New Solar Cell Material Acts as a Laser As Well

The hottest new material in solar cell research has another trick up its sleeve. At the Materials Research Society meeting here, two groups reported yesterday that these new electricity-generating materials can produce laser light. Because the materials—called perovskites—are cheap and…

The hottest new material in solar cell research has another trick up its sleeve. At the Materials Research Society meeting here, two groups reported yesterday that these new electricity-generating materials can produce laser light. Because the materials—called perovskites—are cheap and easy to produce, they could help engineers create a wide variety of cheap lasers that shine a variety of colors for use in speeding data flows in the telecommunications industry.

Lasers have long been at the heart of modern telecommunications because their intense light beams can be chopped up to represent digital currency’s 1s and 0s and can travel through optical cables at light speed. But making new lasers can be a bear. Researchers must find materials that, when fed electrons, will generate light at a single wavelength. That usually requires growing materials with near-perfect crystalline quality, as defects usually gobble up the electrical charges, the photons of light, or both. Growing such high-quality materials normally requires using high temperatures, expensive equipment, and other costly steps. Making the best solar cell materials requires similarly expensive setups. Perovskites have burst onto the solar scene over the last couple of years because it turns out they form near-perfect complex crystalline structures by simply depositing them from ready-made solutions at low temperatures. But were they good enough to make lasers, an even more demanding application?

At the meeting, two groups reported that, in fact, they are. The first, led by Edward Sargent, an electrical engineer at the University of Toronto in Canada, started by simply blasting a perovskite film with a beam of ultraviolet light. The scientists found that light reemerged from the film at a tight range of frequencies in the infrared portion of the spectrum. That was a hint that perovskites could make a good laser material. But it wasn’t a laser yet. To make a laser, researchers must create a structure that bounces light back and forth. In the right material, that shuttling light stimulates a cascade of additional photons to emerge all at a single frequency. So Sargent and his colleagues crafted their perovskites into spheres that prompt light to bounce around inside and found that it emerged as infrared laser light. Meanwhile, Henry Snaith, a physicist at the University of Oxford in the United Kingdom, reported that when his team sandwiched a perovskite film in between laser mirrors known as Bragg reflectors, it, too, produced infrared laser light when first hit with laser light of a shorter wavelength.
Perovskites still have a long way to go before they’ll make commercially viable lasers, Sargent says. For starters, researchers must show that the materials can lase when plugged into an electrical outlet, rather than when hit with another beam of laser light. Neither Sargent’s group nor Snaith’s has done that yet. If they can, Sargent says, “it would be very important” because perovskites could be grown on cheap silicon wafers, thus potentially creating a new class of cheap lasers for the telecommunications industry.
Even without that step, the new work underscores just how impressive perovskites are for something so simple and cheap to grow, says David Ginley, a materials scientist at the National Renewable Energy Laboratory in Golden, Colorado. “It’s really remarkable how good the material is.”

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