Scientists Discover a Material That Can Recycle Sunlight

March 30, 2016 | Joanne Kennell

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We may be on the verge of a solar power revolution.

A new study, published in the journal Science, has made an exciting new discovery about a group of materials already making waves in solar cell technology: hybrid lead halide perovskites.

Amazingly, the researchers demonstrated that these types of solar cells can not only be produced cheaply and with easily synthesized materials — making solar power much more commercially viable — but they also create some light energy of their own.

“We already knew that these materials were good at absorbing light and producing charge-carriers,” said co-author Dr. Felix Deschler of Cambridge University, UK, in a telephone interview with The Christian Science Monitor (CSM). “But now we have demonstrated that they can also recombine to produce photons again.”

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Solar cells work by absorbing light energy from the sun, converting this energy into an electrical charge, and then transferring that charge to electrodes which transport the energy out for the world to use.

Hybrid lead halide perovskites were already known to do this efficiently. However, Deschler and his team were able to show that the perovskites can do so much more: they are able to emit light themselves after creating an electric charge and then reabsorb that light energy.

It is a solar cell that actually acts like a concentrator — which means it’s able to produce more energy and boost the voltage obtained from a given amount of light. Currently, no other solar cell materials have this recycling ability.

“Why this is now a big thing is because the current record of photo cell efficiency rests at 20-21 percent, whereas the absolute limit is 33 percent,” said Deschler to CSM. “Our results suggest a route to achieve that limit.”

Solar cell efficiency refers to the percentage of energy, given a certain amount of light, that the cells harness for use. According to a 1961 paper by William Shockley and Hans Queisser, theoretical thermodynamics caps solar efficiency at 33 percent. Deschler's recent work points to not only climbing closer to that ceiling, but using cheaper materials to do so.

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“You wouldn’t expect photon recycling in our materials because their fabrication is so much simpler than others,” Deschler explained to CSM. “Our materials are very cheap to make, very versatile.”

However, there is some skepticism regarding how these materials are made. Since they are made in a solution, there is little control over how the structures form. For example, if there are impurities in the structure, you are left with a “defect site,” which makes the material “messier” in terms of light absorption. Without these impurities, there is what is known as a “sharp absorption onset,” allowing efficient absorption of light.

“So, while they are very efficient,” said Deschler to CSM, “we’re still trying to understand why and how they’re better than other materials.”

As expected, the results have gained a lot of interest from other solar cell producers who are looking for a cheaper and more efficient way to harness the power of the sun.

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