Dispersive Aspects of the High-Field Hopping Mobility of Molecularly Doped Solids with Dipolar Disorder


The time-of-flight mobility of photoinjected charges in molecularly doped polymers obeys a Poole-Frenkel law, μ ∝ exp(γ√E), which is commonly viewed as arising from hopping transport among sites with a large degree of energetic disorder. Recent theoretical investigations have focused on long-range correlations that characterize site energies when the dominant mechanism for energetic fluctuations is the interaction of charge carriers with randomly-oriented permanent dipoles of the dopant and host polymer. An exact calculation of the steady-state drift velocity vd for a one-dimensional system with correlated dipolar disorder predicts a Poole-Frenkel law similar to that observed. In order to investigate another feature commonly observed in the high-field measurements, namely, the anomalous dispersion of the current-time transients, we have performed an exact calculation of the field-dependent diffusion constant D for the same dipolar disorder model. In the bulk limit we obtain an expression D = (KT/e)∂vd/∂E that generalizes the normal Einstein relation and predicts a strongly field-dependent diffusion constant.



Keywords and Phrases

Calculations; Charge carriers; Diffusion; Doping (additives); Mathematical models; Organic conductors; Photoconducting materials; Dipolar disorder; Einstein relation; Field dependence diffusion constant; High field hopping mobility; Poole-Frenkel law; Steady state drift velocity; Polymers

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Article - Journal

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© 1997 John Wiley & Sons Inc., All rights reserved.

Publication Date

01 Dec 1997