Pentacene
molecules convert a single photon into two molecular excitations
via the quantum
mechanics of singlet fission
Credit: Lawrence W
Chin, David Turban and Alex W Chin
(October 26, 2015) The
mechanism behind a process known as singlet fission, which could drive the
development of highly efficient solar cells, has been directly observed by
researchers for the first time.
An international team of scientists have observed how a
mysterious quantum phenomenon in organic molecules takes place in real time,
which could aid in the development of highly efficient solar cells.
The researchers, led by the University of Cambridge, used
ultrafast laser pulses to observe how a single particle of light, or photon,
can be converted into two energetically excited particles, known as
spin-triplet excitons, through a process called singlet fission. If singlet
fission can be controlled, it could enable solar cells to double the amount of
electrical current that can be extracted.
In conventional semiconductors such as silicon, when one
photon is absorbed it leads to the formation of one free electron that can be
harvested as electrical current. However certain materials undergo singlet
fission instead, where the absorption of a photon leads to the formation of two
spin-triplet excitons.
Working with researchers from the Netherlands, Germany and
Sweden, the Cambridge team confirmed that this ‘two-for-one’ transformation
involves an elusive intermediate state in which the two triplet excitons are ‘entangled’,
a feature of quantum theory that causes the properties of each exciton to be
intrinsically linked to that of its partner.
By shining ultrafast laser pulses – just a few
quadrillionths of a second – on a sample of pentacene, an organic material which
undergoes singlet fission, the researchers were able to directly observe this
entangled state for the first time, and showed how molecular vibrations make it
both detectable and drive its creation through quantum dynamics. The results
are reported today (26 October) in the journal Nature Chemistry.