Influence of dipolar species on charge transport in poly[2-methoxy-5-(2′-ethylhexyloxy)-p-phenylene vinylene] (original) (raw)
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Polymers for Advanced Technologies, 2009
The theoretical model of the inter-chain charge carrier mobility in poly[2-methoxy-5-(2(-ethylhexyloxy)-p-phenylene vinylene] (MEH-PPV) doped with polar additive is put forward. The polymer chain states of a charge carrier were calculated by means of diagonalization of a tight-binding Hamiltonian, which includes disorder in both the local energies and transfer integrals. Consequently, the inter-chain charge carrier transport is taking place on a spatially and energetically disordered medium. Because it is believed that the additive does not significantly influence the polymer supramolecular structure, the polymer conformations were simplified as much as possible. On the other hand, the energetic disorder is rigorously described. The transfer rates between the polymer chains were determined using the quasi-classical Marcus theory. The model considered the following steps of the charge carrier transport: the charge carrier hops to a given polymer chain. Then, the charge carrier thermalizes to the Boltzmann distribution over all its possible states on this chain. After that, the charge carrier hops to any possible state on one of the four nearest neighboring chains. The results showed that the inter-chain charge carrier mobility is very strongly dependent on the degree of the energetic disorder. If the energetic disorder is doubled from 0.09 to 0.18 eV, the mobility decreases by two or three orders of magnitude.
Charge carrier transport in poly(2,5-dialkoxy-p-phenylene ethynylene)s
Synthetic Metals, 2003
The charge carrier transport in poly[2,5-dioctyloxy-1,4-diethynyl-phenylene-alt-2,5,-bis(2 0-ethylhexyloxy)-1,4-phenylene], a poly(pphenylene ethynylene) (PPE) derivative, was investigated by time-of-flight (TOF) measurements. The charge transport characteristics in this material are ambipolar, and the transport is dispersive, with high electron (2:2 Â 10 À3 cm 2 V À1 s À1) and hole (1:8 Â 10 À3 cm 2 V À1 s À1) mobilities at room temperature and at low field (3:1 Â 10 4 V cm À1). The mobility strongly depends on the field strength, and is observed to decrease with increasing bias. The positional and energetic disorder parameters were calculated from the temperature and field dependencies of the charge mobility using a Gaussian disorder transport formalism. The positional disorder was found to be larger than the energetic disorder over the entire experimental temperature range, leading to the observed negative field dependence of the carrier mobility.
Modelling of the charge carrier mobility in disordered linear polymer materials
Physical chemistry chemical physics : PCCP, 2017
We introduced a molecular-scale description of disordered on-chain charge carrier states into a theoretical model of the charge carrier transport in polymer semiconductors. The presented model combines the quantum mechanical approach with a semi-classical solution of the inter-chain charge hopping. Our model takes into account the significant local anisotropy of the charge carrier mobility present in linear conjugated polymers. Contrary to the models based on the effective medium approximation, our approach allowed avoiding artefacts in the calculated concentration dependence of the mobility originated in its problematic configurational averaging. Monte Carlo numerical calculations show that, depending on the degree of the energetic and structural disorder, the charge carrier mobility increases significantly with increasing charge concentration due to trap filling. At high charge carrier concentrations, the effect of the energetic disorder disappears and the mobility decreases sligh...
Polymer electronic materials: a review of charge transport
Polymer International, 2006
This article presents an overview of the charge transport phenomenon in semiconducting polymer materials. In these disordered systems both intrinsic and extrinsic parameters play significant roles. In general, π-electron delocalization, interchain interaction, band gap, carrier density, extent of disorder, morphology and processing of materials determine the electrical and optical properties. The chemical structure, especially the role of side groups, is quite important in both physical and processing properties. The nature of charge carriers and their role in charge transport depend on the structure and morphology of the system. Hence in several semiconducting polymer devices, the correlations among structure, morphology and transport are rather strong. The dependence of carrier mobility on temperature and electric field needs to be understood in the framework of competing models based on carrier hopping, trapping/detrapping and tunneling. Exactly what determines the dispersive/nondispersive, polaronic and correlative transport regimes is yet to be quantified. An understanding of the carrier mobility in semiconducting polymers is necessary to optimize the performance of polymeric electronic devices.
Temperature dependence of charge carrier creation in poly(p-phenylene vinylene) [PPV]
Synthetic Metals, 1999
The photocurrent decays measured in poly@-phenylene vinylene) [PPV] from room temperature (RT) down to 77 K in the presence of air traces have been studied. We have observed long-lived decays, between RT and-200 K, which can be fitted to the well known Kohlrausch's law: i&t) = i&O) exp-(t/T)a characteristic of dispersive transport. A detailed temperature dependence study has been carried out to investigate the behavior of the exponent p and the relaxation time 7 in order to understand the origin of the observed complex transport mechanism. At lower temperature, especially below 160 K, a fast component is detected alone, where the slow one is frozen. The associated interpretation is based on a recent work of simulated yield of geminate pair dissociation in an energetically random disorder. Modulated experiments show that both components are superimposed at enough high temperature. In our model, the long-lived contribution is interpreted as being extrinsic due to dissociation of polaron pairs assisted by electronegative defects and the fast one as being intrinsic due to dissociation of excitons assisted by the intrinsic energetic disorder, created by the distribution of conjugation length in PPV.
First-principles determination of charge carrier mobility in disordered semiconducting polymers
Physical Review B, 2010
We propose a theoretical method that can predict carrier mobility in disordered semiconducting polymers and organic semiconductors from first principles. The method is based on nonadiabatic ab initio molecular dynamics and static master equation, treating dynamic and static disorder on the same footing. We have applied the method to calculate the hole mobility in disordered poly͑3-hexylthiophene͒ conjugated polymers as a function of temperature and electric field and obtained excellent agreements with corresponding experimental results. The method could be used to explore structure-mobility relation in disordered semiconducting polymers/organic semiconductors and aid rational design of these materials.
Physical Review B, 2006
We have studied the real and imaginary parts of the complex intrachain mobility of charge carriers on solid samples of ladder-type polymers using time-resolved microwave conductivity measurements. Experiments on samples with a different average polymer chain length show that the motion of charge carriers is limited by the chain ends. The experimental results can be described by one-dimensional diffusive motion along the polymer backbone. The intrachain mobility deduced for an infinitely long ladder-type polymer chain ͑with no barriers to charge transport such as defects or conjugation breaks͒ subject to interchain interactions is 30 cm 2 / V s. This value is 20 times lower than the intrachain mobility found for charges along infinitely long isolated ladder-type polymer chains in dilute solution. Thus we find that interchain interactions in solid samples severely decrease the intrachain charge carrier mobility. However, the intrachain mobility of 30 cm 2 / V s is more than four orders of magnitude higher than mobility values obtained from time of flight measurements reported in the literature. Hence, the performance of ladder-type polymers in optoelectronic devices can be significantly improved.
Charge-carrier transport in disordered polymers
Journal of Polymer Science Part B: Polymer Physics, 2003
General properties of charge carrier transport in disordered organic materials are discussed. Spatial correlation between energies of transport sites determines the form of the drift mobility field dependence. Particular kind of spatial correlation in a disordered material depends on its nature. Mobility field dependences have to be different in polar and nonpolar materials. Different methods of mobility calculation from the shape of photocurrent transient are analyzed. A widely used method is very sensitive to the variation of the shape of the transient and sometimes produces results that effectively masquerade the true dependence of the mobility on electric field or trap concentration. Arguments in favor of the better, more reliable method are suggested. Charge transport in materials containing charged traps is considered without using the isolated trap approximation and this leads to qualitatively different results. They indicate that the effect of charged traps can hardly be responsible for experimentally observed transport properties of disordered organic materials.
The Journal of Physical Chemistry A, 2009
Charge carrier mobility is known to be one of the most important efficiency delimiting factors in conducting polymer-based electronic devices. As the transport mechanism in this class of material is nonconventional, many works have tried to elucidate the charge carrier's interaction with temperature, external electric field, and the collective effects they present. Even though the multiple trap-and-release model is often used to describe these effects, its applicability is known to be restricted to electronic properties. In this work we make use of a modified version of the Su-Schrieffer-Heeger model, the most used method to describe the important properties of conducting polymer in general, to investigate the influence of temperature and carrier densities over the transport mechanisms. We obtained different regimes of temperature and carriers density influence over the systems mobility, consistent with most of the experimental data available.