Injection barrier at metal/organic semiconductor junctions with a Gaussian density-of-states

Abstract

We physically model the injection characteristics at the metal/organic semiconductor (M/O) junctions with a Gaussian density-of-states (GDOS). By both analytical and numerical modelling, the charge carrier concentrations at the M/O junctions in an organic rectifying diode (ORD) are calculated. The results demonstrate a special attention required in the application of the Schottky-Mott rule, which defines the injection barrier (IB) for ideal metal/ semiconductor junctions, to M/O junctions. By systematically changing the width of the GDOS that describes the energetic disorder in the organic semiconductor, we show that the edge of the highest-occupied molecular orbitals (HOMO) should be defined as σ k T /2 2 B higher rather than σ 2 from the maximum of the HOMO to keep the consistency of the Schottky-Mott rule. A simple analytical expression for the IB is presented which contains the effect of the disorder in facilitating the charge carrier injection. Simulated current density-voltage characteristics of the ORDs are also presented to support the arguments.

Extraction of built-in potential of organic diodes from current-voltage characteristics

“…4, showing excellent consistency. A similar equation has been reported by different groups in the literature [4,8]. Where S Jung et al arrived at a similar analytical equation for less disordered organic materials with Gaussian density of states.…”

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“…We additionally note that the energetic/structural disorder of materials and its effect on density of states can have a substantial impact on the charge-injection efficiency in organic semiconductors. [37] While the present study adopted the simple Schottky-type injection model, more specific consideration of the injection mechanism will be required for devices with highly disordered active materials (e.g., amorphous polymers).…”

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