posted on 2018-02-02, 12:52authored byBrendan
D. Folie, Jonah B. Haber, Sivan Refaely-Abramson, Jeffrey B. Neaton, Naomi S. Ginsberg
Singlet fission is
the spin-conserving process by which a singlet
exciton splits into two triplet excitons. Singlet fission occurs via
a correlated triplet pair intermediate, but direct evidence of this
state has been scant, and in films of TIPS-pentacene, a small molecule
organic semiconductor, even the rate of fission has been unclear.
We use polarization-resolved transient absorption microscopy on individual
crystalline domains of TIPS-pentacene to establish the fission rate
and demonstrate that the initially created triplets remain bound for
a surprisingly long time, hundreds of picoseconds, before separating.
Furthermore, using a broadband probe, we show that it is possible
to determine absorbance spectra of individual excited species in a
crystalline solid. We find that triplet interactions perturb the absorbance,
and provide evidence that triplet interaction and binding could be
caused by the π-stacked geometry. Elucidating the relationship
between the lattice structure and the electronic structure and dynamics
has important implications for the creation of photovoltaic devices
that aim to boost efficiency via singlet fission.