Atomistic Simulation of Phase Transitions and Charge Mobility for the Organic Semiconductor Ph-BTBT-C10

We
present a computational study of the molecular organization
and charge mobility of Ph-BTBT-C10, a high performance organic semiconductor
of considerable current interest. We have observed for the first time
by atomistic molecular dynamics the formation of an ordered smectic
phase on cooling down from the isotropic melt and upon heating the
crystal, for this system, in good agreement with experiment. Although
we could observe only a smectic A and not a smectic E phase, the temperature
variation of the hole mobility estimated from hopping model calculations
reproduces the main features of experiments. The crystal phase is
characterized by high mobility bilayers defined by the aromatic π-conjugated
cores, but it is effectively insulating in the orthogonal direction.
The smectic phase is characterized by more disordered monolayers,
which have a good in-plane mobility and a lower, but still appreciable,
degree of charge transport across the layers. This feature may be
advantageous for applications requiring materials with evenly balanced,
three-dimensional conduction paths.