Yazar "Zafer, C." seçeneğine göre listele
Listeleniyor 1 - 9 / 9
Sayfa Başına Sonuç
Sıralama seçenekleri
Öğe Analyzing of DSSCs Fabricated by Nb:TiO2 Characterized and Synthesized with Sol-Gel in the Magnetic Field(Springer, 2019) Kutlu, N.; Zafer, C.; Ozek, N.The charge transfer and photovoltaic performance of dye-sensitized solar cells (DSSCs) can be improved by increasing the conductivity of photoanodes used in their fabrication. To increase the conductivity of the photoanode, Nb transition metal was doped into a titanium dioxide (TiO2) crystal lattice by using two different precursors, such as NbCl5 and Nb(OEt)(5). Nb doped TiO2 (Nb:TiO2) and mesoporous (mp)-TiO2 nanomaterials were synthesized via the sol-gel method by mixing crosswise effectively with two magnets in different two beakers for 24 h. DSSCs were fabricated by using mp-TiO2 and Nb:TiO2 photoanodes sensitized with Z907 dye. The scanning electron microscopy (SEM) images unknown in scientific literature are getting darker with the decreased of the surface porosity and, while they are getting brighter with the increased the surface porosity. The ultraviolet-visible (UV-Vis) graphs of photoanodes showed the Burstein-Moss (B-M) effect occurred by optic band gap energy (E-OBG) enlarged due to high Nb doping level. Moreover, this effect, especially in the UV region of the electromagnetic spectrum, was seen in IPCE spectra of DSSCs due to the electronic band gap of TiO2 tailored and split via Nb doping by mixing crosswise effectively with magnets, too. The dark current (I-DC) of DSSCs decreased with Nb doped in the TiO2 lattice. The highest short circuit current (I-sc) values of DSSCs were observed for optimum Nb doping levels. The recombination resistance (Z(2)') at TiO2/dye/electrolyte interface of DSSCs increased with increasing Nb doping level. As a result, it was seen as a good correlation between E-OBG, Z(2)' and I-sc values that changed with Nb doping level.Öğe Atomic-scale understanding of dichlorobenzene-assisted poly 3-hexylthiophene-2,5-diyl nanowire formation mechanism(Elsevier Science Bv, 2017) Yagmurcukardes, M.; Kiymaz, D.; Zafer, C.; Senger, R. T.; Sahin, H.Low-dimensional Poly 3-hexylthiophene-2,5-diyl (P3HT) structures that serve efficient exciton dissociation in organic solar cells, play a major role in increasing the charge collection, and hence, the efficiency of organic devices. In this study, we theoretically and experimentally investigate the Dichlorobenzene (DCB)-assisted formation of P3HT nanowires. Our experiments show that the solution of DCB molecules drive randomly oriented P3HT polymers to form well-stacked nanowires by stabilizing tail-tail and pi-pi interactions. Here the question is how DCB molecules migrate into the P3HT layers while forming the nanowire structure. Our density functional theory-based calculations reveal that the vertical migration of the DCB molecules between P3HT layers is forbidden due to a high energy barrier that stems from strong alkyl chain-DCB interaction. In contrast to vertical diffusion, lateral diffusion of DCB molecules in between P3HT layers is much more likely. Our results show that migration of a DCB molecule occurs through the alkyl groups with a low energy barrier. Therefore, laterally diffused DCB molecules assist nucleation of top-to-top stacking of P3HT polymers and formation of well-ordered nanowires. (C) 2017 Elsevier B.V. All rights reserved.Öğe Conformational control of morphology for perylene diimide dimer as electron transporting material at perovskite surface(Elsevier B.V., 2023) Ötken, A.A.; Saltan, G.M.; Yeşil, T.; Zafer, C.; Dinçalp, H.Synthesis of core-twisted perylene diimide (PDI) dimers attached with thiophene linkers (PDI-NHR-Th(1–4)) and their electron transporting ability at perovskite surface were studied. Synthesized dyes showed a high-lying lowest unoccupied molecular orbital (LUMO) energy levels between –3.68 and –3.71 eV, which were compatible with the conduction band of CH3NH3PbI2Br (–3.60 eV). Herein, we have investigated the role of the different substituted positions of PDI monomers to thiophene linkage from its (2,5)-, (3,4)-, (2,4)-, or (2,3)-positions in modulating the morphology of PDI dimer, aggregation behavior for charge transfer properties, optical shifts in ground and excited states, and recombination resistances at the interfaces of p-i-n devices. Conformational changes of PDI dimers attaching to different positions of thiophene linkers are found to affect not only photopysical dynamics of excited states of the dyes, but also charge transport kinetics at the perovskite interfaces, changing the photovoltaic performance. © 2023 Elsevier B.V.Öğe Controlled growth mechanism of poly (3-hexylthiophene) nanowires(Iop Publishing Ltd, 2016) Kiymaz, D.; Yagmurcukardes, M.; Tomak, A.; Sahin, H.; Senger, R. T.; Peeters, F. M.; Zareie, H. M.; Zafer, C.Synthesis of 1D-polymer nanowires by a self-assembly method using marginal solvents is an attractive technique. While the formation mechanism is poorly understood, this method is essential in order to control the growth of nanowires. Here we visualized the time-dependent assembly of poly (3-hexyl-thiophene-2,5-diyl) (P3HT) nanowires by atomic force microscopy and scanning tunneling microscopy. The assembly of P3HT nanowires was carried out at room temperature by mixing cyclohexanone (CHN), as a poor solvent, with polymer solution in 1,2-dichlorobenzene (DCB). Both pi-pi stacking and planarization, obtained at the mix volume ratio of P3HT (in DCB):CHN (10:7), were considered during the investigation. We find that the length of nanowires was determined by the ordering of polymers in the polymer repetition direction. Additionally, our density functional theory calculations revealed that the presence of DCB and CHN molecules that stabilize the structural distortions due to tail group of polymers was essential for the core-wire formation.Öğe Experimental Analysis of the Potential Induced Degradation Effect on Organic Solar Cells(Hindawi Ltd, 2017) Akcaoglu, S. C.; Martinopoulos, G.; Zafer, C.Renewable energy applications are increasing daily, and solar electricity, in the form of photovoltaics, is getting more and more important worldwide. As photovoltaics are connected both in series and in parallel, the panels are exposed to high potentials compared to the ground; thus, high voltage stress (HVS) occurs. The scope of this paper is to analyze experimentally the potential induced degradation (PID) in organic solar cells. To that end, organic solar cells are manufactured and are then undergone a series of voltage-dependent degradation and time-dependent voltage degradation tests. In addition to that, they are also exposed to gaseous oxygen, oxygen plasma, air degradation, and annealing, and the degradation effects are compared with PID results. From the analysis, it is apparent that annealing, air, gaseous oxygen, and oxygen plasma degradation have similar effects with PID, while due to simple diode characteristics, organic cells proved to be relatively durable to potential induced degradation. At low voltages (10 V), the organic cells withstood degradation adequately, with a drop of 23% in their initial efficiency. As voltage increased, the degradation rate increased considerably reaching a 93% efficiency drop when 30 V was applied for 20 minutes.Öğe Investigation of cell-level potential-induced degradation mechanisms on perovskite, dye-sensitized and organic photovoltaics(Pergamon-Elsevier Science Ltd, 2019) Akcaoglu, S. C.; Martinopoulos, G.; Koidis, C.; Kiymaz, D.; Zafer, C.The study focuses on the effect of bias voltage degradation or Potential Induced Degradation (PID) on the efficiency of perovskite (PSCs), dye-sensitized (DSSCs) and organic (OPVs) solar cells. For the PID study, voltage depended and time-depended degradation tests have been carried out at solar cell level; the cells were fabricated and tested in the same conditions. Furthermore, the solar cells were exposed to both, annealing and cooling tests in order tp highlight the various PID characteristics. Thus, the mechanisms induced during the PID degradation were thoroughly investigated. Results revealed that DSSCs are far more vulnerable to voltage degradation than other solar cell technologies. the current work illustrates that OPV solar cells can be considered as voltage durable compared to PSCs and DSSCs ones. OPV solar cells lost 23% of their initial efficiency whereas PSC and DSSC cells were entirely degraded after the application of 5.5 V and 2.5 V voltage respectively. Furthermore, in contrast to OPV, DSSCs and PSCs did not exhibit charging effect when a 5 V voltage was applied.Öğe Soluble derivatives of perylene and naphthalene diimide for n-channel organic field-effect transistors(Elsevier Science Bv, 2006) Singh, Th. B.; Erten, S.; Guenes, S.; Zafer, C.; Turkmen, G.; Kuban, B.; Teoman, Y.; Sariciftci, N. S.; Icli, S.Solution-processed n-type organic field-effect transistors (OFETs) have been fabricated using soluble derivatives of perylene diimide and naphthalene diimide. We report the synthesis of the organic semiconductors and the fabrication of bottom gate OFET devices using solution-processed organic dielectrics. Surface morphology studies reveal films with layered textures and liquid crystalline-like structure. Devices show field-effect electron mobilities of 10(-2) cm(2)/V s and 10(-3) cm(2)/V s for N,N'-bis-n-butyl-1,4,5,8-naphthalenediimide-NDI under inert conditions and in air, respectively. N,N'-bis-(1-pentyl)hexyl-3,4,9,10-perylene diimide-PDI-4 shows mobility of 5 x 10(-4) cm(2)/V s. Organic field-effect transistors based on N,N'-bis(dehydroabietyl)-3,4,9,10-perylene diimide-PDI-1 derivative exhibit ambipolar transport. (c) 2006 Elsevier B.V. All rights reserved.Öğe Spectrophotochemical and electrochemical characterization of perylene derivatives adsorbed on nanoporous metaloxide films(Edp Sciences S A, 2007) Kus, M.; Demic, S.; Zafer, C.; Saygili, G.; Bilgili, H.; Icli, S.Electrochemistry of perylene imide and anhydride derivatives adsorbed on semiconductor TiO2 (NT) and insulator Al2O3 (NA) metal oxide films were presented. Adsorption rates on metal oxide surface are observed to be strongly depending on molecular structure. Monoanhydride-monoimide derivatives show two reversible reductions in solution and one reversible reduction in films. Color change from red to blue and violet is observed indicating the formation of monoanion and dianion radicals. Spectroelectrochemical measurements support this interpretation. The color reversal is quite stable in NA films in comparison with NT films.Öğe Thieno[3,2-b]thiophene and triphenylamine-based hole transport materials for perovskite solar cells(Frontiers Media S.A., 2023) Isci, R.; Unal, M.; Yesil, T.; Ekici, A.; Sütay, B.; Zafer, C.; Ozturk, T.Heterocyclic compounds have played significant roles in achieving high performance as hole transport materials (HTMs) for perovskite solar cell (PSC) applications. Various studies have focused on the development of fused heterocyclic conjugated structures for hole transport materials. In this report, three novel ?-extended conjugated materials (M1-M3), based on thieno[3,2-b]thiophene (TT) and 4,4?-dimethoxytriphenylamine [TPA(OMe)2], were designed and successfully synthesized via Palladium (0) catalyzed Suzuki coupling reaction. Their optical, electrochemical, and thermal properties were investigated by UV-Vis, fluorescence, cyclic voltammetry, and thermal analysis. The materials were utilized as hole transport materials in p-i-n architecture perovskite solar cells, which displayed performances of open-circuit voltage (Voc) as high as 1,050 mV, a maximum short-circuit current (Jsc) of 16,9 mA/cm2, a maximum fill factor (FF) of 29.3%, and a power conversion efficiency (PCE) of 5.20%. This work demonstrated that thieno[3,2-b]thiophene and TPA(OMe)2-based structures are promising cores for high-performance hole transport materials in perovskite solar cell architecture. Copyright © 2023 Isci, Unal, Yesil, Ekici, Sütay, Zafer and Ozturk.
