New silicon device converts blue photons into red photons

Researchers have developed a new hybrid device -- pairing silicon with organic, carbon-based molecules -- that can convert blue photons into red photons, paving the way for more efficient solar energy conversion.

Silicon's electronic properties make it a popular choice for a variety of technologies. The material, one of Earth's most abundant, is used to make everything from semiconductors to solar cells. But silicon isn't great at turning light into electricity.

While silicon can convert red photons into electricity just fine, its attempts to convert blue photons, which carry twice as much energy as red photons, yields mostly wasted thermal energy.

For the new device, engineers paired silicon with a carbon-based material called anthracene that converts blue photons into red photons, which the silicon can more easily convert into electricity.

The device can work in reverse, too, which could prove useful to medical imaging and quantum technologies.

"The organic molecule we've paired silicon with is a type of carbon ash called anthracene. It's basically soot," lead researcher Sean Roberts, an assistant professor of chemistry at the University of Texas, said in a news release. "We now can finely tune this material to react to different wavelengths of light. Imagine, for quantum computing, being able to tweak and optimize a material to turn one blue photon into two red photons or two red photons into one blue. It's perfect for information storage."

Scientists have long considered the possibility of pairing silicon with organic, carbon-based molecules, but attempts to layer the two materials failed to yield the "spin-triplet exciton transfer" needed to convert blue and green light into red.

For the new device, described this week in the journal Science Advances, researchers used tiny chemical wires to link silicon nanocrystals and anthracene molecules, enabling the novel form of energy transfer.

"The challenge has been getting pairs of excited electrons out of these organic materials and into silicon. It can't be done just by depositing one on top of the other," Roberts said. "It takes building a new type of chemical interface between the silicon and this material to allow them to electronically communicate."

Scientists studied the efficacy of their new wire links using laser imaging. The observations showed the interface enables 90 percent of the energy to move between the silicon nanocrystals and anthracene molecules.

Researchers suggest the breakthrough could enable the production of miniature electronics, as well as enable applications in medicine, bioimaging and solar cell technologies.

"The novelty is really how to get the two parts of this structure -- the organic molecules and the quantum confined silicon nanocrystals -- to work together," said Lorenzo Mangolini, an associate professor of mechanical engineering at the University of California, Riverside. "We are the first group to really put the two together."

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