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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 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 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.