Comparison of charge transport models in molecularly doped polymers

Schein, L. B.

doi:10.1080/13642819208204920

Cited by 246 publications

(98 citation statements)

References 36 publications

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“…20,26 The data do not cover a wider range of temperatures or fields than previous reports, and therefore are not significantly more stringent tests of the GDM, nor do the results completely rule out other models that approximate the exp(␤ͱE) dependence. 14,[23][24][25]27,38 The purpose of the present study is to test the dipolar disorder models in systems with large concentrations of highly polar chromophores and also to find a means to improve the sensitivity of photorefractive polymers.…”

Section: Discussionmentioning

confidence: 99%

“…Transport models are mostly distinguished by the form of charge transfer between transport molecules ͑e.g., small polaron 18 or adiabatic 19 hopping͒, by the distributions of site energies and positions, 20,21 and by the formalism for combining hopping events to calculate bulk transport. 20,22,23 Recent attention has been focused on reproducing the exp(␤ͱE) Poole-Frenkel form which the current models reproduce only over a limited range of electric fields, much more limited than the available data require. [23][24][25] Many recent results have been interpreted within the framework of the Gaussian disorder model ͑GDM͒ developed by Bässler and co-workers.…”

Section: Introductionmentioning

confidence: 99%

“…20,22,23 Recent attention has been focused on reproducing the exp(␤ͱE) Poole-Frenkel form which the current models reproduce only over a limited range of electric fields, much more limited than the available data require. [23][24][25] Many recent results have been interpreted within the framework of the Gaussian disorder model ͑GDM͒ developed by Bässler and co-workers. 14,20,26 The GDM is based on the assumption that charge transport occurs by activated hopping with a Miller-Abrahams asymmetric hopping probability 19 through a manifold of localized states with superimposed energetic ͑diagonal͒ and positional ͑off diagonal͒ disorder with Gaussian distributions.…”

Section: Introductionmentioning

confidence: 99%

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Effect of dipolar molecules on carrier mobilities in photorefractive polymers

Goonesekera

Ducharme

1999

Journal of Applied Physics

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The grating formation speed in photorefractive polymers is greatly reduced by highly polar molecules incorporated by necessity in large concentrations to produce large diffraction efficiency and two-beam energy coupling gain. The random electric fields generated by these dipoles interfere with charge transport by increasing the width of the hopping site energy distribution and thus greatly reducing the carrier mobility and the photorefractive speed. We conducted transport studies of several model systems consisting of combinations of two polymer binders, six charge transport agents ͑four for holes and two for electrons͒, and varying concentrations of two highly polar electro-optic chromophores. The results confirm that carrier mobility is greatly reduced in the presence of polar molecules in accordance with the predictions of models of hopping transport in the presence of dipolar disorder. The randomly positioned and oriented dipoles increase the width of the hopping site energy distribution by an amount proportional to the square root of the dipole concentration and to the strength of the dipole moment. The results also show that transport agents with smaller dipole moments reduce the sensitivity to the dipolar effect. The photorefractive speed may therefore be increased by using transport agents with small dipole moments.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Effect of dipolar molecules on carrier mobilities in photorefractive polymers

Goonesekera

Ducharme

1999

Journal of Applied Physics

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“…The discussion was, to much extent, provoked by the reports on the apparent decrease of the drift mobility with rising electric field at relatively high temperatures and low field strengths in disordered organic materials. 3,4,5,6,7,8,9,10 This apparent decrease of the mobility with increasing electric field was reported to be succeeded by the increase of the mobility at higher field strengths. However, the self-consistent effective-medium theory for drift and diffusion at low electric fields 11 does not show any decrease of the mobility with increasing field.…”

Section: Introductionmentioning

confidence: 99%

Hopping conduction in strong electric fields: Negative differential conductivity

et al. 2008

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Effects of strong electric fields on hopping conductivity are studied theoretically. Monte-Carlo computer simulations show that the analytical theory of Nguyen and Shklovskii [Solid State Commun. 38, 99 (1981)] provides an accurate description of hopping transport in the limit of very high electric fields and low concentrations of charge carriers as compared to the concentration of localization sites and also at the relative concentration of carriers equal to 0.5. At intermediate concentrations of carriers between 0.1 and 0.5 computer simulations evidence essential deviations from the results of the existing analytical theories.The theory of Nguyen and Shklovskii also predicts a negative differential hopping conductivity at high electric fields. Our numerical calculations confirm this prediction qualitatively. However the field dependence of the drift velocity of charge carriers obtained numerically differs essentially from the one predicted so far. Analytical theory is further developed so that its agreement with numerical results is essentially improved.

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“…[1][2][3] There has been remarkable success in the development of quantitative physical models of charge transport. The most notable and widely used models are the Gaussian disorder model ͑GDM͒ developed by Bässler and co-workers 1 and the small polaron models [4][5][6] though there are several other models worth consideration.…”

Section: Introductionmentioning

confidence: 99%