Role of disorder in characterizing the ubiquitous temperature, concentration, and field dependencies of charge transport in molecularly doped polymers

David H. Dunlap

doi:10.1117/12.217305

23 August 1995 Role of disorder in characterizing the ubiquitous temperature, concentration, and field dependencies of charge transport in molecularly doped polymers

David H. Dunlap

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Proceedings Volume 2526, Xerographic Photoreceptors and Photorefractive Polymers; (1995) https://doi.org/10.1117/12.217305
Event: SPIE's 1995 International Symposium on Optical Science, Engineering, and Instrumentation, 1995, San Diego, CA, United States

Abstract

Over the last two decades, experimental investigations of the mobility of photo-injected charges in a wide variety of molecularly doped, pendant-, and main-chain polymers, and vapor deposited molecular glasses have shown that the mobility at high electric fields is universally described by the Poole-Frenkel law, micrometers equals exp(- (Delta) /kT) exp((gamma) (root)E). With few exceptions, the activation energy (Delta) is about 0.5eV, and the Poole-Frenkel factor (gamma) is a function of temperature which follows the empirical relation (gamma) equals B(1/kT - 1/kT₀), where B approximately equals 4 X 10^-4(e²Vcm)^1/2. The remarkable similarity among experiments suggests a mechanism for these dependencies which is largely based on a feature these materials have in common--lack of a crystal structure. Each material consists of a highly disordered array of active molecules, which is believed in turn to give rise to large energetic fluctuations along the conduction pathways. Computer simulations of hopping transport on a disordered lattice have shown behavior in agreement with many aspects of experiment, lending support to the concept of a disorder-based mechanism. To increase our understanding of the high-field effects of disorder, we have developed a self-consistent algorithm with which the field dependence of the mobility in disordered systems may be calculated analytically. We examine the field dependence within this framework, and suggest that the (root)E- dependence may be understood when the theory of Scher and Montroll is applied to a length scale which the hopping matrix may be considered to be of a lower dimensionality.

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David H. Dunlap "Role of disorder in characterizing the ubiquitous temperature, concentration, and field dependencies of charge transport in molecularly doped polymers", Proc. SPIE 2526, Xerographic Photoreceptors and Photorefractive Polymers, (23 August 1995); https://doi.org/10.1117/12.217305

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KEYWORDS

Polymers

Molecules

Algorithm development

Diffusion

Monte Carlo methods

Computer simulations

Crystals

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