Scientists have created a transparent coating that can cool down solar cells and allow them to convert more photons into electricity.
A long-standing hurdle for the solar industry has been that the hotter a solar cell gets, the less efficient it becomes, Stanford University reported. This newly-developed patterned silica material could finally help solve the problem when laid atop a solar cell. The transparent material allows visible sunlight through to be converted into energy, but also captures and emits thermal radiation as infrared rays.
"Solar arrays must face the sun to function, even though that heat is detrimental to efficiency," said Shanhui Fan, a professor of electrical engineering at Stanford. "Our thermal overlay allows sunlight to pass through, preserving or even enhancing sunlight absorption, but it also cools the cell by radiating the heat out and improving the cell efficiency."
The technology was tested on a custom-made solar absorber, which replicates the properties of a solar cell without producing electricity. The demonstration showed the coating was able to allow visible light through to the solar cell, but also cooled it down by as much as 23 degrees Fahrenheit. This means a crystalline silicon solar cell with an efficiency of 20 percent that is cooled 23 degrees would see an improvement in absolute cell efficiency of over 1 percent. The researchers believe they may be able to scale up the solar cells to commercial size by manufacturing them using nanoprint lithography.
"That's not necessarily the only way," said research associate Aaswath P. Raman, a co-first-author of the paper. "New techniques and machines for manufacturing these kinds of patterns will continue to advance. I'm optimistic."
The new material could also have applications in other outdoor devices that are exposed to sunlight but cannot overheat.
"Say you have a car that is bright red. You really like that color, but you'd also like to take advantage of anything that could aid in cooling your vehicle during hot days. Thermal overlays can help with passive cooling, but it's a problem if they're not fully transparent," said doctoral candidate Linxiao Zhu. "Our photonic crystal thermal overlay optimizes use of the thermal portions of the electromagnetic spectrum without affecting visible light. So you can radiate heat efficiently without affecting color."
The findings were published in a recent edition of the journal Proceedings of the National Academy of Sciences.
