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The effect of extrinsic traps on the motion of charge carriers in an energetically random hopping system, characterized by a Gaussian-shaped density of states function of variance σ, has been studied by Monte Carlo simulations and experiment. The simulations indicate that the presence of a distribution of traps of the same width, but off-set from the intrinsic DOS by an energy E t does not change the basic phenomenology of hopping transport, as revealed by the dependence of the mobility on temperature and field. In quantitative terms, their effect can be accounted for via the replacement of σ with an effective width of the DOS whose square increases linearly with E t and the logarithm of the trap concentration. Experimental results on tri- p -tolylamine doped poly(styrene) containing varying concentrations of trianisylamine, a known hole trap, are in excellent agreement with model predictions. |
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