Journal
PHYSICAL REVIEW B
Volume 79, Issue 8, Pages -Publisher
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevB.79.085203
Keywords
current density; diffusion; master equation; organic light emitting diodes; organic semiconductors; semiconductor device models; space-charge limited devices; space-charge-limited conduction
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We present the results of a modeling study of the three-dimensional current density in single-carrier sandwich-type devices of disordered organic semiconductors. The calculations are based on a master-equation approach, assuming a Gaussian distribution of site energies without spatial correlations. The injection-barrier lowering due to the image potential is taken into account, so that the model provides a comprehensive treatment of the space-charge-limited current as well as the injection-limited current (ILC) regimes. We show that the current distribution can be highly filamentary for voltages, layer thicknesses, and disorder strengths that are realistic for organic light-emitting diodes and, that, as a result, the current density in both regimes can be significantly larger than as obtained from a one-dimensional continuum drift-diffusion device model. For devices with large injection barriers and strong disorder, in the ILC transport regime, good agreement is obtained with the average current density predicted from a model assuming injection and transport via one-dimensional filaments [A. L. Burin and M. A. Ratner, J. Chem. Phys. 113, 3941 (2000)].
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