Light-infused particles go the distance in organic semiconductors
Date:
April 29, 2022
Source:
Cornell University
Summary:
Polaritons offer the best of two very different worlds. These
hybrid particles combine light and molecules of organic material,
making them ideal vessels for energy transfer in organic
semiconductors. They are both compatible with modern electronics
but also move speedily, thanks to their photonic origins.
FULL STORY ========================================================================== Polaritons offer the best of two very different worlds. These hybrid
particles combine light and molecules of organic material, making them
ideal vessels for energy transfer in organic semiconductors. They are
both compatible with modern electronics but also move speedily, thanks
to their photonic origins.
========================================================================== However, they are difficult to control, and much of their behavior is
a mystery.
A project led by Andrew Musser, assistant professor of chemistry and
chemical biology in the College of Arts and Sciences, has found a way to
tune the speed of this energy flow. This "throttle" can move polaritons
from a near standstill to something approaching the speed of light and
increase their range -- an approach that could eventually lead to more efficient solar cells, sensors and LEDs.
The team's paper, "Tuning the Coherent Propagation of Organic Exciton- Polaritons through Dark State Delocalization," published April 27 in
Advanced Science. The lead author is Raj Pandya of the University of
Cambridge.
Over the last several years, Musser and colleagues at the University of Sheffield have explored a method of creating polaritons via tiny sandwich structures of mirrors, called microcavities, that trap light and force
it to interact with excitons -- mobile bundles of energy that consist
of a bound electron-hole pair.
They previously showed how microcavities can rescue organic semiconductors
from "dark states" in which they don't emit light, with implications
for improved organic LEDs.
==========================================================================
For the new project, the team used a series of laser pulses, which
functioned like an ultrafast video camera, to measure in real time how
the energy moved within the microcavity structures. But the team hit a speedbump of their own.
Polaritons are so complex that even interpreting such measurements can
be an arduous process.
"What we found was completely unexpected. We sat on the data for a good
two years thinking about what it all meant," said Musser, the paper's
senior author.
Eventually the researchers realized that by incorporating more mirrors
and increasing the reflectivity in the microcavity resonator, they were
able to, in effect, turbocharge the polaritons.
"The way that we were changing the speed of the motion of these particles
is still basically unprecedented in the literature," he said. "But now,
not only have we confirmed that putting materials into these structures
can make states move much faster and much further, but we have a lever to actually control how fast they go. This gives us a very clear roadmap now
for how to try to improve them." In typical organic materials, elementary excitations move on the order of 10 nanometers per nanosecond, which is
roughly equivalent to the speed of world- champion sprinter Usain Bolt, according to Musser.
==========================================================================
That may be fast for humans, he noted, but it is actually quite a slow
process on the nanoscale.
The microcavity approach, by contrast, launches polaritons a
hundred-thousand times faster -- a velocity on the order of 1% of the
speed of light. While the transport is short lived -- instead of taking
less than a nanosecond, it's less than picosecond, or about 1,000 times
briefer -- the polaritons move 50 times further.
"The absolute speed isn't necessarily important," Musser said. "What is
more useful is the distance. So if they can travel hundreds of nanometers,
when you miniaturize the device -- say, with terminals that are 10's of nanometers apart -- that means that they will go from A to B with zero
losses. And that's really what it's about." This brings physicists,
chemists and material scientists ever closer to their goal of creating
new, efficient device structures and next-generation electronics that
aren't stymied by overheating.
"A lot of technologies that use excitons rather than electrons only
operate at cryogenic temperatures," Musser said. "But with organic semiconductors, you can start to achieve a lot of interesting, exciting functionality at room temperature. So these same phenomena can feed into
new kinds of lasers, quantum simulators, or computers, even. There are a
lot of applications for these polariton particles if we can understand
them better." Co-authors include Scott Renken, MS '21 of the Musser
Group; and researchers from the University of Cambridge, the University
of Sheffield and Nanjing University.
The research was supported by the Engineering and Physical Sciences
Research Council in the United Kingdom, the University of Cambridge and
the U.S.
Department of Energy.
========================================================================== Story Source: Materials provided by Cornell_University. Original written
by David Nutt. Note: Content may be edited for style and length.
========================================================================== Journal Reference:
1. Raj Pandya, Arjun Ashoka, Kyriacos Georgiou, Jooyoung Sung, Rahul
Jayaprakash, Scott Renken, Lizhi Gai, Zhen Shen, Akshay Rao,
Andrew J.
Musser. Tuning the Coherent Propagation of Organic
Exciton‐Polaritons through Dark State Delocalization. Advanced
Science, 2022; 2105569 DOI: 10.1002/advs.202105569 ==========================================================================
Link to news story:
https://www.sciencedaily.com/releases/2022/04/220429144921.htm
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