Nanophotonics team creates low-voltage, multicolor, electrochromic glass 8 March 2017

to different types of color depending on how we apply a very low voltage."

Adam Lauchner, an applied physics graduate student at Rice and co-lead author of the study, said LANP's color-changing glass has polarity- dependent colors, which means that a positive voltage produces one color and a negative voltage produces a different color.

"That's pretty novel," Lauchner said. "Most color- changing glass has just one color, and the multicolor varieties we're aware of require significant voltage." Adding and removing an electron from neutral perylene (center column) produces an anion (left) and cation Glass that changes color with an applied voltage is (right), respectively, with different electronic structures known as "electrochromic," and there's a growing (middle row). Upon excitation with visible light, the anion demand for the light- and heat-blocking properties and cation give rise to two unique molecular of such glass. The projected annual market for resonances, each with their own distinct color (bottom electrochromic glass in 2020 has been estimated at row). Credit: Grant Stec/ more $2.5 billion.

Lauchner said the glass project took almost two years to complete, and he credited co-lead author Rice University's latest research Grant Stec, a Rice undergraduate researcher, with could expand the color palette for companies in the designing the perylene-containing nonwater-based fast-growing market for glass windows that change conductive gel that's sandwiched between glass color at the flick of an electric switch. layers. In a new paper in the American Chemical Society "Perylene is part of a family of molecules known as journal ACS Nano, researchers from the laboratory polycyclic aromatic hydrocarbons," Stec said. of Rice pioneer Naomi Halas report "They're a fairly common byproduct of the using a readily available, inexpensive hydrocarbon petrochemical industry, and for the most part they molecule called perylene to create glass that can are low-value byproducts, which means they're turn two different colors at low voltages. inexpensive." "When we put charges on the molecules or remove There are dozens of polycyclic aromatic charges from them, they go from clear to a vivid hydrocarbons (PAHs), but each contains rings of color," said Halas, director of the Laboratory for carbon atoms that are decorated with hydrogen Nanophotonics (LANP), lead scientist on the new atoms. In many PAHs, carbon rings have six sides, study and the director of Rice's Smalley-Curl just like the rings in graphene, the much-celebrated Institute. "We sandwiched these molecules subject of the 2010 Nobel Prize in physics. between glass, and we're able to make something that looks like a window, but the window changes

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Grant Stec and Adam Lauchner of Rice University’s Laboratory for Nanophotonics have used an inexpensive Rice University researchers demonstrated a new type of hydrocarbon molecule called perylene to create a low- glass that turns from clear to black when a low voltage is voltage, multicolor, electrochromic glass. Credit: Jeff applied. The glass uses a combination of molecules that Fitlow/Rice University block almost all visible light when they each gain a single electron. Credit: Jeff Fitlow/Rice University

"This is a really cool application of what started as fundamental science in plasmonics," Lauchner She noted that large sheets of atomically thin said. graphene have been found to support , but they emit infrared light that's invisible to the A plasmon is wave of energy, a rhythmic sloshing human eye. in the sea of electrons that constantly flow across the surface of conductive . Depending "Studies have shown that if you make graphene upon the frequency of a plasmon's sloshing, it can smaller and smaller, as you go down to interact with and harvest the energy from passing nanoribbons, nanodots and these little things called light. In dozens of studies over the past two nanoislands, you can actually get graphene's decades, Halas, Rice physicist Peter Nordlander plasmon closer and closer to the edge of the visible and colleagues have explored both the basic regime," Lauchner said. physics of plasmons and potential applications as diverse as cancer treatment, solar-energy In 2013, then-Rice physicist Alejandro Manjavacas, collection, electronic displays and optical a postdoctoral researcher in Nordlander's lab, computing. showed that the smallest versions of graphene—PAHs with just a few carbon The quintessential plasmonic is rings—should produce visible plasmons. Moreover, metallic, often made of gold or silver, and precisely Manjavacas calculated the exact colors that would shaped. For example, gold , which Halas be emitted by different types of PAHs. invented at Rice in the 1990s, consist of a nonconducting core that's covered by a thin shell of "One of the most interesting things was that unlike gold. plasmons in metals, the plasmons in these PAH molecules were very sensitive to charge, which "Our group studies many kinds of metallic suggested that a very small electrical charge would nanoparticles, but graphene is also conductive, and produce dramatic colors," Halas said. we've explored its plasmonic properties for several years," Halas said.

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Provided by Rice University

Student researchers Grant Stec (left) and Adam Lauchner (right) with Rice plasmonics pioneer Naomi Halas, director of Rice University’s Laboratory for Nanophotonics. Credit: Jeff Fitlow/Rice University

Lauchner said the project really took off after Stec joined the research team in 2015 and created a perylene formulation that could be sandwiched between sheets of conductive glass.

In their experiments, the researchers found that applying just 4 volts was enough to turn the clear window greenish-yellow and applying negative 3.5 volts turned it blue. It took several minutes for the windows to fully change color, but Halas said the transition time could easily be improved with additional engineering.

Stec said the team's other window, which turns from clear to black, was produced later in the project.

"Dr. Halas learned that one of the major hurdles in the electrochromic device industry was making a window that could be clear in one state and completely black in another," Stec said. "We set out to do that and found a combination of PAHs that captured no visible light at zero volts and almost all visible light at low voltage."

More information: Grant J. Stec et al. Multicolor Electrochromic Devices Based on Molecular Plasmonics, ACS Nano (2017). DOI: 10.1021/acsnano.7b00364

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APA citation: Nanophotonics team creates low-voltage, multicolor, electrochromic glass (2017, March 8) retrieved 28 September 2021 from https://phys.org/news/2017-03-nanophotonics-team-low-voltage- multicolor-electrochromic.html

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