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dc.contributor.advisorDağ, Ömer
dc.contributor.authorYılmaz, Ezgi
dc.date.accessioned2016-04-28T12:34:37Z
dc.date.available2016-04-28T12:34:37Z
dc.date.copyright2015-09
dc.date.issued2015-09
dc.date.submitted02-09-2015
dc.identifier.urihttp://hdl.handle.net/11693/29010
dc.descriptionCataloged from PDF version of thesis.en_US
dc.descriptionIncludes bibliographical references (leaves 93-103).en_US
dc.descriptionThesis (M.S.): Bilkent University, Department of Chemistry, İhsan Doğramacı Bilkent University, 2015.en_US
dc.description.abstractLiquid crystals are one of the most widely studied and used materials in chemistry. The properties of liquid crystals make them interesting to research also for various electrochemical applications. In this context, lithium salts such as LiI, LiCl, LiBr, and LiNO3 can be assembled using non-ionic surfactants into lyotropic liquid crystalline (LLC) mesophases[1], [2] and used as gel electrolytes in various applications. In this work, the LLC mesophases of LiI with and without other lithium salts (such as LiCl, LiBr, and LiNO3) were prepared using 10-lauryl ether (C12H25(CH2CH2O)10OH, denoted as C12EO10) and characterized using the FT-IR (Fourier Transform Infrared Spectroscopy), Raman spectroscopy, XRD (X-Ray Diffraction), POM (Polarized Optical Microscopy), and AC conductivity measurements. Beside from single salt-surfactant mesophases, we also prepared LiI/I2 redox couple in an LLC phase with the help of a non-ionic surfactant and they were also characterized using the same techniques. We found out that the mesophases can be prepared as gels by directly mixing salt and surfactant with certain amounts of water or as solutions using excess solvent (such as water, ethanol, or acetonitrile) that can be evaporated to form the LLC mesophases. The water content of both sets of samples is the same upon exposing to the atmosphere for a certain time and it only depends on the salt amount and humidity under the ambient conditions (around room temperature and 20-25 % RH). The required water/salt ratio for a stable mesophase is around 3.0 which, it is much lower than the water needed to dissolve those salts in an aqueous media. The water/salt mole ratio closely follows the Hofmeister series of anions, where the water amount order is as follows; LiCl>LiBr>LiI>LiNO3, however, the AC ionic conductivity follows a different order; LiNO3>LiCl>LiBr>LiI. Adding I2 by 1/10 mole ratio of the LiI into the media does not change the properties of the mesophases. The AC conductivity increases with increasing salt and water content of the mesophases with a typical conductivity of around 0.1 to 1.0 mS/cm-1. The mesophases are also stable in a very broad temperature (below 0 °C to 60-130 °C) and salt concentration (2-10 salt/surfactant mole ratio) ranges. Finally, the LiI/I2 mesophases were used as gel-electrolytes in dye sensitized solar cells (DSSCs) as gel-electrolytes and redox couples. A set of samples were prepared with different ratios of the LiI:I2 redox couple (such as, 1:0.1, 1:0.2, 2:0.2, 2:0.3, 3:0.2, 3:0.3, 4:0.4, and 5:0.5) and the solar performances were tested in a DSSC, which contains N719 dye sensitized TiO2 anode and Pt cathode using a solar simulator. However, the LLC phases have gel like structure and it is hard to infiltrate the gel into the pores of dye modified nano-TiO2 films. To overcome the diffusion problem, the gel-electrolytes were also prepared as a solution in excess water, ethanol or acetonitrile that evaporates upon infiltration over time. In addition to this, by changing the procedure of preparing the TiO2 paste, improvement on results was also obtained. The DSSC provides 0.2 % efficiencies with 0.50 fill factors when gel-electrolytes are used. Since water is used for preparing the LLC phases, we had always lower Voc values. However, when it is prepared as a solution with excess ethanol, it provides up to 3.33 % efficiencies with 9.58 mA/cm2 short circuit current and 0.6 V open circuit voltage. Also, new procedure for preparing the TiO2 paste provides us even higher Voc values such as 0.76 V, which is unusual for the water based LLC electrolytes in this area.en_US
dc.description.statementofresponsibilityby Ezgi Yılmaz.en_US
dc.format.extentxix, 103 leaves : charts, plates.en_US
dc.language.isoEnglishen_US
dc.rightsinfo:eu-repo/semantics/openAccessen_US
dc.subjectLyotropic liquid crystalen_US
dc.subjectMesophaseen_US
dc.subjectSolar cellen_US
dc.subjectGel electrolyteen_US
dc.subjectRedox coupleen_US
dc.subjectLithium saltsen_US
dc.titleInvestigation of lithium salts-nonionic surfactant lyotropic liquid crystalline mesophases in a dye sensitized solar cell as gel electrolyteen_US
dc.title.alternativeLityum tuzları ve iyonik olmayan yüzeyaktif liyotropik sıvı kristal fazların boya duyarlı güneş hücrelerinde jel elektrolit olarak kullanılmasıen_US
dc.typeThesisen_US
dc.departmentDepartment of Chemistryen_US
dc.publisherBilkent Universityen_US
dc.description.degreeM.S.en_US
dc.identifier.itemidB151170
dc.embargo.release2017-01-01


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