Abstract
Publisher Summary This chapter shows that it is difficult to directly apply the space charge limited current (SCLC) model to organic light-emitting diodes (OLEDs). Although the structure of OLEDs in which organic layers are sandwiched between two electrodes is simple, the light-emitting mechanisms of the device are quite complicated. These mechanisms may be roughly divided into three processes: the carrier injection process from each electrode, the carrier transport process, and the emission process via excitons generated by electron–hole recombination. The chapter assumes a one-dimensional hopping conduction model for the OLED: each emitting molecule corresponds to a hopping site simulating actual charge transfer amongadjacent molecules. Time dependence of carrier, exciton and EL intensity, and distributions of field and carrier density are calculated. Hole and electron densities decrease near the TPD–Alq3 interface. As a result, the density of exciton generation achieves its maximum within 10 nm from the TPD–Alq3 interface. Field distribution because of the space charge effect is not apparent in the TPD bulk. These results suggest that the conduction mechanism in bilayer OLEDs cannot be explained by a typical SCLC conduction model. This model accommodates Fowler–Nordheim emission as an electron injection mechanism. As a result, behavior of current density and EL intensity agree with measured current density and luminance.
Published Version
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