The coating was developed by the University’s Centre for Renewable Energy and Sustainable Technology (CREST) using the same technology used for depositing anti-reflection coatings on spectacles. Each glass surface reflects about four per cent of the incident light, representing a significant loss of light into the module. The AR design, developed by Professor Walls, Dr Piotr Kaminski and Fabiana Lisco, reduces the reflection by more than 70 per cent across the wavelength range accepted by PV panels.
“They improve the module power output by about four per cent and will be low cost if manufactured in high volume” said Professor Michael Walls, one of three CREST members who came up with the multi-layer AR design. “We really want to see these AR coatings implemented by manufacturers. It’s a great added value proposition for float glass manufacturers.”
The coating consists of four alternate layers of zirconium oxide and silicon dioxide, the whole stack being less than 300 nanometres thick. These materials were chosen because of their abundance and low cost and they are deposited using magnetron sputtering by a machine developed by UK company Power Vision Ltd to deposit AR coatings on spectacles.
“The AR coating has to be cost effective and so the design is a compromise” said Dr Kaminski. “We want the best quality AR coating but with inexpensive materials and as few layers as possible. Also, the whole stack should be very thin to save time in manufacturing.”
The project was aimed specifically at improving the efficiency of thin film Cadmium Telluride solar cell devices, but the coatings can also be applied to other thin film technologies such as CIGS (copper indium gallium selenide) and amorphous silicon. They can also be applied to glass covering crystalline silicon modules and third generation devices such as organic or perovskite devices. Dr Kaminski said that although each PV technology operates in a different wavelength range, it is relatively simple to accommodate this in the multilayer design for each case.
The coatings are also scratch resistant and durable and would be suitable for a full 25 year warranty as offered by PV module manufacturers. The project was funded by the Engineering and Physical Sciences Research Council (EPSRC) Supergen SuperSolar Hub. The EPSRC is the UK’s main agency for funding research in engineering and the physical sciences and invests around £800 million a year in research and postgraduate training, to help the nation handle the next generation of technological change.
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