2024, Hakan Bozkurt, Lazer Kesim PVC Bantlarla Desenleştirilen İç İçe Geçmiş ITO Kaynak ve Akaç Elektrotlu Organik Alan Etkili Transistörlerin Araştırılması (Investigation Of Organic Field-Effect Transistors With Interdigitated ITO Source And Drain Electrodes Patterned By Laser-Cut PVC Tapes)

Abstract. In this thesis aimed to produce a light-emitting vertical transistor at first. However, due to unsuccessful attempts, it was planned to produce a horizontal transistor for testing purposes and this transistor was tried to be optimized. Later, vertical efforts and horizontal optimizations and laser cutting experiences were brought together and main topic were changed later. Laser cutting was tried to achieve a low-cost fabrication technique for electrode pattern creation for the wet etching process. Interdigitated ITO Source & Drain electrodes were prepared then P3HT as OSC and PMMA as dielectric material, solution-processed and spin-coated respectively. Al top electrode was coated using the PVD technique. ITO(S&D)/P3HT(OSC)/PMMA(DM)/Al(G) conventional OFET architecture was fabricated and optimized due to layer coating parameters and laser configurations. Measurements were done in an inert atmosphere inside a glovebox system. Fabricated OFETs can work for both depletion and enhancement modes. Mobilities were increased and Threshold Voltages were decreased due to optimizations and the current levels at zero gate voltage were reduced. P-type depletion mode was rare for both in the market and at the literature. This type of OFETs may be a good candidate for display applications.

2022, Oğuzhan Çimen, Organik Fotonik Sistemler için Poliüretan/Akrilat Enkapsülasyon Malzemesi Sentezi ve Karakterizasyonu (Synthesis and Characterization of Polyurethane/ Acrylate Encapsulation Materials for Organic Photonic Systems)

Abstract. In this thesis, polyurethane acrylate encapsulation coating materials were synthesized to extend the life of organic photonic systems. Structural characterization of synthesized materials for coating formulations was performed by FTIR, 1H NMR, 13C NMR. In coating form, thermal characterization were carried out via DSC and TGA and mechanical tests were carried out according to ASTM standards. The contact angles of the coatings were measured and the barrier properties were demonstrated by the calcium test. The lowest water vapor transmission rate value was found at 3.25×10^-2 g/m².day with the 3 µm thickness of K-HBUAc-5 structure. The application of the same structure with a thickness of 10 µm allowed to reach 7.9×10^-3 g/m².day value. The glass transition temperature value for K-HBUAc-5 is 73.1 ^oC, the contact angle is 61^o and the gel content is 96%. The transmission rate values measured at 3 µm thicknesses of the other five materials are in the order of 10^-1 g/m².day. The transmission rate values measured at 3 µm thicknesses of the other five materials are at the level of 10^-1 g/m².day. The measured transmission rates for K-HBUAc-5 indicate that it can be used with different modifications in organic light-emitting diodes or in combination with inorganic thin films, while it can be used alone in organic photovoltaic devices.

2021, Shirin Siyahjani Gültekin, Nanokarbon Elektrot ve Polimer Jel Elektrolit Tabanlı Süperkapasitörler (Supercapacitors Based on Nanocarbon Electrode And Polymer Jel Electrolyte)

Abstract. In this thesis, development of new electrolyte and electrode materials for Electrochemical Double Layer Capacitors (EDLC), preparation and performance analysis of EDLC devices with those components have been carried out. Etheric and/or allylic-group-functionalized ionic liquid and dielectric polymers have been used to obtain GPEs. Effects of etheric and allylic groups of Cations on ionic conduction and electrochemical stability of GPE films and working voltage, ESR, capacitance and energy density of EDLC devices have been investigated. Furthermore, new electrodes have been prepared by using carbon nano materials (single walled carbon nanotube (SWCNT) and reduced graphene oxide (RGO)). Effects of preparation method, surface area and pore size for electrodes on ESR and capacitance values of EDLC devices have been investigated. Finally, EDLC devices have been fabricated with each electrolyte and electrode materials prepared and characterized previously. All EDLC devices have been tested and analysed by using cyclic voltammetry, electrochemical impedance analysis and charge-discharge analysis. In addition to these, power and energy density of each devices have been calculated by using corresponded equations and performance of all devices have been compared with each other and similar structures in the literature.

2020, Erkan Aksoy, Organik Fotonik Sistemlerde Kullanilabilecek Perilendiimit Türevlerinin Sentezi ve Fotofiziksel Karakterizasyonu  (Synthesis And Photophysical Characterization Of Perylenediimide Derivatives For Organic Photonic Systems)

Abstract. In this thesis, acetylene-bridged PDI and PTE derivatives with different volumetric groups, which have been proven to be used in Organic Photonics Technologies with experimental data, were synthesized and their structures were characterized by FTIR, 1H-NMR, 13C-NMR, GS-MS-ASAP and MALDI-TOF. In addition to the photophysical and electrochemical properties of PTE and PDI derivatives, as well as the characterizations of the excited singlet state exciton and photoinduced absorption regions (PIA) were performed by TCSPS, ultra-fast time resolved PL with high sensitivity iCCD camera and fs-pump probe TAS techniques. All synthesized perylene derivatives have 90% quantum yields, 3-6 ns fluorescence lifetimes (τ) and ≥300°C decomposition temperatures. In electrochemical measurements, PDI derivatives (except PDI6) exhibited only reduction peaks while PTE derivatives exhibited both reduction and oxidation peaks. Due to the bipolar property of the PDI6 derivative, both the reduction and the oxidation peak were determined. The interaction between the electron donor and acceptor groups in PDI6 structure changes depending on the solvent; fast and permanent electron transfer in chloroform environment, a reversible and slow electron transfer in the toluene medium. The acetylene and phenyl acetylene bridges placed in the bay positions of the PDIs reduced their reduction potential (~ 0.05 to 0.10V) and shifted the absorption wavelengths to the red region of 25 and 51 nm, respectively.  It has also been shown that some PTE and PDI derivatives can be used as wavelength converters.

2018, Özlem Kap, Structural and electronic properties of organic layers on Au(111) (Organik katmanların Au(111) üzerinde yapısal ve elektronik özellikleri)

Abstract. Self-assembled monolayers (SAMs) have attracted attention due to their chemical and structural properties providing numerous new applications such as molecular electronics and electrochemistry. SAMs were optimized by experimental techniques including Scanning Tunneling Microscope (STM), Scanning Tunnelling Spectroscopy (STS), X-Ray Photoelectron Spectroscopy (XPS), Polarization-Modulation Infrared Reflection-Absorption Spectroscopy (PM-IRRAS), Cyclic Voltammetry (CV), Electrochemical Impedance Spectroscopy (EIS). The first part of this dissertation deals with the dynamic behaviour of decanethiol SAMs. The dynamic behaviour alkanethiols SAM is unique for its configuration giving indirect evidence for the structural ordering within the formation. Structural stability of decanethiol (decanesulfonates) SAMs were investigated by space- and time- resolved STM. Decanesulfonate phase shows less dynamic behaviour and is structurally more stable compared to the decanethiol phases. The second part of this dissertation describes the binding properties of alkyne molecules adsorbed on gold. Alkyne oxidation occurs at ambient conditions but it is found that unlike thiols, ordered alkyne SAM structure has still chemical bonding between carbon and gold. Alkyne SAMs are good candidates for the ambient molecular electronics application. The last part of this dissertation presents the study of a monolayer of a Ru(II) complex which is prepared on gold substrate. With the help of STM and XPS methods, the ordered structure and binding properties of the CS28 molecules were characterized by providing a deeper insight into the carboxyl and sulfur groups binding affinity to gold substrate. CV and EIS methods were used to compare the adsorption properties and charge transfer process with the bare gold substrate and SAMs.

2017, Saliha Öner, Organik Fotonik Sistemlerde Kullanilabilecek Bipolar Konak Malzeme Sentez ve Karakterizasyonları (Synthesis and Characterization of Bipolar Host Materials For Organic Photonic Systems)

Abstract. In this thesis, four p-type host material and four bipolar host material were synthesized. The structural characterizations of the synthesized molecules were carried out by FTIR, 1H-NMR ve 13C-NMR spectroscopies. In the p-type host materials, electon donating carbazole (D) groups and bulky tetraphenysilane groups were used together. As a result, hole conducting p-type host materials with high glass transition temperatures (Tg ≥ 120 °C) were obtained. Bipolar host materials are composed of electron donating carbazole and electron accepting (A) triazine groups. Tetraphenylsilane groups were attached between the donor and acceptor groups, and high tiplet energy (ET ≥ 2.9 eV) bipolar host molecules were obtained because of the interruption of the conjugation by the tetraphenylsilane groups.

Tert-butyl groups were attached to the 3,6 positions of the carbazoles to increase the solubility of the molecules and as a result, host materials which are soluble in most of the organic solvents (chloroform, toluene, EtOAc etc) were obtained. The photophysical properties of the synthesized molecules were studied by UV-Vis absorption and photoluminescence (PL) spectroscopies and electrochemical properties were studied by cyclic voltammetry (CV) measurements.

2017, Halide Diker, Organik Fotonik Sistemlerde Kullanilabilecek Grafen Oksit Sentezi ve Karakterizasyonu (Synthesis and Characterization of Graphene Oxide for Photonic Applications)

Abstract. Graphene oxide (GO) was obtained by using Tour method. Reduction of obtain GO (rGO) was carried with Vitamin C (VitC), and structural, morphological and electrical results obtained were compared with hydrazine reduced samples. X-ray photoelectron spectrometry, X-ray diffraction spectrometry, Raman spectrometry, UltraViolet-visible spectrophotometry, Fourier infrared spectroscopy, thermal gravimetric analysis, atomic force microscope and surface resistivity measurement systems were used during characterization. For the samples which were prepared with the use of VitC under basic and neutral reaction conditions, the highest carbon:oxygen (C:O ) ratio was 6.02 and 5.37, respectively, and for the latter, the surface resistivity of the film prepared by dropping-drying is 0.25 Mohm/sq. These values were 8.35 ve 0.71 Mohm/sq, respectively for the hydrazine medium. The reduction of GO by hydrazine on the film surface resulted in transmittance loss and the surface resistivity of this film was 337ohm/sq. Independent from the reduction agent, dispersion stability of rGO samples was very low. Therefore, GO samples were modified by primary, secondary and alcohol amine derivatives (mGO) and C:O ratio of 7.56 was achieved. With the increase in alkyl chain length of the reactant amine, the dispersion stability of mGOs in polar aprotic solvents was increased while a decrease was obtained in polar protic solvents. Composite films of the synthesized rGO and mGO derivatives with poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate were prepared. The surface resistivity values of these composites were in the order of Mohm/sq and optical transmittance of > 90% was obtained in all of the films.

Abstract.This work comprises different solution process approaches for obtaining large area white organic light emitting diodes (WOLED). Spin coating and doctor blade were used for the fabrication of large area WOLEDs. In addition, newly synthesized two ruthenium and three iridium complexes were used to investigate their potential for the WOLEDs.Generation of white light is realized by using one of the triplet harvesting method (phosphorescent/fluorescent (F/P) approach). Hence, white light was obtained from the residual blue phosphorescence of the sensitizer, the sensitized orange-red fluorescence is due to triplet-to-singlet energy transfer, and the instantaneous fluorescence results from singlet–singlet transfer. Two ruthenium complexes labeled as CS91 and CS93, and three iridium complexes labeled as CS137, CS138 and CS139 were used as an orange-red emitter and yellow in an OLED for investigation of their potentials as an emitter material for WOLEDs.

Finally, the highly efficient WOLED were used for enlarge the active area by using spin coating and doctor blade techniques. WOLED panel (63mm x 100) with active area of 30mm x 70mm were obtained by using doctor blade.

Abstract. In this thesis organic and organic:inorganic hybrid UV photodetectors with enhanced photocurrent responses are prepared and characterized optically and electrically. With this aim, a fluorene type polymer, poly(9,9-dioctyl fluorenyl-2,7–yleneethynylene (PFE) is chosen as the p-type material and the effects of different n-type materials are observed. As a summary,(i)      PFE is doped with buthylnapthalenedimide (BNDI) organic semiconductor,

(ii)     PFE:BNDI is doped with titaniumdioxide (TiO2) inorganic semiconductor,

(iii)    PFE is doped with zincoxide (ZnO) metaloxide inorganic semiconductor and

(iv)   PFE:BNDI is doped with ZnO metaloxide semiconductor

are used as active layer in conventional and/or inverted type photodetectors. Maximum photoresponses from these studies were; 410 mA/W, 597 mA/W, 375 mA/W and 651 mA/W, respectively.