Researchers reshape solar spectrum to turn more light to electricity

Researchers have developed a technique for capturing photons that normally bypass photovoltaic cells inside solar panels. The technology promises to boost solar cell efficiency.

Currently, solar cells aren't capable of absorbing photons in the visible and near-infrared regions of the solar spectrum. But researchers at the University of California, Riverside created a new filter made of a unique hybrid material that captures, converts and combines these elusive photons into higher-energy spectral bands.

"The infrared region of the solar spectrum passes right through the photovoltaic materials that make up today's solar cells," Christopher Bardeen, a professor of chemistry at Riverside, explained in a press release.

"This is energy lost, no matter how good your solar cell," added Ming Lee Tang, an assistant professor of chemistry. "The hybrid material we have come up with first captures two infrared photons that would normally pass right through a solar cell without being converted to electricity, then adds their energies together to make one higher energy photon."

The "upconverted" photon is absorbed by the photovoltaic materials inside today's solar panels. Researchers say they are, in effect, "reshaping the solar spectrum."

The researchers' hybrid material is a combination of inorganic and organic materials. A inorganic mix of cadmium selenide and lead selenide semiconductor nanocrystals work to absorb and convert visible light to near-infrared and vice versa, while an organic compound coating serves to combine the converted photons.

"Put simply, the inorganics in the composite material take light in; the organics get light out," Bardeen explained.

Bardeen says their research -- which was published this week in the journal Nano Letters -- could have applications outside of the solar energy industry.

"The ability to move light energy from one wavelength to another, more useful region, for example, from red to blue, can impact any technology that involves photons as inputs or outputs."