Solar Cell Materials Adapted for Nanowire Lasers
BERKELEY, Calif., March 2, 2016 — Next-generation solar cell material have been adapted into 200-nm nanowire lasers that produce bright, stable laser light, which could enable optoelectronic devices.
Standard techniques that produce nanowires can require expensive equipment and exotic conditions, such as high temperatures, and can suffer from other shortcomings, such as limited tunability, low brightness or costly manufacturing processes, said researchers from the University of California and the Department of Energy’s Lawrence Berkeley National Laboratory.
A nanowire, composed of cesium, lead and bromide (CsPbBr3), emits bright laser light after hit by a pulse from another laser source. The nanowire laser proved to be very stable, emitting laser light for over an hour. It also was demonstrated to be broadly tunable across green and blue wavelengths. The white line is a scale bar that measures 2 μm. Courtesy of Sam Eaton/UC Berkeley.
"The whole purpose of developing nanozsized lasers is to interface photonic (light-based) devices with electronic devices seamlessly at scales relevant to today's computer chips,” said Berkeley Lab chemist Peidong Yang. “Today, these photonic devices can be bulky."
Yang's research team pioneered the development of nanowire lasers almost 15 years ago using a different blend of materials, including zinc oxide (ZnO) and gallium nitride (GaN).
In the recent work, the research team produced nanowires by dipping a thin lead-containing film into a methanol solution containing cesium, bromine and chlorine (CsPbBr3) heated to about 122 °F. A mix of cesium lead bromide crystalline structures formed, including nanowires with a diameter from 0.2 to 2.3 μm and a length ranging from 2 to 40 μm.
This scanning electron microscope image shows a collection of cesium lead bromide (CsPgbBr3)
nanowires and nanoplates grown from a chemical-dipping process. To
produce these structures, researchers dipped a thin lead-containing film
into a methanol solution containing cesium, bromine and chlorine heated
to about 122 °F. The white scale bar at the lower right represents 10
μm. The image at the bottom left shows the well-formed rectangular
end of a nanowire-the white scale bar associated with it represents 500
nm. Courtesy of Sam Eaton/UC Berkeley.
The same chemical blend, with a molecular architecture composed of cube-like crystal structures, has also proven effective in an emerging wave of new designs for high-efficiency solar cells. The resulting nanowires had a crystal structure resembling that of perovskite or salt, the researchers said, which makes them susceptible to damage from moisture in the air.
"That is one weakness — something we have to study and understand how to improve," Yang said. It may be possible to coat the nanowires with polymers or other material to make them more damage-resistant. There are also opportunities to test out other materials and learn whether they improve performance, he said, such as substituting tin for lead.
Select nanowires used in the experiment were placed on a quartz base and excited by another laser source that caused them to emit light. Researchers found that the nanowire lasers emitted light for over 1 billion cycles after being hit by an ultrafast pulse of visible, violet light that lasted just hundredths of quadrillionths of seconds, which Yang said demonstrated remarkable stability.
The researchers said these nanowires may be the first to emit laser light using a totally inorganic blend of materials, and demonstrated that the nanowire lasers could be tuned to a range of light including visible green and blue wavelengths.
"The results indicate significant promise for perovskite nanomaterials in lasing,” said Ted Sargent, a nanotechnology researcher and professor at University of Toronto who is familiar with the study. The stability of the nanolasers, which were shown to operate in air for more than an hour, was particularly impressive, he said.
The research was published in Proceedings of the National Academy of Sciences (doi: 10.1073/pnas.1600789113).
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