Influence of Morphology and Molecular Alignment of a CuPc Layer on the Current-Voltage Characteristics of OLEDs

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Copper phthalocyanine (CuPc), a widely-used semiconductor material, was deposited onto quarts substrates via a vacuum process. SEM and XRD analyses were employed to characterize the structure-controlled CuPc films. As-deposited CuPc thin films were weakly oriented according to the XRD result and were homogeneous. The conductivity of a CuPc thin film was estimated using a four-point probe measurement technique and the values of the conductivity were 8.0 × 10–8–3.5 × 10–7 Ω–1 cm–1. It was observed that thermal annealing had CuPc film well-aligned since thermal annealing could participate to increase the interaction among the CuPc molecules. The interaction between the CuPc molecule and the surface of the substrate may lead to closer stacking of CuPc molecules as well. For well-aligned CuPc thin films, the threshold voltage in the current-voltage characteristics of the ITO/CuPc/Al device was decreased by 20% compared to those of as-deposited CuPc thin films. The current density-voltage (J-V) and luminance-voltage (L-V) characteristics of the present ITO/CuPc/NPD/Alq3/LiF/Al devices were measured to investigate the effect of the alignment of CuPc molecules on the enhancement of hole injection from ITO (Indium Tin Oxide) into HTL (Hole Transporting Layer) through a well-aligned CuPc layer. The luminance is proportional to the current density in the present devices as a similar discrepancy in the L-V characteristic is expected. The higher current density and luminance at a given voltage are shown when a thermally-annealed CuPc layer was placed in the present multilayer devices.
社団法人化学工学会の論文
2005-08-01

Influence of Morphology and Molecular Alignment of a CuPc Layer on the Current-Voltage Characteristics of OLEDs

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