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    A Facile Approach to Produce Activated Carbon from Waste Textiles via Self-Purging Microwave Pyrolysis and FeCl3 Activation for Electromagnetic Shielding Applications
    (Mdpi, 2024) Sert, Sema; Gultekin, Sirin Siyahjani; Gultekin, Burak; Kaya, Deniz Duran; Korlu, Aysegul
    This study aims to convert composite textile structures composed of nonwoven and woven fabrics produced from cotton-jute wastes into activated carbon textile structures and investigate the possibilities of using them for electromagnetic shielding applications. To this end, the novel contribution of this study is that it shows that directly carbonized nonwoven textile via self-purging microwave pyrolysis can provide Electromagnetic Interference (EMI) shielding without any processing, including cleaning. Textile carbonization is generally achieved with conventional heating methods, using inert gas and long processing times. In the present study, nonwoven fabric from cotton-jute waste was converted into an activated carbon textile structure in a shorter time via microwaves without inert gas. Due to its polar structure, FeCl3 has been used as a microwave absorbent, providing homogeneous heating in the microwave and acting as an activating agent to serve dual purposes in the carbonization process. The maximum surface area (789.9 m(2)/g) was obtained for 5% FeCl3. The carbonized composite textile structure has a maximum of 39.4 dB at 1 GHz of EMI shielding effectiveness for 10% FeCl3, which corresponds to an excellent grade for general use and a moderate grade for professional use, exceeding the acceptable range for industrial and commercial applications of 20 dB, according to FTTS-FA-003.
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    A narrow range multielectrochromism from 2,5-di-(2-thienyl)-1H-pyrrole polymer bearing pendant perylenediimide moiety
    (Elsevier Sci Ltd, 2015) Sefer, Emre; Bilgili, Hakan; Gultekin, Burak; Tonga, Murat; Koyuncu, Sermet
    A new 2,5-di-(2-thienyl)-1H-pyrrole (SNS) moiety containing perylenediimide (PDI) acceptor as pendant side chain has been synthesized for an electroactive monomer and then directly deposited onto ITO/glass surface via electrochemical polymerization process. The observed electronic interaction only at the excited state due to the presence of phenylene spacer between SNS-donor and PDI-acceptor moiety leads to efficient fluorescence quenching. This charge separation behavior was also proved by theoretical DFT calculations. Thin films of the polymer electropolymerized onto transparent electrode exhibited ambipolar multi-electrochromic behavior including purple, violet-red-khaki-blue colors in both anodic and cathodic regime only between -1.2 and 1.0 V. We further demonstrated that this polymer film has a high contrast ratio (Delta T = 45% at 900 nm), a faster response (0.5 s), high coloration efficiency (254 cm(2) C-1) and retained its performance by 92% even after 5000 cycles. (C) 2014 Elsevier Ltd. All rights reserved.
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    Dopant Free Donor-Acceptor Type Polymer Hole Transport Materials for Efficient and Stable Perovskite Solar Cells
    (Amer Chemical Soc, 2024) Akin Kara, Duygu; Turgut, Sevdiye Basak; Cirak, Dilek; Karaman, Merve; Can, Mustafa; Koyuncu, Sermet; Gultekin, Burak
    A new donor-acceptor type polymers containing benzothiadiazole (HB1) and benzoselenidiazole (HB2) as acceptor units were prepared or use as hole transport layers in perovskite solar cells (PSCs). It was observed that the electrochemical HOMO-LUMO band gap narrowed from 2.74 to 1.88 depending on the variation in the acceptor unit. In addition, the charge-transfer band at 580 nm undergoes a 30 nm red-shift and broadens to the near-infrared region. HB1 and HB2 were introduced as dopant-free HTMs to replace the commonly used 2,2 ',7,7 '-tetrakis[N,N-di(4-methoxyphenyl)amino]-9-9 '-spirobifluorene (spiro-OMeTAD) in planar heterojunction n-i-p type of PSCs. Compared with HB2, HB1 exhibited better film morphology and mobility, resulting in improved charge-carrier extraction and transport. Dopant-free HB1 devices fabricated using the Cs0.05FA0.79MA0.16-Pb (IxBr1-x)3 triple cation perovskite displayed a champion power conversion efficiency of 11.69% under one sun illumination (100 mW cm(-2)) which is higher than the efficiency of HB2-based devices. The inflated performance was attributed to the reduced charge recombination and improved conductivity. In addition, these new HTMs exhibited higher hydrophobicity and thermal stability than their doped spiro-OMeTAD counterpart, making it possible to achieve good stability.
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    Electrochemical and optical properties of biphenyl bridged-dicarbazole oligomer films: Electropolymerization and electrochromism
    (Pergamon-Elsevier Science Ltd, 2009) Koyuncu, Sermet; Gultekin, Burak; Zafer, Ceylan; Bilgili, Hakan; Can, Mustafa; Demic, Serafettin; Kaya, İsmet
    4,4'-Di(N-carbazoyl)biphenyl monomer (CBP) was synthesized and coated onto ITO-glass surface by electrochemical oxidative polymerization. Its CV shows two distinct one-electron and stepwise oxidation processes occurred at 1.29 and 1.61 V. By using this property, the monomer was electrochemically polymerized separately at these oxidation states and thus, two different oligomer films were obtained afterwards. Their spectro-electrochemical and electrochromic properties were also investigated. Switching ability of the oligomers was evaluated by kinetic studies upon measuring the percent transmittance (%T) at their maximum contrast point, indicating that these oligomers were found to be suitable material for electrochromic devices. (C) 2009 Elsevier Ltd. All rights reserved.
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    Push-pull type material having spirobifluorene as ?-spacer for dye sensitized solar cells
    (Pergamon-Elsevier Science Ltd, 2016) Can, Mustafa; Bilgili, Hakan; Demirak, Kadir; Gultekin, Burak; Koyuncu, Sermet; Kus, Mahmut; Zafer, Ceylan
    Two organic dyes for dye-sensitized solar cells (DSSC) based on spirobifluorene were synthesized and characterized. Electrochemical, spectroscopic and photovoltaic properties of the dyes have been investigated. Hexyloxy substituted triarylamine was used as electron donating moiety in the molecule while spirobifluorene and cyanoacrylic acid were used as pi-bridge and acceptor groups, respectively. MK162-sensitized solar cells exhibited a short-circuit current (I-SC) of 4,92 mA cm(-2), an open-circuit voltage (V-OC) of 520 mV and a fill factor (FF) of 0.59, resulting an overall power conversion efficiency of 1,52 where the reference cell, Z907 was yielded an overall conversion efficiency of 4.08% efficiency with 620 mV of V-OC and 14.51 mA cm(-2) of Isc under standard AM 1.5 illumination. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
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    Quantification of the Effects of Recombination and Injection in the Performance of Dye-Sensitized Solar Cells Based on N-Substituted Carbazole Dyes
    (Amer Chemical Soc, 2010) Barea, Eva M.; Zafer, Ceylan; Gultekin, Burak; Aydin, Banu; Koyuncu, Sermet; Icli, Siddik; Fabregat Santiago, Francisco
    Two new sensitizers for dye sensitized solar cells have been designed consisting of thiophene units asymmetrically functionalized by N-aryl carbazole. The di(tert-butyl) carbazole moieties acts as an electron donor group, the thiophene chain as a bridge group, and the cyanoacrylic acid as an anchoring and electron acceptor group. An increase of the conjugation length produces two main effects: first, it leads to a red-shift of the optical absorption of the dyes, resulting in an improved overlap of the absorption with the solar spectrum. Second, the oxidation potential decreases. The photovoltaic performance of this set of dyes as sensitizers in mesoporous TiO2 solar cells was investigated using electrolytes containing the iodide/triiodide redox couple. The dye with the best absorption characteristics showed the highest photocurrent but lower open circuit voltage due to more losses by recombination. A trend between structure (molecule dyes size) and recombination is demostrated using an analysis procedure based on beta-recombination model that combines impedance spectroscopy and density current-voltage data.
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    Stable Efficient Solid-State Supercapacitors and Dye-Sensitized Solar Cells Using Ionic Liquid-Doped Solid Biopolymer Electrolyte
    (Amer Chemical Soc, 2024) Konwar, Subhrajit; Siyahjani Gultekin, Sirin; Gultekin, Burak; Kumar, Sushant; Punetha, Vinay Deep; Yahya, Muhd Zu Azhan Bin; Diantoro, Markus
    As synthetic and nonbiodegradable compounds are becoming a great challenge for the environment, developing polymer electrolytes using naturally occurring biodegradable polymers has drawn considerable research interest to replace traditional aqueous electrolytes and synthetic polymer-based polymer electrolytes. This study shows the development of a highly conducting ionic liquid (1-hexyl-3-methylimidazolium iodide)-doped corn starch-based polymer electrolyte. A simple solution cast method is used to prepare biopolymer-based polymer electrolytes and characterized using different electrical, structural, and photoelectrochemical studies. Prepared polymer electrolytes are optimized based on ionic conductivity, which shows an ionic conductivity as high as 1.90 x 10(-3) S/cm. Fourier transform infrared spectroscopy (FTIR) confirms the complexation and composite nature, while X-ray diffraction (XRD) and polarized optical microscopy (POM) affirm the reduction of crystallinity in biopolymer electrolytes after doping with ionic liquid (IL). Thermal and photoelectrochemical studies further affirm that synthesized material is well stable above 200 degrees C and shows a wide electrochemical window of 3.91 V. The ionic transference number measurement (t ion) confirms the predominance of ionic charge carriers in the present system. An electric double-layer capacitor (EDLC) and a dye-sensitized solar cell (DSSC) were fabricated by using the highest conducting corn starch polymer electrolyte. The fabricated EDLC and DSSC delivered an average specific capacitance of 130 F/g and an efficiency of 1.73% in one sun condition, respectively.