Solar cells suffer a strange problem: the hotter they get as the sun pours down on them, the less efficient they become at converting light into electricity. But now a team of Stanford researchers have developed a new transparent coating that can help them keep a little cooler — and more efficient.
The new coating is based on a simple idea: When you step outside, the top of your head radiates (at least a little) heat up into the universe as infrared light. The new coating, described in Proceedings of the National Academy of Sciences, uses the same idea to help solar cells quickly shed heat.
The material is a relatively simple film of thin, patterned silica, which can be laid down on top of a normal solar cell. The sheet is transparent to the visible light which drives solar cells, but it absorbs — and crucially emits — thermal radiation in the form of infrared rays. So essentially it sucks heat from the solar cell and pumps it out into the atmosphere, helping lower the temperature of the device. The technology is based on a previous coating developed by the group, which both reflected sunlight and radiated heat.
In tests performed atop a Stanford roof, the team showed that the film allowed visible light to pass through but reduced the temperature of the cell beneath by up to -5 degrees Celsius. For a fairly normal crystalline silicon solar cell with 20 per cent efficiency, the researchers claim that sort of temperature reduction could equate to an increase in the absolute cell efficiency by over 1 per cent — not to be sniffed at if the film can be made affordably.
No wonder, then, that the team is now working to develop lithography techniques that can be used to generate the film at a commercial scale.
Image by Michael Shealy under Creative Commons licence.