increase. This is precisely what is being seen in the market, with argon prices increasing by as much as 50% in the last couple of years in some territories even during the Covid-19 pandemic.
There is also a growing requirement for all elements of the Solar PV supply chain to reduce their carbon footprint with some geographies and energy companies, for example in Europe, moving to only approving panels for sale and installation with a low manufactured carbon footprint. After the electricity used to directly heat the CZ ingot pulling furnaces the carbon footprint associated with the purchase of high purity liquid argon, for the inert purge gas, contains one of the highest CO2 equivalent footprints.
For manufacturers faced with this “triple whammy” of increasing argon usage, rising argon prices and having to reduce their CO2 footprint, investing in the Gas Recovery and Recycle Limited ArgonØ argon recycling systems, which can reduce the facility argon usage by at least 95%, is a highly attractive proposition saving both cost and CO2 footprint and improving sustainability.
The exhaust gas from a CZ puller furnace is typically contaminated with predominantly carbon monoxide and hydrogen in the 300 to 3,000ppm range along with lower levels of moisture and carbon dioxide although levels up to 6,000ppm of these contaminants can be seen during the recharge process. These gases primarily originate from reactions of moisture and silicon monoxide with process chamber components such as the heaters and insulation. The ArgonØ effectively removes these impurities to below 1ppm at recycle rates of at least 95%.