Polymorphism
of Crystalline Molecular Donors for Solution-Processed
Organic Photovoltaics
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Abstract
Using
ab initio calculations and classical molecular dynamics simulations
coupled to complementary experimental characterization, four molecular
semiconductors were investigated in vacuum, solution, and crystalline
form. Independently, the molecules can be described as nearly isostructural,
yet in crystalline form, two distinct crystal systems are observed
with characteristic molecular geometries. The minor structural variations
provide a platform to investigate the subtlety of simple substitutions,
with particular focus on polymorphism and rotational isomerism. Resolved
crystal structures offer an exact description of intermolecular ordering
in the solid state. This enables evaluation of molecular binding energy
in various crystallographic configurations to fully rationalize observed
crystal packing on a basis of first-principle calculations of intermolecular
interactions