Energy

Film captures wasted wavelengths of light to boost solar cell efficiency

Film captures wasted wavelengths of light to boost solar cell efficiency
A new thin film captures blue photons from sunlight and converts them into red ones that silicon solar cells can use to produce electricity
A new thin film captures blue photons from sunlight and converts them into red ones that silicon solar cells can use to produce electricity
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A new thin film captures blue photons from sunlight and converts them into red ones that silicon solar cells can use to produce electricity
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A new thin film captures blue photons from sunlight and converts them into red ones that silicon solar cells can use to produce electricity

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.

Source: NYU Tandon

5 comments
5 comments
Malcolm Jacks
Great stuff, I have sola panels on my roof in the UK for about 9 years now, I hope this process will allow it to be added to existing sola panels.
Karmudjun
Excellent synopsis Michael. I knew perovskite based solar cells were improving but had unique environmental issues all its own. It sounds like this thin film product will yield a percentage of the benefit a perovskite PV cell without adding so much to the recycling process and waste stream. It makes sense that this is geared to new installations, but when will these films be commercial? What a boon this would be for older installations 'losing efficiency' while missing the wavelengths that silicon solar was never geared for. How much of a boost could a retrofit provide if it is even possible?
noteugene
Doesn't state how much of a boost this technology can provide. Seems that you could have been enabled to have stated that. Or what efficiency rating you can now achieve..
TechGazer
The announcement is missing something obvious: a comparison of real-life solar efficiency between a coated cell and an uncoated one. That would have been simple to do, resulting in something like: "Uncoated efficiency: 23.5%. Coated efficiency: 31.2%" The lack suggests that the real-life improvement isn't all that much.

Another missing piece: of the photons re-emitted, what percentage actually gets absorbed by the silicon? What percentage simply leave the panel? I suppose there will be further refinements to improve that. Can't simply use an IR reflective material, since that would block the incoming IR.

Yet another lack: lifespan. Perovskite cells are still quite short-lived. How long will this film last? If it's much less than the silicon's lifespan, then it sure would be nice if they could make this a coating that can be sprayed on 'in the field' and easily removed 'in the field' for another recoating.

Still, all improvements have potential. I'm happy with my solar panel, which is providing the power that's running this off-grid computer.
paul314
One red photon out for each blue photon in isn't really 100%, because an (infra)red photon carries less than half as much energy as a blue/ultraviolet photon. There are processes where you can get multiple photons out that carry (almost) all the energy of each incoming one, but doing even in a lab usually requires some additional source of energy.