What’s not to love about solar energy? Using photovoltaic cells — tiny semiconductors that convert light directly into electricity — we’re able to harness the power of the Sun itself, turning it into wattage to power our homes.
It’s great in theory, but there’s a huge catch. Of all the power our star graciously beams to us, only about 33 percent of it can ever be turned into usable electricity, and most commercial solar panels don’t even come close to that.
This ceiling is known as the Shockley-Queisser limit, named after the two physicists who first theorized it back in 1961. The reason comes down to thermodynamics: sunlight comes to us as a vast rainbow of light energy, but we can only convert a narrow slice of that spectrum into usable electricity. The rest either passes through, or is lost as excess heat.
But now it’s possible that a novel process could blow the Shockley-Quiesser limit wide open. In a new paper published in the Journal of the American Chemical Society, a team of scientists in Japan and Germany detail a method they say can capture the parts of the light spectrum that would otherwise be burned off as residual heat.
Basically, the researchers found that if you blast a certain compound with high-energy blue light — a part of the light band that we normally can’t convert to electricity — you can split the incoming energy into two usable parts. Using their method, the team was able to achieve around 130 percent energy conversion efficiency, meaning that for every 100 photons that entered, they could harvest 130 usable energy carriers.
To achieve the breakthrough, the team mixed the organic molecule tetracene with the metallic element molybdenum. While scientists had previously used tetracene to harness this kind of high-energy blue light before, there were practical issues preventing prolonged energy conversion, which they say the addition of molybdenum solved.
“We have two main strategies to break through this [Shockley-Queisser] limit,” Yoichi Sasaki, a chemist at Kyushu University and one of the study’s coauthors, said in a press release. “One is to convert lower-energy infrared photons into higher-energy visible photons. The other, what we explore here, is to use singlet fission to generate two excitons from a single exciton photon.”
It’s important to highlight that these are controlled lab tests so far. The most efficient commercially available solar panels still ring in with around a 25 percent efficiency rate, and that probably won’t change anytime soon. Still, it’s the biggest crack so far in a theoretical ceiling that’s stood for over 60 years.
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