Strategies for Enhancing the Dielectric Constant of Organic Materials

High dielectric constant organic semiconductors, often
obtained
by the use of ethylene glycol (EG) side chains, have gained attention
in recent years in the efforts of improving the device performance
for various applications. Dielectric constant enhancements due to
EGs have been demonstrated extensively, but various effects, such
as the choice of the particular molecule and the frequency and temperature
regime, that determine the extent of this enhancement require further
understanding. In this work, we study these effects by means of polarizable
molecular dynamics simulations on a carefully selected set of fullerene
derivatives with EG side chains. The selection allows studying the
dielectric response in terms of both the number and length of EG chains
and also the choice of the group connecting the fullerene to the EG
chain. The computed time- and frequency-dependent dielectric responses
reveal that the experimentally observed rise of the dielectric constant
within the kilo/megahertz regime for some molecules is likely due
to the highly stretched dielectric response of the EGs: the initial
sharp increase over the first few nanoseconds is followed by a smaller
but persistent increase in the range of microseconds. Additionally,
our computational protocol allows the separation of different factors
that contribute to the overall dielectric constant, providing insights
to make several molecular design guides for future organic materials
in order to enhance their dielectric constant further.