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22 Sep 2004
A low-cost, anti-reflective, anti-fog coating could boost the performance of solar cells, spectacles and car windows.
Australian researchers are busy commercializing a low-cost, hard and permanent anti-reflection surface coating that is set to boost the collection efficiency of solar cells by up to 8%. Dubbed 'XeroCoat', its anti-fog properties could also benefit spectacles and car windscreens.
Most solar cells contain a glass plate protecting the photovoltaic material from the environment. Anti-reflection coatings help to boost the transmission of incoming light by reducing reflections at the plate's air-glass interfaces.
"It is cost that has been preventing this," XeroCoat's Michael Harvey told Optics.org. "Vacuum deposited anti-reflection coatings are too expensive in all but the most high-end applications, for example aerospace and defence." Being low-cost, the team believes that XeroCoat is the perfect solution for coating large areas such as solar collector surfaces.
XeroCoat is effectively mesoporous silica, a thin layer of glass riddled with tiny holes. This gives the coating a large surface area (greater than 300m2/g) and a refractive index that can be as low as 1.28.
"The coating process is remarkably simple and quite inexpensive," said Harvey. "It is a liquid process and we believe that it could be added into current manufacturing lines with relative ease." The process is carried out at room temperature and pressure, avoiding the use of expensive kit such as vacuum chambers or pressure vessels.
XeroCoat was invented by Harvey at the University of Queensland in 2001. Targeting solar cell applications, Harvey and his colleague Paul Meredith thought it would be a great idea to launch the process as a single layer quarter-wave broadband anti-reflection coating. Queensland's Sustainable Energy Innovation Fund agreed and recently awarded the team a AUD121 000 grant to help scale-up the process.
"We are currently constructing a demonstration coating plant to produce sample solar cells for testing," revealed Harvey. "This should be ready by the end of 2004 and we should be testing our first cells by March 2005."
Preliminary data from single side coatings on glass show an increase of around 3% in transmission, and in principle XeroCoat could ultimately reduce reflection losses by up to 8%.
However, even if the solar cell market doesn't take off Xerocoat still looks poised for success. The coating can be applied to many surfaces including glass and plastics, and its anti-fog properties would certainly benefit products such as spectacles, car windscreens or swim and ski-goggles.
"The anti-fogging effect is achieved by water being drawn into the pores as it condenses on the coated surface," explained Harvey. "It [water] is prevented from forming droplets and so the condensed water does not scatter light and the user does not see fogging of the surface."
Author
James Tyrrell is reporter on Optics.org and Opto & Laser Europe magazine.
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