The Multiplicity of π–π Interactions of Fused-Ring Electron Acceptor Polymorphs on the Exciton Migration and Charge Transport

Efficient long-range exciton migration and charge transport
are
the key parameters for organic photovoltaic materials, which strongly
depend on the molecular stacking modes. Herein, we extracted the stacked
structures of the archetype fused-ring electron acceptor molecule,
ITIC, based on the information on four polymorphic crystals and investigated
the relationship between molecular stacking modes and exciton migration/charge
transport properties through the intermolecular Coulomb coupling and
charge transfer integral calculation. Experimentally, the thin film
texture is crystallized through a post-annealing treatment through
grazing-incidence wide-angle X-ray scattering (GIWAXS) measurements,
which lead to the enhanced exciton migration through exciton–exciton
annihilation in the femtosecond transient absorption (fs-TA) measurements.
This work demonstrates the relationship between the molecular arrangement
and the exciton migration and electron transport and highlights the
significance of optimizing molecular stacking for the development
of high-performance electron acceptor materials.