Researchers develop new
design rule for generating excitons will help advance next-generation devices
Columbia University – August 19, 2019 --Researchers
at Columbia University have developed a way to harness more power from singlet
fission to increase the efficiency of solar cells, providing a tool to help
push forward the development of next-generation devices.
In a study published this month in Nature
Chemistry, the team details the design of organic molecules that are
capable of generating two excitons per photon of light, a process called
singlet fission. The excitons are produced rapidly and can live for much longer
than those generated from their inorganic counterparts, which leads to an
amplification of electricity generated per photon that is absorbed by a solar
cell.
"We have developed a new design
rule for singlet fission materials," said Luis Campos, an associate
professor of chemistry and one of three principal investigators on the study.
"This has led us to develop the most efficient and technologically useful
intramolecular singlet fission materials to date. These improvements will open
the door for more efficient solar cells."
All modern solar panels operate by the
same process -- one photon of light generates one exciton, Campos explained.
The exciton can then be converted into electric current. However, there are
some molecules that can be implemented in solar cells that have the ability to
generate two excitons from a single photon -- a process called singlet fission.
These solar cells form the basis for next-generation devices, which are still
at infancy. One of the biggest challenges of working with such molecules,
though, is that the two excitons "live" for very short periods of
time (tens of nanoseconds), making it difficult to harvest them as a form of
electricity.
In the current study, funded in part by
the Office of Naval Research, Campos and colleagues designed organic molecules
that can quickly generate two excitons that live much longer than the
state-of-the-art systems. It is an advancement that can not only be used in
next-generation solar energy production, but also in photocatalytic processes
in chemistry, sensors, and imaging, Campos explained, as these excitons can be
used to initiate chemical reactions, which can then be used by industry to make
drugs, plastics, and many other types of consumer chemicals.
"Intramolecular singlet fission has
been demonstrated by our group and others, but the resulting excitons were
either generated very slowly, or they wouldn't last very long," Campos
said. "This work is the first to show that singlet fission can rapidly
generate two excitons that can live for a very long time. This opens the door
to fundamentally study how these excitons behave as they sit on individual
molecules, and also to understand how they can be efficiently put to work in
devices that benefit from light-amplified signals."
The team's design strategy should also
prove useful in separate areas of scientific study and have many other
yet-unimaginable applications, he added.
Campos' study co-authors are: Samuel
Sanders and Andrew Pun, of Columbia University; Matthew Y. Sfeir, of City
University of New York; and Amir Asadpoordarvish, of the University of New
South Wales.
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