Master Degree / Yüksek Lisans Tezleri

Permanent URI for this collectionhttps://hdl.handle.net/11147/3008

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Author: search.filters.author.Okur, SalihSubject: search.filters.subject.Light emitting diodes

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Now showing 1 - 3 of 3
  • Master Thesis
    Characterization of Modified Ito Anode Surfaces With 4 [3-Methylphenyl) Phenyl) Anino] Benzoic Acid for Oled Applications
    (Izmir Institute of Technology, 2011) Yağmurcukardeş, Nesli; Okur, Salih
    This thesis focuses on to improve OLED characteristics of fabricated devices by modifying the ITO (anode) surface using novel carboxylic acid based molecule 4-[(3-methylphenyl)(phenyl)amino]benzoic acid (MPPBA). In this study, commercial ITO substrates were used as anodes. To modify the ITO surface, etched ITO substrates were kept in 1mM MPPBA-ethanol solution. As a hole transport layer (HTL), N,N'-bis(3-methylphenyl)-N,N'-diphenylbenzidine (TPD) or N,N'-Di-[(1-naphthyl)-N,N'-diphenyl]-1,1'-biphenyl)-4,4'-diamine (NPB) small molecules were deposited using an organic evaporator system under the vacuum of 10-6 Torr. Finally, as a cathode contact layer, aluminum thin film of 120 nm was deposited on top of the fabricated organic thin film layers. The final structure of the devices was obtained as ITO /SAM (2nm) /HTL (50nm) /Al (120nm). The current-voltage characteristics of devices of unmodified bare ITO and MPPBA modified ITO substrates were analyzed by using the space charge limited current approach and Thermionic Schottky Emission Models. Additionally, surface characterizations of the SAM modified thin films were carried out using Quartz Crystal Microbalance (QCM), Atomic Force Microscopy (AFM), Kelvin Probe Force Microscopy (KPFM), X-ray Photoelectron Spectroscopy (XPS), Cyclic Voltammetry (CV) and Ultraviolet-visible Absorption Spectroscopy (UV-Vis) techniques. The obtained results reveal that the modification of the ITO surface with MPPBA molecules reduces the barrier height difference between the Fermi level of the anode and HOMO level of the HTL. Hence the hole injection increases while the turn-on voltage decreases. As a result of this process OLED characteristics were improved by using the MPPBA SAM molecules.
  • Master Thesis
    Application of Self Assembled Monolayer Technique To Imporove Hole Transport in Organic Leds
    (Izmir Institute of Technology, 2011) Şeker, Mavişe; Okur, Salih
    This thesis concentrates on the fabrication and characterization of highly efficient Organic Light-Emitting Diode (OLED) with surface modification of indium tin oxide (ITO) anodes by using self-assembled monolayer (SAM) technique. ITO has beencommonly used as an anode for OLEDs, because of the combination of high optical transparency and good electrical conductivity. That is why, ITO substrate is used in this study. On the other hand, the ITO film has often a rough surface, relatively low work function compared with the adjacent organic layer and its surface energy is not well matched to nonpolar organic film. For this purpose, in this work, eleven different SAM molecules were examined to modify ITO surface. Clearly, we aim to reduce the barrier of hole injection, lower the turn-on voltage and improve charge transfer characteristic at the anode-organic film interface using SAM molecules.The ITO work function with the SAM molecules was measured using Kelvin Probe Force Microscopy (KPFM). KPFM measurements were carried out to investigate if there is any increase in ITO work function. Atomic Force Microscopy (AFM) via semi-contact mode was examined the surface morphology of modified ITO. The transmittances of the ITOs with SAM were measured using an UV spectrometer. In addition to these surface analyses, the device performances were characterized by Keithley 236 and High-Resolution Spectrometer. Moreover, Space-Charge-Limited Current (SCLC) and Schottky models were used to analyze the I-V characteristics to calculate hole mobility and barrier heights, respectively.
  • Master Thesis
    Interface Properties of Modified Indium Tin Oxide Based Organic Light Emitting Diodes Withfunctional Aromatic Molecules
    (Izmir Institute of Technology, 2011) Aydın, Hasan; Okur, Salih
    This thesis focused on modification and characterization of ITO substrates with carboxylic acid based self-assembled monolayers to improve OLED device performance. In this study, ITO was used as anode material in OLEDs. In order to modify ITO electrodes, MePIFA and DPIFA aromatic small molecules with double bound carboxylic acid have been used as self-assembly monolayer (SAM). Characterizations of modified ITO and unmodified ITO surfaces were performed via atomic force microscopy and scanning tunneling microscopy. In addition to surface characterization, I-V measurements of the modified and unmodified ITO were taken via spreading resistance microscopy and scanning tunneling microscopy. Moreover, in order to measure change in the surface potential after the modification of ITO surface with MePIFA and DPIFA SAM molecules, Kelvin Probe Force Microscopy was performed. Finally two different configurations of OLEDs devices were fabricated using thermal evaporator system in order to explore the effect of SAM modified ITO on electrical characterization of OLED devices. It was shown that OLED intensity, and turn on voltage were improved compared to OLED devices with unmodified ITO.