  Carrier multiplication by singlet exciton fission enhances photovoltaic
conversion efficiencies in organic solids. This decay of one singlet exciton
into two triplet states promises to overcome the Shockley-Queisser limit as up
to two electrons may be harvested per absorbed photon. Intermolecular coupling
is deemed mandatory for both, singlet exciton fission and a band-like
transport. Such a coupling is manifested, $e.g.$, by the Davydov-splitting of
the lowest-energy exciton transition in crystalline organic solids. For the
model system perfluoropentacene, the corresponding transitions in the
experimental, polarisation-resolved absorption spectra are identified by
theoretical calculations based on the concept of H- and J- aggregation. Optical
injection into the first vibronic progression of the fundamental exciton
transitions significantly perturbs the higher-energy transitions that are
associated to H-type aggregates of the $S_0 \rightarrow S_3$ transition during
and following efficient singlet exciton fission. These findings underline the
necessity for efficient carrier extraction as triplet accumulation may be
detrimental to both, singlet exciton fission and any potentially band like
transport. More generally, our observations indicate that electronic
excitations can perturb the electronic band structure in organic crystals and
highlight their correlated nature by potentially distorting the lattice.
