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Öğe Characterization of organic solar cells using semiconducting polymers with different bandgaps(Walter De Gruyter Gmbh, 2019) Borazan, Ismail; Altin, Yasin; Demir, Ali; Bedeloğlu, AyşePolymer-based organic solar cells are of great interest as they can be produced with low-cost techniques and also have many interesting features such as flexibility, graded transparency, easy integration, and lightness. However, conventional wide bandgap polymers used for the light-absorbing layer significantly affect the power conversion efficiency of organic solar cells because they collect sunlight in a given spectrum range and due to their limited stability. Therefore, in this study, polymers with different bandgaps were used, which could allow for the production of more stable and efficient organic solar cells: P3HT as the wide bandgap polymer, and PTB7 and PCDTBT as low bandgap polymers. These polymers with different bandgaps were combined with PCBM to obtain increased efficiency and optimum photoactive layer in the organic solar cell. The obtained devices were characterized by measuring optical, photoelectrical, and morphological properties. Solar cells using the PTB7 and PCDTBT polymers had more rough surfaces than the reference cell using P3HT. The use of low-bandgap polymers improved I-sc significantly, and when combined with P3HT, a higher V-oc was obtained.Öğe Graphene and graphene oxide-coated polyamide monofilament yarns for fiber-shaped flexible electrodes(Taylor & Francis Ltd, 2019) Tas, Mahmut; Altin, Yasin; Bedeloğlu, AyşeIn this study, polyamide monofilament yarn of 3000 tex was coated with graphene oxide (GO) nanomaterial using dip-coating method. The graphene oxide layer was then reduced with green chemical reduction method, resulting in a reduced graphene oxide-coated monofilament yarn. The properties of the graphene oxide and reduced graphene oxide-coated polyamide monofilament yarns were characterized by performing physical, electrical, optical, and morphological investigations. The lowest sheet resistance was measured from seven-layer graphene-coated polyamide monofilament yarn as 3.09 k omega/sq. Moreover, it was measured that 90 degrees and 180 degrees bent seven-layer graphene-coated polyamide monofilament yarns had 3.57 and 3.81 k omega/sq sheet resistance, respectively. Additionally, while PA monofilament yarn has 73.5% transmittance at 550 nm; seven-layer GO and seven-layer graphene have 18.8 and 4.5%, respectively, as expected. On the other hand, the contact angle increased with the reduction of graphene oxide layer on monofilament yarn. The fabricated graphene-coated polyamide monofilament yarns can be used in electrotextiles, solar cells, sensors, and OLEDs as fiber-shaped flexible electrodes.Öğe Graphene oxide and zinc oxide decorated chitosan nanocomposite biofilms for packaging applications(Walter De Gruyter Gmbh, 2020) Terzioğlu, Pınar; Altin, Yasin; Kalemtaş, Ayşe; Bedeloğlu, AyşeRecently, due to sustainable development and environmental protection policies, there is increasing interest in the development of new biodegradable polymer-based multifunctional composites. Chitosan is one of the most remarkable and preferred biopolymers, which is environmentally friendly as well as renewable, biocompatible, and inexpensive. Though it has a wide range of potential applications, the major limitation of chitosan - the problem of poor mechanical performance needs to be solved. In this work, graphene oxide was first produced and then used to manufacture a chitosan/graphene oxide/zinc oxide composite film through a casting method. The properties of the chitosan film and the chitosan/graphene oxide/zinc oxide composite film were investigated using Fourier transform infrared spectroscopy, mechanical, thermal gravimetric, and ultraviolet (UV)-visible spectroscopy analyses. The results showed that the incorporation of graphene oxide and zinc oxide into the chitosan matrix resulted in enhanced mechanical properties and thermal stability of chitosan biocomposite films. The graphene oxide- and zinc oxide-reinforced chitosan film showed 2527 MPa and 55.72 MPa of Young's modulus and tensile strength, respectively, while neat chitosan showed only 1549 MPa and 37.91 MPa of Young's modulus and tensile strength, respectively. Conversely, the addition of graphene oxide decreased the transmittance, notably in the UV region.Öğe Graphene oxide modified carbon fiber reinforced epoxy composites(Walter De Gruyter Gmbh, 2020) Altin, Yasin; Yilmaz, Hazal; Unsal, Omer Faruk; Bedeloğlu, AyşeThe interfacial interaction between the fiber and matrix is the most important factor which influences the performance of the carbon fiber-epoxy composites. In this study, the graphitic surface of the carbon fibers was modified with graphene oxide nanomaterials by using a spray coating technique which is an easy, cheap, and quick method. The carbon fiber-reinforced epoxy matrix composites were prepared by hand layup technique using neat carbon fibers and 0.5, 1 and 2% by weight graphene oxide (GO) modified carbon fibers. As a result of SEM analysis, it was observed that GO particles were homogeneously coated on the surface of the carbon fibers. Furthermore, Young's modulus increased from 35.14 to 43.40 GPa, tensile strength increased from 436 to 672 MPa, and the elongation at break was maintained around 2% even in only 2% GO addition.Öğe Poly(vinylidene fluoride) nanofiber-based piezoelectric nanogenerators using reduced graphene oxide/polyaniline(Wiley, 2020) Unsal, Omer Faruk; Altin, Yasin; Bedeloğlu, AyşeRecently, piezoelectric nanogenerators have received great interest as they can convert waste mechanical and radiative energy to electricity and can be used in self-energy generating systems and sensor technologies. In this study, electrospun poly(vinylidene fluoride) (PVDF) nanofiber-based piezoelectric nanogenerators with reduced graphene oxide (rGO), polyaniline (PANI), and PANI-functionalized rGO (rGOPANI) have been developed. Two different types of nanofiber mats were produced: First, rGO- and rGOPANI-doped PVDF nanofiber mats and second, rGO, PANI and rGOPANI-spray-coated PVDF nanofiber mats that have worked as nanogenerators' electrodes. Then, characterizations of samples were performed in terms of piezoelectricity, Fourier transform infrared (FTIR) spectrophotometric, X-ray diffractions (XRD), and scanning electron microscopy analyses. FTIR and XRD results confirmed that piezoelectric beta-crystalline phase of PVDF occurred after the electrospinning process. Besides, maximum output voltages were obtained as 7.84 and 10.60 V for rGO-doped PVDF and rGOPANI-coated PVDF nanofiber mats, respectively. As a result, the doped nanofibers were found to be more successful due to the higher device accuracy in sensor technologies compared with spray-coated samples. However, spray-coating method proved to be more suitable technique for the production of nanogenerators on an industrial scale in terms of fast and large-scale applicability. (c) 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 48517.Öğe Polyimide-coated fabrics with multifunctional properties: Flame retardant, UV protective, and water proof(Wiley, 2019) Hicyilmaz, Ayse Sezer; Altin, Yasin; Bedeloğlu, AyşeMultifunctional technical textiles are of great interest both by industry and academia and these products are considered as high value-added products that contribute to the economies of countries. In this study, polyamic acid (PAA) was synthesized through polycondensation of pyromellitic dianhydride (PMDA) and 4,4 '-oxydianiline (ODA) in dimethyl acetamide (DMAc) at low temperature. Then, PAA was coated onto woven cotton and polyester fabric by padding technique. Finally, polyimide (PI)-coated multifunctional cotton and polyester fabrics were obtained by an easy coating technique and low-temperature imidization. Thus, low cost, easily accessible and widely used cotton and polyester fabrics were converted to high-performance textile products, which are flame retardant, UV protective, acid resistant, and waterproof. The chemical, thermal, morphological, optical, mechanical, wettability, chemical resistance, and flame retardancy properties of developed fabrics were investigated. Optical results showed that both PI-coated cotton and polyester fabrics are UV-A protective compared to noncoated fabrics. Moreover, PI-coated samples have high contact angles which are 111.43 degrees and 113.40 degrees for PI-coated cotton (PI-c-C) and PI-coated polyester (PI-c-PET), respectively. Young's modulus of PI-c-PET fabrics increased four times more than noncoated polyester fabric. PI coating changed the burning behavior of both cotton and polyester fabrics in a positive way. All the test results showed that these developed multifunctional textile products might find an application in different industrial areas such as automotive, aerospace, protective clothing, and so on due to easy and inexpensive production techniques and also superior properties. (c) 2019 Wiley Periodicals, Inc.Öğe Reduction of graphene oxide thin films using a stepwise thermal annealing assisted by L-ascorbic acid(Elsevier Science Sa, 2019) Tas, Mahmut; Altin, Yasin; Bedeloğlu, AyşeIn this study, an environmental and economical multi-step reduction method has been developed for the reduction of graphene oxide thin films more efficiently. Within the scope of the method, the graphene oxide films produced were subjected to the process of chemical reduction with L-ascorbic acid (Vitamin C) as the first step and then to the process of thermal reduction that can be performed through progressive thermal annealing without any need for special atmospheric conditions as the second step. In addition, the impact of L-ascorbic acid solutions with different molarities (5, 25, 50, 100, 200, 400 and 800 mM) on the conductivity of the reduced graphene oxide produced was examined and compared with hydrazine hydrate for the same concentrations. Besides, the impact of different thermal annealing temperatures (70 degrees C, 120 degrees C and 300 degrees C) and the process of intermediate drying on the conductivity of the reduced graphene oxide thin films were investigated. The results show that the graphene oxide thin films were best reduced through 800 mM L-ascorbic acid and progressive thermal annealing combination (at 70 degrees C, 120 degrees C and 300 degrees C respectively) and that 13.2 k Omega/sq. surface resistivity was achieved and that the intermediate heating at 120 degrees C made at least 10% positive contribution to this.Öğe Solution-processed transparent conducting electrodes with graphene, silver nanowires and PEDOT:PSS as alternative to ITO(Elsevier Science Sa, 2016) Altin, Yasin; Tas, Mahmut; Borazan, Ismail; Demir, Ali; Bedeloğlu, AyşeNovel transparent electrodes, including graphene, silver nanowires (AgNWs) and poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) serving as the low-cost and flexible alternative to indium tin oxide (ITO) are of interest to the organic electronic industry in recent years. In this paper, transparent, flexible and conductive nanocomposite electrodes were fabricated by using different combinations of graphene, AgNWs, PEDOT:PSS materials via spin coating technique. Optical, morphological and electrical properties of solution-processed electrodes were characterized. Transparent conductive electrode (TCE) based on PEDOT:PSS/AgNW/graphene construction exhibited 216.67 Omega/sq sheet resistance with-83% transparency. Additionally, after 100 cycles of bending, the sheet resistance of PEDOT:PSS/AgNW/graphene electrode on the flexible polyethylene terephthalate (PET) substrate was found to be about 223 Omega/sq, while conventional ITO-coated PET substrate exhibited 83,050 Omega/sq resistance, which was about 400 times more than that of resistance before bending. Optical and electrical measurements showed that obtained nanocomposite electrodes may be promising alternatives to ITO to be used in flexible optoelectronic devices. (C) 2016 Elsevier B.V. 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