Transversal and longitudinal diffusion in polar disordered organic materials

Novikov, S. V.; Malliaras, George G.

doi:10.1002/pssb.200562725

Cited by 9 publications

(9 citation statements)

References 7 publications

(12 reference statements)

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“…There are reliable theoretical results showing that the ER cannot hold for the materials having the Gaussian DOS and demonstrating the non-linear average velocity dependence on E or having a non-negligible concentration of charge carriers [2,5]. Invalidity of the Einstein relation in amorphous materials is supported also by computer simulation [21].…”

Section: Experimental Evidence For the Validity Or Invalidity Of mentioning

confidence: 87%

Diffusion of a particle in the Gaussian random-energy landscape: Einstein relation and analytical properties of average velocity and diffusivity as functions of driving force

Novikov¹

2018

Phys. Rev. E

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We demonstrate that the Einstein relation for the diffusion of a particle in the random-energy landscape with the Gaussian density of states is an exclusive one-dimensional property and does not hold in higher dimensions. We also consider the analytical properties of the particle velocity and diffusivity for the limit of weak driving force and establish a connection between these properties and dimensionality and spatial correlation of the random-energy landscape.

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Section: Experimental Evidence For the Validity Or Invalidity Of mentioning

confidence: 87%

Diffusion of a particle in the Gaussian random-energy landscape: Einstein relation and analytical properties of average velocity and diffusivity as functions of driving force

Novikov¹

2018

Phys. Rev. E

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“…Monte Carlo simulation agrees well with the experiments. Indeed, for high temperature the transients are diffusive [51], while for the low temperature a universal behavior emerges ( Fig. 5).…”

Section: Current Transients: Conception Of Universalitymentioning

confidence: 93%

“…It is worth to note that according to the simulation data, the modified Einstein relation Eq. (25) does not hold for the 3D transport in the DG model even for high temperature [51].…”

Section: Current Transients: Conception Of Universalitymentioning

confidence: 96%

Hopping charge transport in organic materials

Novikov

2012

Russ J Electrochem

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General properties of the transport of charge carriers (electrons and holes) in disordered organic materials are discussed. It was demonstrated that the dominant part of the total energetic disorder in organic material is usually provided by the electrostatic disorder, generated by randomly located and oriented dipoles and quadrupoles. For this reason this disorder is strongly spatially correlated. Spatial correlation directly governs the field dependence of the carrier drift mobility. Shape of the current transients, which is of primary importance for a correct determination of the carrier mobility, is considered. A notable feature of the electrostatic disorder is its modification in the vicinity of the electrode, and this modification takes place without modification of the structure of the material. It is shown how this phenomenon affects characteristics of the charge injection. We consider also effect of inter-charge interaction on charge transport.

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“…[21][22][23] In a simplistic sense, if the decay lengths from these experiments are construed as conventional diffusion lengths derived from Einstein's relations L n 2 = (k B T/e) l n s n (where n indicates either a hole or electron, k B is the Boltzmann constant, T is temperature, and e is the charge on an electron), then one can take these L d values as a measure of the ls product. [24] Realistically, the situation prevailing in these systems is complex because the Einstein relations are known to be violated, apart from the observed field-assisted diffusion process [25] and the field-dependent mobility [14] behavior in these systems. We nevertheless observe a correspondence between the observed decay lengths and the ls products in these systems.…”

mentioning

confidence: 99%

“…[26] This deviation can be explained on the basis of interpreting the observed L d in our case as contributions arising largely from the slowest recombination processes under steady-state conditions (deeper traps level) and the lateral character of the diffusion as opposed to the bulk transverse diffusion. [25] The results from our approach where r x,y >> thickness of the polymer film, is largely a characterization of dominant lateral charge-transport processes. MEHPPV is a representative of a disordered system from both the bulk-and lateral-transport perspectives.…”

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confidence: 99%

Direct Estimate of Transport Length Scales in Semiconducting Polymers

Kabra

Narayan

2007

Advanced Materials

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Conjugated semiconducting polymers form a class of materials that utilize facile polymer-processing methods and exhibit practically all the functional phenomena present in traditional semiconductors. [1,2] The successful use of organic semiconductors in optoelectronic applications such as lightemitting diodes [3] (LEDs), organic solar cells, [4] photodetectors, [5] photo-organic field-effect transistors [6] (FETs), optical sensors, [7] and light-emitting FETs [8,9] depend on the development of our understanding of electronic processes to a level comparable to that of their inorganic counterparts. The prevalence of hole and electron transport coexisting has been stressed recently in the context of interesting phenomena observed in these materials. [8,10] The estimation of transport length scales of both carriers-electrons and holes-are important to understand the transport mechanisms as well as to arrive at an optimum design for ambipolar optoelectronic devices such as light-emitting FETs, photo-FETs, and solar cells. The process of charge-carrier generation upon photoexcitation of the polymer semiconductor films is reasonably well documented. The results have been largely interpreted in terms of a primary process such as excitonic mechanisms and subsequent processes involving charge generation and transport.[11] Photocarrier transport studies of the polymer semiconductors are normally carried out using steady-state photoconductivity and transient photoconductivity in sandwich or surface cell configuration. The analysis and interpretation of these results is complicated by the simultaneous presence of both electrons and holes in the same region resulting in recombination processes, trap kinetics, and interfacial processes. The coexistence of drift and diffusion processes, especially in ambipolar systems, and the non-validity of Einstein's relation in the large-field regime makes the extraction of the diffusivity from mobility measurements, especially in anisotropic systems, difficult from standard experimental techniques. [12,13] Even though the standard well-developed methods have yielded accurate quantitative estimates of parameters such as mobility and carrier-lifetime distribution, the method introduced in this paper will complement these measurements with additional insight into properties such as the anisotropy, and correlation between lateral and longitudinal transport processes.Recent observations from our laboratory on polymer-based position-sensitive photocurrent device structures that function over large length scales, also indicate the need for such studies.[7] These position-sensitive planar device structures based on poly(3-hexylthiophene) (P3HT) and poly(2-methoxy-5(2′-ethyl-hexyloxy)-1,4-phenylene vinylene) (MEHPPV) essentially have a pair of front ohmic electrodes and a common back Schottky electrode. The photogenerated holes drift towards the ohmic counter electrode driven by a lateral photovoltage caused by nonuniform illumination of the polymer/Al Schottky interface [7] . In this report, we des...

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Transversal and longitudinal diffusion in polar disordered organic materials

Cited by 9 publications

References 7 publications

Diffusion of a particle in the Gaussian random-energy landscape: Einstein relation and analytical properties of average velocity and diffusivity as functions of driving force

Diffusion of a particle in the Gaussian random-energy landscape: Einstein relation and analytical properties of average velocity and diffusivity as functions of driving force

Hopping charge transport in organic materials

Direct Estimate of Transport Length Scales in Semiconducting Polymers

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