Unified Description of Charge-Carrier Mobilities in Disordered Semiconducting Polymers

Abstract

From a numerical solution of the master equation for hopping transport in a disordered energy landscape with a Gaussian density of states, we determine the dependence of the charge-carrier mobility on temperature, carrier density, and electric field. Experimental current-voltage characteristics in devices based on semiconducting polymers are excellently reproduced with this unified description of the mobility. At room temperature it is mainly the dependence on carrier density that plays an important role, whereas at low temperatures and high fields the electric field dependence becomes important. Omission in the past of the carrier-density dependence has led to an underestimation of the hopping distance and the width of the density of states in these polymers.

Origin of reduced polaron recombination in organic semiconductor devices

“…For coarser phase separations, the situation becomes more difficult, as band bending between the two phases cannot be described with the effective medium. Nevertheless, as parameters derived from microscopic Monte Carlo and Master equation simulations 23 and analytic theory 26,27 can be used to describe the properties of the donor-acceptor blend, the use of macrosopic simulations offers a very good insight into the impact of microscopic charge transport and recombination properties on the macroscopic device parameters such as current-voltage characteristics. Indeed, macroscopic simulations complement the microscopic point of view very well, in particular as also asymmetries due to different work functions for electron and hole injection, and their influence on the device properties can be studied.…”

Universality of AC conductivity: Random site-energy model with Fermi statistics

“…For the situation of a Gaussian DOS we recently calculated the DC charge-carrier mobility as a function of charge-carrier density with the same master equation. 39 More recently, we considered the validity of the mean-field approximation in this context by taking into account the correlations between nearestneighbor pairs. 40 We found that these correlations suppress the mean-field mobility by only a few percent, even at charge-carrier concentrations of 0.5 per site, which is the situation considered here.…”

Diffusion-enhanced hole transport in thin polymer light-emitting diodes

“…Such a transport model has recently been developed. 8 In the classical model for SCL conduction, there are two important requisites: The first is the presence of an Ohmic contact, such that the electric field at the injecting contact is close to zero. Furthermore, the amount of injected charges scales linearly with the applied voltage.…”

“…In order to fit the J-V at higher voltages, a density and field dependent mobility has been taken into account. 8 For the device with a thickness of 318 nm, a low-density mobility h ͑0,T͒ ͓Eq. ͑1͔͒ was found to be 3.0 ϫ 10 −11 m 2 / V s at room temperature, which is in agreement with earlier reported values.…”