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Öğe 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, SermetA 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.Öğe 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, CeylanTwo 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.Öğe 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, FranciscoTwo 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.Öğe Utilization of biomass-derived activated carbon from Miscanthus for dual energy storage: Enhanced performance in phase change material and supercapacitor applications(Taylor & Francis Inc, 2026) Alptekin, Fikret Muge; Siyahjani-Gultekin, Sirin; Sahin, Damla; Gultekin, Burak; Celiktas, Melih SonerIn this study, bio-derived activated carbons (ACs) obtained from Miscanthus under two distinct synthesis conditions denoted as optimum condition 1 (OC1) and optimum condition 2 (OC2) were systematically investigated for their applicability in dual-mode energy storage. Their performance was assessed in two roles: as supporting materials to enhance the thermal properties of phase change materials, and as electrode materials for electrochemical energy storage systems, such as supercapacitors. This dual evaluation aims to demonstrate the versatility and multifunctionality of Miscanthus-based ACs in both thermal and electrochemical storage platforms. For thermal energy storage, an eutectic blend of stearic acid and palmitic acid (SP) was utilized as the phase change material (PCM), and activated carbon was employed to create shape-stabilized PCM via vacuum impregnation methods, resulting in composite PCMs named SP-OC1 and SP-OC2. SP-OC2 demonstrated a significantly higher encapsulation ratio of 88.95% and an enhanced thermal conductivity of 0.597 Wm-1K-1. It melted at 54.79 degrees C and solidified at 51.89 degrees C, with latent heat values of 133.26 Jg-1 and 135.84 Jg-1, respectively, exhibiting a significant enhancement in thermal conductivity, increasing by up to 117% compared to the eutectic SP. In supercapacitor applications, OC1 cell exhibited superior performance with a capacitance of 131 Fg-1, a power density of 488 Wkg-1, and an energy density of 35.30 Whkg-1, whereas OC2 cell showed a capacitance of 67 Fg-1, a power density of 480 Wkg-1, and an energy density of 15.25 Whkg-1. This difference is ascribed to the matching of ionic liquid ion diameters with the pore sizes of OC1. These results highlight the viability of Miscanthus-derived activated carbons as a cost-effective and sustainable precursor for developing high-performance electrode materials in energy storage systems.
