Browsing by Author "Bozkurt, Hakan"

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Citation - WoS: 19
Citation - Scopus: 20
Controlling the Distribution of Oxygen Functionalities on Go and Utilization of Pedot:pss-Go Composite as Hole Injection Layer of a Solution Processed Blue Oled
(Elsevier Ltd., 2017-04) Diker, Halide; Durmaz, Gamze Belkis; Bozkurt, Hakan; Yeşil, Fatih; Varlıklı, Canan; 01. Izmir Institute of Technology; 04.04. Department of Photonics; 04. Faculty of Science
Graphene oxide (GO) was synthesis by Tour method. Particle size distribution effects of raw graphite on the resulting structural, morphological, optical and electrical properties of GO samples and their poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) composites are studied for the graphite particle distributions of <150, 45–75 and 25–45 μm. It is determined that particle size of raw graphite have an impact on oxidation degree, the chemical nature of oxygen functional groups on GO and it also affects the lateral size of obtained GO. PEDOT:PSS-GO composites are utilized as hole injection layer (HIL) in a solution process blue organic light emitting diode. Presence of GO caused negative differential resistance (NDR) and NDR intensity was decreased with the decrease in lateral size of GO, increase in the graphite particle size and carboxyl% of obtained GO. All PEDOT:PSS-GO composite based devices presented better performance than the bare PEDOT:PSS based reference device. The maximum luminous and external quantum efficiency values of the device that contain HIL of PEDOT:PSS-GO(150) were more than 40% and 50% higher than that of the reference, respectively. Two folds of increase in these performance values were able to be reached with the concentration optimization of GO/150 in PEDOT:PSS.
Citation - WoS: 14
Citation - Scopus: 13
Dispersion Stability of Amine Modified Graphene Oxides and Their Utilization in Solution Processed Blue Oled
(Elsevier Ltd., 2020) Diker, Halide; Bozkurt, Hakan; Varlıklı, Canan; 01. Izmir Institute of Technology; 04.04. Department of Photonics; 04. Faculty of Science
Graphene oxide (GO) was modified with amine derivatives which contain short (SACA) and long (LACA) alkyl chains. SACAs were n-propylamine, dipropylamine, propanolamine and LACAs were 2-ethylhexylamine, di-hexylamine, dioctylamine, and 1,12-diaminododecane and modified GOs (mGOs) were named as nPRYLA-GO, DPRYLA-GO, PRPOHA-GO, 2EHA-GO, DHA-GO, DOA-GO, and DADOD-GO, respectively. Amine modification resulted in approximately 2-folds of decrement in d-spacing of GO (8.36 angstrom). The C:O ratio, N% and d-spacing values were increased as the alkyl chain length of amine source increased. Except for PRPOHA-GO, all of the mGOs were thermally stable until 100 degrees C. All mGOs were dispersed in dimethylformamide (DMF), ethylene glycol (EG) and isopropyl alcohol (iPA). Regardless of their structural differences, all of the mGOs formed stable dispersions in DMF, whereas SACA-mGOs and LACA-mGOs were compatible with EG and iPA, respectively. DMF, EG and iPA dispersions of DOA-GO, 2EHA-GO, nPRYLA-GO and PRPOHA-GO were doped in Al4083 and prepared composites were utilized as hole transport layer in solution processed blue OLEDs. Ground state energy levels of Al4083:DOA-GO, Al4083:EG, Al4083:PRPOHA-GO, Al4083:2EHA-GO and Al4083:nPRYLA-GO extracted from their X-ray photoelectron spectra were 0.49 eV, 0.67 eV, 0.91 eV, 0.98 eV and 1.00 eV below the work function of ITO, respectively. Among all Al4083:mGOs, the best device performance was obtained with the device that contains Al4083:DOA-GO (in EG), which presented 1.6, 1.7 and 1.5 fold enhancements in current, power and external quantum efficiencies, respectively, compared to those of Al4083:EG based device.
Citation - WoS: 3
Citation - Scopus: 2
Fabrication and Characterization of a Solution Processed Flexible Thermal Sensor by Using Chemically Synthesized Go and Rgo
(Institute of Electrical and Electronics Engineers Inc., 2019) Bozkurt, Hakan; Diker, Halide; Varlıklı, Canan; 01. Izmir Institute of Technology; 04.04. Department of Photonics; 04. Faculty of Science
Graphene oxide (GO) was reduced by ascorbic acid which is an environmental-friendly reductant and obtained sample was named as reduced GO (rGO). Stable dispersions of GO and rGO were prepared in N,N-Dimethylformamide (DMF). Compared to GO sample, rGO was determined to have more thermal stability, smaller sheet size and lower surface energy. GO and rGO dispersions were drop-casted on aluminum (Al) coated acetate substrate and used as thermal sensor. Fabricated sensors were tested from 25 °C to 150 °C. The sensors fabricated with GO, were not stabile against driven temperature changes. However, rGO ones, presented no thermal hysteresis effect after the first heating step. This sensor (Al/rGO/Al) acted like an NTC (Negative Temperature Coefficient) thermistor. The resistance of the rGO sensor was changed between 42 k? to 25 k? depending on the test temperature range (25 °C to 150 °C). Average beta value was calculated as 519.7649 K. © 2019 IEEE.
Investigation of Organic Field Effect Transistors With Interdigitated Ito Source and Drain Electrodes Patterned by Laser Cut Pvc Tapes
(01. Izmir Institute of Technology, 2024) Bozkurt, Hakan; Varlıklı, Canan; Özçelik, Serdar; 04.01. Department of Chemistry; 04.04. Department of Photonics; 04. Faculty of Science; 01. Izmir Institute of Technology
Bu tezde başlangıçta ışık yayan dikey bir transistör üretmeyi amaçlamıştık. Ancak, başarısız denemeler sonucunda, test amaçlı yatay bir transistör üretme kararı alınmış ve bu transistörün optimizasyonu üzerinde çalışılmıştır. Daha sonra dikey transistör üretimi, yatay optimizasyonlar ve lazer kesim teknikleri bir araya getirilerek araştırmanın ana odağı değiştirilmiştir. Islak aşındırma süreci ile elektrot desenlemek için düşük maliyetli bir üretim yöntemi olarak lazer kesim denenmiştir. İç içe geçmiş (taraklı) ITO kaynak ve drenaj elektrotları hazırlanmış, ardından organik yarıiletken olarak P3HT ve dielektrik malzeme olarak PMMA sırasıyla dönü kaplama yöntemiyle kaplanmıştır. Üst elektrot olarak da alüminyum (Al), fiziksel buhar biriktirme tekniği kullanılarak kaplanmıştır. Nihai cihaz yapısı olarak ITO(KveA)/P3HT(Organik Yarıiletken)/PMMA(Dielektrik Malzeme) /Al(Kapı) şeklinde geleneksel bir OFET mimarisi oluşturulmuştur. Üretim süreci, katman kaplama parametreleri ve lazer kesim konfigürasyonları göz önünde bulundurularak en iyileştirilmiştir. Elektriksel ölçümler, soy atmosfer koşullarında bir eldivenli kutu sistemi içinde gerçekleştirilmiştir. Üretilen OFET'ler hem tükenme hem de geliştirme modlarında çalışabilmiştir. Yapılan en iyileştirmeler sonucunda yük taşıyıcı hareketliliği artırılmış, eşik gerilimi düşürülmüş ve sıfır kapı geriliminde akım seviyeleri azaltılmıştır. P-tipi tükenme modu OFET'ler, hem ticari uygulamalarda hem de akademik literatürde nadir görülür. Bu tür transistörlerin ekran uygulamaları için umut vadeden bir aday olabileceği düşünülmektedir.