Yazar "Toppare, Levent Kamil" seçeneğine göre listele

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    A triazoloquinoxaline and benzodithiophene bearing low band gap copolymer for electrochromic and organic photovoltaic applications
    (Elsevier Ltd, 2017) Özdemir Hacıoğlu, Şerife; Akbaşoğlu Ünlü, Naime; Aktaş, Ece; Hizalan, Gönül; Yıldız, Dilber Esra; Çırpan, Ali; Toppare, Levent Kamil
    A new triazoloquinoxaline and benzodithiophene based copolymer was synthesized to investigate its electrochemical, optical and photovoltaic behaviors. According to the polymer design, combination of two acceptor units (benzotriazole and quinoxaline) which contribute imine bonds to the structure and a triazoloquinoxaline unit for enhancing electron accepting ability was pursued. As a result of electrochemical studies, the copolymer PTQBDT has a low lying HOMO energy level as ?5.23 eV which increases the chemical stability of the resulting polymer and leads to a higher Voc. In addition, the copolymer has an ambipolar character with two well-defined redox couples in the n-doped state and multichromic behavior. In the context of optical studies, PTQBDT has wide absorption range in the visible region with a tail in the NIR region, which yields a low band gap of 1.20 eV. Organic photovoltaic devices were designed using PTQBDT (the electron donor) and PC71BM (the electron acceptor) for the preliminary studies. The resulting device exhibits a power conversion efficiency of 2.0% with a current density of 8.07 mA cm?2, an open-circuit voltage of 0.45 V, and a fill factor of 55%. The carrier mobility of the PTQBDT was calculated as 3.00 × 10?3 cm2 V?1 s?1 via space-charge-limited current (SCLC) method.
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    Benzodithiophene and benzotriazole bearing conjugated polymers for electrochromic and organic solar cell applications
    (Electrochemical Society Inc., 2017) Akbaşoğlu Ünlü, Naime; Hacıoğlu, Şerife O.; Hizalan, Gönül; Yıldız, Dilber Esra; Toppare, Levent Kamil; Çırpan, Ali
    Herein, alternating donor-acceptor type benzodithiophene and benzotriazole bearing copolymers were synthesized and thieno[3,2-b]thiophene and furan units were incorporated as ?-bridges. The application of these polymers for electrochromic and photovoltaic studies were performed. Spectroelectrochemical studies illustrate that both polymers showed multichromic behavior due to tailoring of polaron bands in visible region. Photovoltaic properties of P2 were performed by conventional device structure. The best performance device based on P2: PC71BM (1:3, w/w) exhibited the power conversion efficiency of 2.98%, with Voc of 0.74 V, Jsc of 6.31 mA/cm2, and FF of 64%. The carrier mobility of the P2: PC71BM was calculated as 1.37 × 10?3 cm2/V.s via space-charge-limited current method. © 2017 The Electrochemical Society. All rights reserved.
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    Benzotriazole and benzodithiophene containing medium band gap polymer for bulk heterojunction polymer solar cell applications
    (John Wiley and Sons Inc., 2014) Ünay, Hande; Akbaşoğlu Ünlü, Naime; Hizalan, Gönül; Özdemir Hacıoğlu, Şerife; Yıldız, Dilber Esra; Toppare, Levent Kamil; Çırpan, Ali
    An alternating donor?acceptor copolymer based on a benzotriazole and benzodithiophene was synthesized and selenophene was incorporated as ??bridge. The photovoltaic and optical properties of polymer were studied. The copolymer showed medium band gap and dual absorption peaks in UV?Vis absorption spectra. Photovoltaic properties of P?SBTBDT were performed by conventional device structure. The OSC device based on polymer: PC71BM (1:1, w/w) exhibited the best PCE of 3.60% with a Voc of 0.67 V, a Jsc of 8.95 mA/cm2, and a FF of 60%. This finding was supported with morphological data and space charge limited current (SCLC) mobilities. The hole mobility of the copolymer was estimated through SCLC model. Although surface roughness of the active layer is really high, mobility of a polymer was found as 7.46 × 10?3 cm2/Vs for optimized device that can be attributed to Se?Se interactions due to the larger, more?polarizable Se atom.
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    Benzotriazole and benzothiadiazole containing conjugated copolymers for organic solar cell applications
    (Elsevier Ltd, 2012) Karakuş, Melike; Apaydın, Doğukan Hazar; Yıldız, Dilber Esra; Toppare, Levent Kamil; Çırpan, Ali
    2-Dodecyl benzotriazole (BTz) and benzothiadiazole (BTd) containing copolymers poly(4-(2-dodecyl-2H-benzo[d][1,2,3]triazol-4-yl)benzo[c][1,2,5] thiadiazole (P1), poly(4-(5-(2-dodecyl-7-(thiophen-2yl)-2H-benzo[d][1,2,3] triazol-4-yl)thiophen-2-yl)benzo[c][1,2,5] thiadiazole (P2) and poly(4-(5-(2-dodecyl-7-(4-hexylthiophen-2-yl)-2H-benzo[d] [1,2,3]triazol-4-yl)- 3-hexylthiophen-2-yl) benzo[c][1,2,5] thiadiazole (P3) were synthesized via Suzuki polycondensation. We report the application of conjugated copolymers in bulk heterojunction photovoltaic devices. When the copolymers were blended with [6,6]phenyl-C61-butyric acid methyl ester (PCBM), P2 showed the best performance with an open circuit voltage (Voc), a short-circuit current density (Jsc) and a power conversion efficiency (PCE) of 0.45 V, 3.48 mA cm-2 and 0.45%, respectively, under AM 1.5G illumination conditions (100 mW cm-2). The hole mobilities of the devices were calculated from J-V curves using Space Charge Limited Current (SCLC) method and the maximum mobility value was found to be 3.15 × 10-5 cm 2 V-1 s-1 for the P2:PCBM blend. © 2012 Published by Elsevier Ltd.
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    Dielectric and electrical properties of an organic device containing benzotriazole and fluorene bearing copolymer
    (2013) Yıldız, Dilber Esra; Apaydın, Doğukan Hazar; Toppare, Levent Kamil; Çırpan, Ali
    Dielectric and electrical properties of a benzotriazole and fluorene copolymer were investigated using current-voltage (I-V), capacitance-voltage (C-V), and conductance-voltage (G/w-V) measurements at room temperature. The electrical parameters, barrier height (?Bo), and ideality factor (n) obtained from the forward bias LnI-V plot were found as 0.453 eV and 2.08, respectively. The Rs values were found as 2.20, 2.12, 1.90 ? using dV/dLnI versus I, H(I) versus I and F(V)-V plots, respectively. The dielectric constant (??), the dielectric loss (??), and the ac electrical conductivity (?ac) are a strong function of voltage and frequency. Decrease in ?? and ?? values with increasing frequency was observed. On the other hand, the increase of ?ac with increasing frequency was observed. Experimental results show that the conjugated copolymer plays an important role in the values of barrier height, ideality factor, series resistance, and dielectric parameters. © 2012 Wiley Periodicals, Inc.
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    Effect of layer thickness on the electrical parameters and conduction mechanisms of conjugated polymer-based heterojunction diode
    (John Wiley and Sons Inc., 2017) Yıldız, Dilber Esra; Apaydın, Doğukan Hazar; Toppare, Levent Kamil; Çırpan, Ali
    In this study, thickness-dependent current density–voltage (J–V) characteristics obtained for poly{(9,9-dioctylfluorene)?2,7-diyl-(4,7-bis(thien-2-yl) 2-dodecyl-benzo[1,2,3] triazole)} (PFTBT) conjugated copolymer based heterojunction diode fabricated on ITO were investigated in terms of electrical characteristics. In order to analyze J–V plots with ITO/PEDOT:PSS/PFTBT:PC61BM/LiF/Al configuration, the thickness-dependent J–V measurements were applied in the thickness range between 90 and 200 nm. The effect of PFTBT:PC61BM layer thickness on the forward J–V characteristics were investigated by evaluating electrical parameters such as zero bias barrier height (?Bo), ideality factor (n), shunt resistance (Rsh), series resistance (Rs), the interface states density (Nss), and space-charge limited mobility. The results show that at PFTBT:PC61BM layer thickness of 90 and 200 nm, ideality factor for ITO/PEDOT:PSS/PFTBT:PC61BM/LiF/Al heterojunction diodes ranged from 2.726 to 3.121 and the thermionic emission over the heterojunction diodes is crucial at low current densities and the intrinsic thermally generated charge carriers controlled the forward current this region of the heterojunction diode. At relatively higher voltage, the current mechanism of ITO/PFTBT:PC61BM/PEDOT:PSS/LiF/Al heterojunction diodes were found to obey a space charge limited (SCLC) conduction mechanism. The values of Nss and Rs in heterojunction diodes increase with increasing PFTBT:PC61BM layer thickness and effect the main electrical parameters of diodes. In addition, the leakage current of heterojunction diodes are taken and interpreted via Poole-Frenkel emission and Schottky emission. The leakage current was controlled in ITO/PEDOT:PSS/PFTBT:PC61BM/LiF/Al heterojunction diodes by Poole-Frenkel emission above 140 nm and by Schottky emission under 140 nm. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44817. © 2017 Wiley Periodicals, Inc.
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    Electrical characteristics of organic heterojunction with an alternating benzotriazole and fluorene containing copolymer
    (Springer, 2020) Güllü, Hasan Hüseyin; Yıldız, Dilber Esra; Toppare, Levent Kamil; Çırpan, Ali
    The current-voltage (I - V) and capacitance-voltage (C - V) characteristics of the organic heterojunction diode were investigated in a wide temperature range from 80 to 320 K and frequency range from 10 kHz to 1 MHz, respectively. Alternative to the copolymer partner poly(3-hexylthiophene) (P3HT) to [6,6]phenyl-C61-butyric acid methyl ester (PCBM), poly((9,9-dioctylfluorene)-2,7diyl-(4,7-bis(thien-2-yl)-2-dodecyl-benzo[1,2,3]triazole)) (named as copolymer in this work) was adapted to the bulk-heterojunction layer in the organic diode. Together with the use of Lif/Al bilayer electrode, the diode was fabricated as in the form of Al/LiF/copolymer:PCBM/PEDOT:PSS/ITO/glass. Under the applied bias voltage, this organic-based diode shows two- orders of magnitude rectifying behavior. According to thermionic emission (TE) model, the diode parameters such as saturation current, barrier height and ideality factor were determined and parasitic resistances were also extracted from the conventional ohmic relation. As to the temperature dependency of the diode parameters and their response to the temperature variation, barrier inhomogeneity, surface state and series resistance effects were found in dominant behavior on the current flow. The conduction mechanism was modeled by assuming low-barrier patches around the main barrier that supports TE at low temperatures and their distribution was expressed by a Gaussian function. In addition, series resistance values were detailed depending on temperature using Cheung's model. C - V analysis was performed to evaluate the distribution of surface states at the interface as a function of frequency. Based on the C - V plots, the effects of charges at these traps were observed especially at low frequencies. Additionally, from these results, Fermi level, surface potential and donor concentration values were evaluated in a wide frequency range.
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    Leakage current by Frenkel-Poole emission on benzotriazole and benzothiadiazole based organic devices
    (Elsevier Ltd, 2014) Yıldız, Dilber Esra; Karakuş, Melike; Toppare, Levent Kamil; Çırpan, Ali
    In this study three different organic semiconductors were used in the fabrication of ITO/PEDOT:PSS/Polymer:PCBM/LiF/Al configuration. Reverse current density-voltage (Jr-V) measurements of the samples were investigated to define the reverse-bias leakage current mechanisms on benzotriazole and benzothiadiazole based organic devices. Our results indicate that the Jr-V plot behaviors are given by linear dependence between In (Jr) and V1/2, where Jr is the reverse current density, and V is the applied voltage. This behavior is well known as the Poole-Frenkel (PF) effect where it is found to be dominating in the reverse-bias leakage current.
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    Optimizing the organic solar cell efficiency: Role of the active layer thickness
    (2013) Apaydın, Doğukan Hazar; Yıldız, Dilber Esra; Çırpan, Ali; Toppare, Levent Kamil
    A 2-dodecyl benzotriazole and 9,9-dioctylfluorene containing alternating conjugated polymer, poly((9,9-dioctylfluorene)-2,7-diyl-(4,7-bis(thien-2-yl) 2-dodecyl-benzo[1,2,3]triazole)) (PFTBT), was blended with PCBM (1:1, w/w) and spin coated on ITO substrates using varying rotational speeds to obtain different active layer thicknesses. J–V characteristics of the constructed devices were investigated both in dark and under simulated sunlight (AM 1.5G, 100 mW/cm2). For the determination of hole mobilities the space charge limited current (SCLC) method was used and found as 1.69×10?6 cm2/Vs. In addition, the power conversion efficiency (PCE) of the devices was varied according to active layer thickness and the best power conversion efficiency was recorded as 1.06%. Moreover, incident-photon-to-current-efficiency (IPCE) measurements were carried out and the best efficiency was found to be 51%. Morphology of the active layers was probed using AFM and TEM techniques.
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    Silafluorene-based polymers for electrochromic and polymer solar cell applications
    (John Wiley and Sons Inc., 2015) Erlik, Ozan; Akbaşoğlu Ünlü, Naime; Hizalan, Gönül; Özdemir Hacıoğlu, Şerife; Çömez, Seda; Yıldız, Dilber Esra; Toppare, Levent Kamil; Çırpan, Ali
    In this study, four novel silafluorene (SiF) and benzotriazole (Btz) bearing conjugated polymers are synthesized. In the context of electrochemical and optical studies, these polymers are promising materials both for electrochromic device (ECD) and polymer solar cell (PSC) applications. All of the polymers are ambipolar (both p- and n-dopable) and multichromic. Electrochemistry experiments indicate that incorporation of selenophene instead of thiophene unit increases the HOMO energy level of the polymers. Power conversion efficiency of the PSCs reached 1.75% for PTBTSiF, 1.55% for PSBSSiF, 2.57% for PBTBTSiF, and 1.82% for PBSBSSiF. The hole mobilities of the polymers are estimated through space charge limited current (SCLC) model. PBTBTSiF has the highest hole mobility as 2.44 × 10-3 cm2 V s-1. © 2015 Wiley Periodicals, Inc.
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    Solution processable benzotriazole and fluorene containing copolymers for photovoltaic applications
    (2012) Kaya, Emine; Apaydın, Doğukan Hazar; Yıldız, Dilber Esra; Toppare, Levent Kamil; Çırpan, Ali
    2-Dodecyl benzotriazole and 9,9-dioctylfluorene containing alternating copolymers poly((9,9-dioctylfluorene)-2,7-diyl-(2-dodecyl-benzo[1,2,3]triazole)) (P1), poly((9,9-dioctylfluorene)-2,7-diyl-(4,7-bis(thien-2-yl) 2-dodecyl-benzo[1,2,3]triazole)) (P2), poly((9,9-dioctylfluorene)-2,7-diyl-(4,7- bis(3-hexylthien-5-yl) 2-dodecyl benzo[1,2,3]triazole)) (P3) were synthesized via a typical Suzuki coupling polymerization. UVvis and electrochemical studies indicated that polymers have desirable HOMOLUMO and band gap energy levels, enabling efficient electron transfer when blending them with fullerene derivatives. Photovoltaic properties of the copolymers mixed with [6,6] phenyl-C61-butyric acid methyl ester (PCBM), were investigated. P2 exhibited the best device performance with an open circuit voltage of 0.6 V, short circuit current of 3.4 mA/cm 2 and power conversion efficiency of 0.56% under Air mass 1.5 Global (AM 1.5G, 100 mW/cm 2) illumination. Hole mobilities of the polymers were calculated using space charge limited current (SCLC) method and found to be in the order of 10 -5 for P1 and P2 and 10 -4 for P3. © 2011 Elsevier B.V. All rights reserved.
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    Synthesis of a benzotriazole bearing alternating copolymer for organic photovoltaic applications
    (Royal Society of Chemistry, 2015) İstanbulluoğlu, Çağla; Göker, Seza; Hizalan, Gönül; Özdemir Hacıoğlu, Şerife; Arslan Udum, Yasemin; Yıldız, Dilber Esra; Çırpan, Ali; Toppare, Levent Kamil
    A low band gap donor–acceptor (D–A) copolymer PTBTBDT, namely, poly(2-dodecyl-4,7-di(thiophen-2-yl)-2H-benzo[d][1,2,3]triazole-alt-4,8-bis(2-ethylhexyloxy)benzo[1,2-b:4,5-b?]dithiophene), was designed and synthesized via a Pd-catalyzed Stille polycondensation reaction. The polymer was characterized using 1H NMR spectroscopy, UV-vis absorption spectroscopy, cyclic voltammetry, and gel permeation chromatography (GPC). PTBTBDT has good solubility in common organic solvents, good thermal stability, broad absorption, low band gap and exhibits not only high hole mobility but also moderate photovoltaic properties. PTBTBDT displays broad absorption in the wavelength range from 300 nm to 630 nm, and its HOMO and LUMO energy levels were calculated to be ?4.98 eV and ?3.34 eV, respectively. Bulk heterojunction solar cells were fabricated using PTBTBDT as the electron donor and PC70BM as the acceptor. The device exhibits a power conversion efficiency of 2.12% with a current density of 5.45 mA cm?2, an open-circuit voltage of 0.72 V, and a fill factor of 54% under the illumination of AM 1.5 G, 100 mW cm?2. Under similar device fabrication conditions, the PTBTBDT based device showed considerably improved efficiency among its previously synthesized counterparts, i.e. PBDTDTBTz and PBDTBTz based devices, which have 1.7% and 1.4% efficiencies, respectively. The hole mobility of the PTBTBDT?:?PC70BM (1?:?2 w/w) blend reached up to 1.47 × 10?3 cm2 V?1 s?1 as calculated by the space-charge-limited current (SCLC) method. By side-chain engineering, this study demonstrates a good example of tuning the absorption range, energy level, charge transport, and photovoltaic properties of polymers.