Abstract
We investigate the transport properties of charge carriers in disordered organic semiconductors using a model that relates a mobility with charge carriers (not with small polarons) hopping by thermal activation. Considering Miller and Abrahams expression for a hopping rate of a charge carrier between localized states of a Gaussian distributed energies, we employ Monte Carlo simulation methods, and calculate the average mobility of finite charge carriers focusing on a lower density region where the mobility was shown experimentally to be independent of the density. There are Monte Carlo simulation results for density dependence of mobility reported for hopping on regularly spaced states neglecting the role of spatial disorder, which does not fully mimic the hopping of charge carriers on randomly distributed states in disordered system as shown in recent publications. In this work we include the spatial disorder and distinguish the effects of electric field and density which are not separable in the experiment, and investigate the influence of density and electric field on mobility at different temperatures comparing with experimental results and that found in the absence of the spatial disorder. Moreover, we analyze the role of density and localization length on temperature and electric field dependence of mobility. Our results also give additional insight regarding the value of localization length that has been widely used as 0.1b where b is a lattice sites spacing.
Highlights
Organic polymers that show semiconducting properties because of the weak πbonding along the polymer chain have received widespread attention in the scientific community due to their easy manufacturing and possible applications in modern electronic devices: Organic light-emitting diodes (OLEDs) [1], organic field effect transistors (OFETs) [2,3,4], and organic solar cells [5]
The results found show that the hole mobility of the film used in polymer FETs (PFETs) was larger than that used in polymer LEDs (PLEDs) by 3 orders of magnitude
We have studied and presented a generalized view on the effects of specific materials and external parameters such as energetic and spatial disorders, charge carriers density, localization length, temperature, and applied electric field on the transport properties of charge carriers in disordered organic semiconductors using kMC simulation methods
Summary
Organic polymers that show semiconducting properties because of the weak πbonding along the polymer chain have received widespread attention in the scientific community due to their easy manufacturing and possible applications in modern electronic devices: Organic light-emitting diodes (OLEDs) [1], organic field effect transistors (OFETs) [2,3,4], and organic solar cells [5]. The efficiency of organic disordered semiconductors (ODSs) based electronic devices depends mainly on the transport properties of charge carriers in the semiconductors. The central transport parameter is the drift mobility μ of a charge carrier which is much smaller than that in the inorganic counterparts. There is no consensus on an expression which can uniformly describe the characteristics of the charge carrier mobility in different disordered organic semiconducting polymers. In ODSs the charge carriers are hopping between localized states that are thought to represent the conjugated polymer chain segments that are assumed to be distributed
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