Film captures wasted wavelengths of light to boost solar cell efficiency

2022-07-19

Solar cells are one of the most important technologies in the transition to renewable energy, but there’s still plenty of room for improvement. Researchers at New York University (NYU) Tandon have now developed a thin film that boosts solar cell efficiency by converting wasted wavelengths of light into ones that can be used to produce electricity.

Silicon is the material of choice for most solar cells in use today, but while it excels at absorbing the red end of the visible spectrum of sunlight, it all but ignores shorter wavelengths like ultraviolet and blue light. Scientists have been experimenting with different solar cell designs, materials and dyes that might be able to make use of more of the spectrum, but so far it’s been tricky to make meaningful headway.

Now, the NYU Tandon researchers may have made a breakthrough, with a thin film that can convert UV and blue photons from sunlight into near-infrared photons. The film could be used to boost the efficiency of an existing silicon solar cell by essentially allowing it to harvest energy that would otherwise go to waste.

Importantly, it doesn’t block the other wavelengths of light that silicon can readily tap into. And as an added bonus, reducing the amount of UV radiation that hits the solar cell can help them last longer.

The film is made up of an inorganic perovskite material doped with small amounts of ytterbium. The perovskite is adept at absorbing blue light and transferring that energy to the ytterbium, which emits it as near-infrared light. These red photons can then be picked up by the silicon solar cell, supplementing its usual diet coming directly from the Sun.

In tests, the team found that the film could convert blue photons to red with an efficiency of 82.5 percent. It’s important not to get this figure confused with the efficiency of the solar cell itself – those are still hovering in the mid-20s for silicon – but this new film should help boost that. To what extent is a question for further tests to address.

The researchers have already experimented with ways to improve their design. In a follow-up study, they changed the temperature of the production process to reduce the amount of bismuth that escapes the material. The resulting films boasted blue to red photon conversion efficiencies as high as 95 percent.

And there might still be room to go higher. The team says it could be possible to break the 100-percent efficiency barrier, which would mean that more red photons are being emitted than the number of blue photons striking the film. The path to that potential breakthrough remains murky for now though.

“We do not exactly know yet (how to boost efficiency over 100 percent),” Eray Aydil, lead author of the study, told New Atlas. “However, we have some ideas based on the hypothesis of how emission happens in the first place. We are taking two routes – (1) conducting experiments to find out about the details of what makes this material special, and (2) we are exploring similarly structured materials with different elemental substitutions.”

The research was published in the journal Materials Horizons.

New Atlas, 19 July 2022
; https://newatlas.com