Polaron effects and electric field dependence of the charge carrier mobility in conjugated polymers

Abstract

Charge transport in conjugated polymers has been investigated using Monte Carlo simulations implemented on top of the Marcus theory for donor-acceptor transition rates. In particular, polaron effects and the dependency of the mobility on the temperature and the applied electric field have been studied. The conclusions are that while the qualitative temperature dependence is similar to that predicted by Miller-Abrahams theory in the Gaussian disorder model (GDM), the electric field dependence is characterized by a crossover into the Marcus inverted region, not present in the GDM. Furthermore, available analytical approximations to describe the electric field dependence of the mobility in Marcus theory fail to fit the simulation data and hence cannot be used to directly draw conclusions about the importance of polaron effects for charge transport in conjugated polymers.

Understanding hopping transport and thermoelectric properties of conducting polymers

“…This section describes the main steps in the simulation of the hopping transport based on the kinetic Monte Carlo method [25,26,51]. The method includes a definition of a lattice, assigning energy levels to every site according to the chosen DOS, and then running the simulation by monitoring a random walk of charge carriers between the sites.…”

Polaron effect and energetic disorder dependence of Seebeck coefficient in organic transistors

“…What is more, the effect of polaron effects on Seebeck coefficient in organic transistors is also ambiguous. Since the carrier transport in organic semiconductor can be greatly affected by the formation of polarons [13,16,17], it should be included to describe the charge carrier thermoelectric transport characteristics in organic transistors.…”

Monte Carlo simulations of charge transport in organic systems with true off-diagonal disorder

“…(2) to account for the number of monomer units included in the transport molecules in the case of PPV chromophores. 25 In this case, the exponential prefactor is given by…”

“…This part of the charge transport is not included when calculating the mobility, i.e., the charge carriers are allowed to relax before their velocity is measured in steady state. 25 The procedure described above is repeated a large number of times until the statistical fluctuations are negligible. Furthermore, the simulations were run on sixteen different snapshots extracted from the last nanosecond of the MD trajectories.…”

“…25 The mobility measured is taken from the steady state velocity of the charge carriers moving in the systems described above. To be able to reach a steady state transport, the systems are made infinite by imposing periodic boundary conditions.…”