| Summary: | 碩士 === 義守大學 === 電子工程學系碩士班 === 95 === In this paper, organic light emitting diodes (OLEDs) with the ZnSe and ZnS semiconductor layer as a buffer layer have been fabricated. The results reveal that luminous efficiency of the device can be improved effectively. In addition to make the thin film of mechanism analysis in view of the buffer layer, and to evaluate the luminance-voltage (L-V) characteristics of the devices.
In the investigation, the device structure was ITO/buffer layer/N, N’-diphenyl-N, N’-bis(1-naphthyl-phenyl)-(1, 1’-biphenyl)-4, 4’-diamine (NPB) (40 nm)/tris(8-hydroxyquinolino)-aluminum (Alq3) (60 nm)/LiF (0.7 nm)/Al (200 nm). Using ZnSe as a buffer layer, the driving voltages of OLEDs decrease markedly and the current efficiency is enhanced up to 5.3 cd/A at a current density of 90 mA/cm2. The OLED with a 0.75 nm ZnSe buffer layer has the best power efficiency which has been increased by approximately 55 %. By analyzing the x-ray photoelectron spectroscopy (XPS) spectrum of ITO/ZnSe films, the electron binding energy of atomic outer covering of the In and O increased. It indicated that the charge transporting properties in the OLED with a ZnSe buffer layer are decreased. The injection efficiency is a critical parameter in the L-V characteristics of the devices and depends on the work function of the electrode. Proper insertion of ZnSe buffer layer between indium-tin oxide (ITO) and hole transporting layer (HTL) acting as a hole injection layer will result in a behavior differently from anode and organic materials. The L-V characteristics of the OLEDs further improve.
At the same time, we also attempted to investigate the characteristics of OLEDs with ZnS as a buffer layer. Evidence shows that an OLED with a 1.5 nm ZnS buffer layer has the best power efficiency which has been increased by approximately 16 %, compared with the conventional device.
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