| Summary: | 碩士 === 國立成功大學 === 電機工程學系碩博士班 === 91 === Since Tang and Van Slyke reported efficient electroluminescence from a bilayer organic device in 1987, organic light emitting devices (OLEDs) have attracted great attention due to their potential toward the fabrication of large-area displays. To achieve efficient electroluminescence, OLEDs based on some molecules, in general, have separate layers of a hole transport material (HTM) and an emitting electron transport material (ETM). Naphtyl-substituted benzidine derivative (NPB) and tris (8-hydroxyquinoline) aluminum (AlQ3) are often been used as a HTM and an emitting ETM.
In this study, we try to deposit nano-scaled NPB and AlQ3 using a thermal evaporation system, separately. In simple sandwich structure, ITO/organic/Al, we try to investigate the electrical (I-V) characteristics of these organic thin films. The experimental results for NPB films show that the peak voltage (the voltage at which the current reaches its maximum values) increases with increasing the thickness of the organic films at forward bias. On the other hand, it also shows that the breakdown voltage (the voltage at which the current reaches zero value) increases with increasing the thickness as operating at reverse bias. As the thickness of the device is thin, the dominated current is the tunneling current. On other hand, as the thickness is thicker, the dominated current is the drift current. The current is influenced by the barrier of the interface energy. We found a peculiar image of low current in ITO/NPB (40 nm)/ Al device and we do not clear that the real cause. It should be studied for more research. On the other hand, the I-V characteristics of the devices will also be affected by the external electrical field.
As for the devices consisted of AlQ3, the electrical field decreases with increasing the thickness of the organic films at reversed bias and increases with increasing the thickness and finally saturates at forward bias.
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