Thin is in, from the peel-and-stick thin-film solar cells that Stanford University scientists described last year, to the super-thin, stackable solar cells MIT researchers recently conceptualized. Now Stanford is back with “the thinnest, most efficient absorber of visible light on record.”
It’s a wafer dotted with trillions of round particles of gold, nanodots about 14 nanometers tall and 17 naonmeters wide (a nanometer is a billionth of a meter).
“Achieving complete absorption of visible light with a minimal amount of material is highly desirable for many applications, including solar energy conversion to fuel and electricity,” Stacey Bent, a professor of chemical engineering at Stanford and co-author of the study, said in a statement.
The light spectrum isn’t just visible light, of course, with different waves ranging from 400 nanometers long to 700 nanometers long, but the Stanford team “tuned” its cell to absorb only visible reddish-orange light waves about 600 nanomaters long.
“The coated wafers absorbed 99 percent of the reddish-orange light,” fellow researcher Carl Hagglund said. “We also achieved 93 percent absorption in the gold nanodots themselves. The volume of each dot is equivalent to a layer of gold just 1.6 nanometers thick, making it the thinnest absorber of visible light on record – about 1,000 times thinner than commercially available thin film solar cell absorbers.”
Great stuff – but what’s the takeaway for you as a citizen of the world hoping renewable energy can rise up and slay the fossil fuel dragon?
Well, when it comes to solar cells, “This provides a benefit in minimizing the material necessary to build the device, of course,” Bent said. But there’s more.
“(T)he expectation is that it will also allow for higher efficiencies, because by design, the charge carriers will be produced very close to where they are desired – that is, near where they will be collected to produce an electrical current or to drive a chemical reaction.”
One thing that could make this breakthrough more viable is reliance on less-expensive material than gold. Yeah, the price has come down recently but it’s still very, very expensive. Maybe not for the Stanford team just making a few cells, but in terms of mass production.
“We chose gold because it was more chemically stable for our experiment,” Hagglund said. “Although the cost of the gold was virtually negligible, silver is cheaper and better from an optical point of view if you want to make a good solar cell. Our device represents an orders-of-magnitude reduction in thickness. This suggests that we can eventually reduce the thickness of solar cells.”
The Stanford research was published in the journal Nano Letters.