How Ethylene Glycol Chains Enhance the Dielectric Constant of Organic Semiconductors: Molecular Origin and Frequency Dependence

Incorporating
ethylene glycols (EGs) into organic semiconductors has become the
prominent strategy to increase their dielectric constant. However,
EG’s contribution to the dielectric constant is due to nuclear
relaxations, and therefore, its relevance for various organic electronic
applications depends on the time scale of these relaxations, which
remains unknown. In this work, by means of a new computational protocol
based on polarizable molecular dynamics simulations, the time- and
frequency-dependent dielectric constant of a representative fullerene
derivative with EG side chains is predicted, the origin of its unusually
high dielectric constant is explained, and design suggestions are
made to further increase it. Finally, a dielectric relaxation time
of ∼1 ns is extracted which suggests that EGs may be too slow
to reduce the Coulombic screening in organic photovoltaics but are
definitely fast enough for organic thermoelectrics with much lower
charge carrier velocities.