Interligand electron transfer (ILET) may be an essential parameter for the injection ofan electron from the dye into the semiconductor surface of a dye sensitized solar cell(DSSC). Without an efficient injection, competing recombination paths may become apparent. For the future development and design of DSSCs, with the hope of increased energy conversion efficiencies, the ILET dynamics is of great importance. For a long time, the most impressive DSSCs were sensitized with polypyridyl ruthenium dyes for which injection has shown to vary from sub-ps to ns duration. It may therefore be crucial to find means of studying the underlying reasons for the slow injection and in this thesis such an attempt has been made. ILET dynamics has been examined using fs Transient Absorption Anisotropy Spectroscopy in both the IR and Visible. This was done for two ruthenium dye complexes: N712 (cis-diisothiocyanato-bis(2,2’-bipyridyl-4,4’-dicarboxylate)ruthenium(II)) and RuL3 (tris(2,2’-bipyridyl-4,4’-dicarboxylate) ruthenium(II)) which are among the best performing dyes in DSSCs. The initial anisotropy was used to determine whether the excitation is localized on the photoselected ligand or delocalized over the available bipyridyl ligands. The depolarization dynamics of the anisotropy decay showed that the ILET must occur on the sub-ps time scale, resulting in rapid loss of the memory of which ligand was photoselected in the absorption process. This means formation of a metal-to-ligand-charge-transfer state that is randomized over the bipyridyl ligands. These results indicate that ILET dynamics should not limit the injection in DSSCs.

Orientador: Ana Flávia Nogueira / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-24T11:57:50Z (GMT). No. of bitstreams: 1 SantosJunior_GarbasAnacleto_M.pdf: 5163839 bytes, checksum: 6d357533b5e3fc16413a4febf8f9d075 (MD5) Previous issue date: 2014 / Resumo: Neste trabalho são apresentados os resultados da preparação e caracterização de eletrólitos poliméricos usando matriz polimérica de um copolímero derivado de PEO - poli (óxido de etileno-co-2-(2-metoxietoxi) etil glicidil éter) - P(EO-EM) - visando à substituição do par redox, I/I3 , usualmente mais comum em células solares do tipo DSSC, por pares de íons de metais de transição, como Fe e Co . Os eletrólitos foram preparados utilizando razões mássicas fixas de P(EO-EM):GBL de 30-70%. Para os eletrólitos de ferro foram utilizados os sais de FeCl2 + FeCl3·6H2O e para os eletrólitos de cobalto CoCl2 · 6H2O + CoF3. Em ambos os casos foram estudados razões molares entre os cátions de valência II:III de 1:1 e 10:1. Diferentes razões mássicas foram estudadas, sendo estas de 2, 5, 8 e 16% para os eletrólitos de ferro e de 1, 2, 3 e 5% para os eletrólitos de cobalto. Valores máximos de condutividade para os eletrólitos contendo sais de ferro foram de 1,88 x 10 e 1,40 x 10 S cm-1, para concentrações de 16% de sal e razões de 1:1 e 10:1 (Fe:Fe), respectivamente. Enquanto que no caso dos eletrólitos contendo cátions de cobalto foram de 1,41 x 10 e 1,16 x 10 S cm, para concentrações de 5% de sal e razões de 1:1 e 10:1 (Co:Co), respectivamente. Testes de PIA- Photoinduced Absorption Spectroscopy mostraram a eficiência do par redox Fe para regeneração dos corantes L0, N719, D35 e Z907. Entretanto, os mesmos testes mostraram a eficiência do par redox Co para regeneração somente do corante L0. A confecção de dispositivos do tipo DSSC com eletrólitos contendo sais de Fe e Co apresentaram resultados insatisfatórios, possivelmente relacionado com a alta taxa de recombinação do elétron ejetado no TiO2 com os mediadores redox / Abstract: This work presents the results of the preparation and characterization of polymer electrolytes using polymeric matrix of a PEO copolymer-poly (ethylene oxide-co-2-(2-methoxyethoxy) ethyl glycidyl ether) - P (EO-EM) - in order to substitute the redox couple , I-/I3-, usually most common mediators in DSSC solar cells, by transition metal ions pairs, such as Fe and Co . The electrolytes were prepared using fixed P(EO-EM) : GBL weight ratios of 30-70 % . The iron electrolytes were prepared using FeCl2 + FeCl3 o 6H2O salts and CoCl2 o 6H2O + CoF3 were used for the cobalt electrolytes. In both cases, it was studied the molar ratios between cations with valence of II: III of 1:1 to 10:1. Different weight ratios were studied, 2 , 5, 8 and 16% for iron electrolytes and 1 , 2, 3 and 5% for the cobalt electrolytes . Maximum conductivity values for the electrolyte containing iron salts were 1.88 x 10 and 1.40 x 10 S cm at salts concentrations of 16 % and ratios from 1:1 to 10:1 (Fe:Fe), respectively. While in the case of electrolyte containing cobalt cations the conductivity values were 1.41 x 10 and 1.16 x 10 S cm -1 at salts concentrations of 5 % and ratios from 1:1 to 10:1 ( Co:Co), respectively . PIA tests - Photoinduced Absorption Spectroscopy- showed the efficiency of the FeII/III redox couple for the regeneration of L0 , N719 , Z907 and D35 dyes. However, the same tests have shown that the CoI redox couple were only able to regenerate the L0 dye. The DSSC devices with electrolytes containing Fe and Co salts showed unsatisfactory results, possibly related to the high rate of recombination of the electron ejected in TiO2 with the redox mediators / Mestrado / Quimica Inorganica / Mestre em Química

This dissertation has two intersecting foci; firstly, the discovery of a new methodology for the growth of high surface area cuprous oxide (Cu2O) substrates. Secondly, the synthesis and characterization of electron-accepting molecules, and their incorporation into excitonic solar cells (XSCs) using the Cu2O substrates as electrodes. Increasing the surface area of the semiconductor creates more locations for charge transfer to occur thus increasing the overall efficiency of the device. Zinc oxide (ZnO) has been widely studied, and can be easily grown into many different films with high surface area morphologies. The ZnO films serve as sacrificial templates that allow us to electrochemically grow new semiconductors with the same high surface area morphologies but composed of a material having more desirable electronic properties. A polymer can be applied over the surface of the ZnO nanorod films before etching the ZnO with a weak acid, thereby leaving a polymer nanopore membrane. Cathodic electrodeposition of Cu2O into the membrane nanopores gives Cu2O nanorods. Electron-accepting dyes are designed with tethers that allow for direct attachment to metal oxide semiconductors. After soaking, the semiconductor is coated with a monolayer of a dye and then the coated semiconductor films were made into various dye-sensitized solar cells (DSCs). These cells were studied to determine the electron transport properties at the semiconductor/sensitizer/electrolyte interface.

Solar cells are designed to transform the optical energy into electrical energy. Using solar energy is the best way for humans to solve the energy shortage problem. Dye sensitized solar cell(DSSC) has a low cost and helps people to obtain the solar energy expediently. The DSSC is based on nano structured TiO2 ; and dye molecules help the particles of TiO2 to absorb more photons. Hence DSSC has higher efficiency than SC(solar cell without dye). This thesis elaborates and analyzes the dye which is sensitized to TiO2. The absorption spectrum of the dye was achieved. Two kinds of dye sample were made on the basis of their places in structure of TiO2. One dye sample is solution, nanopowder of the dye in aceton. The other dye sample is film, thin film on a quartz plate. The absorption spectrums of the samples have been measured in laboratory. The measurement suggests that the dye works improves the absorption of solar energy in DSSC. This thesis mainly contains the following sections: Chapter I reviews the solar energy technology development, the research purposes, and the principles of DSSC. Chapter II introduces the theory of optical spectroscopy. Chapter III and Chapter IV describe the apparatus employed in this experimental system, the experimental method, and the testing results. Chapter V gives the conclusions drawn from the experiments.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第21124号 / 工博第4488号 / 新制||工||1697(附属図書館) / 京都大学大学院工学研究科高分子化学専攻 / (主査)教授 辻井 敬亘, 教授 山子 茂, 教授 竹中 幹人 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

This master thesis is the last part of the master program Production Engineering and Management at the Royal Institute of Technology, KTH, in Stockholm. The thesis is conducted at Exeger Operations AB, in short Exeger. The company is in an expansion phase and wants to prepare for future production expansion. Thus, a simulation capability to test future production scenarios was desirable. The problem definition was defined by the company together with the authors and led to a literature study within simulation, TPS and Lean manufacturing. Following the literature study, a current state map was produced to achieve sufficient understanding of the production flow at the company. A simulation model was then built. The model was used to test three different ”what-if” scenarios. Buy or Optimize, Future ratio 3:1:1 and Buy or SMED. The authors’ findings in the Buy or Optimize scenario suggest that optimizing the process time in the printers is far better, from multiple perspectives, than investing in new machinery. A 3:1:1 ratio of printers, sinter 1 and assembly station was developed using the simulation model to achieve leveled production flow of these specific processes. Lastly, conducting a SMED on the sinter 1 machine, the setup-,and wait-times achieved a theoretical reduction up to 75 % by altering the SOP and allocating additional preparatory space, in accordance with Lean philosophy. This change would offer the same improvement to a full-scale production as investing in a new sinter 1 according to the simulation model. Future work may consist of Layout Planning and adopting the simulation model to new prerequisites.

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Dye-sensitized solar cells (DSC) have attracted considerable scientific and industrial interest during the past decade as an economically feasible alternative to conventional photovoltaic devices. DSCs have the potential to be as efficient as silicon solar cells, but at a fraction of the cost of silicon solar cells. The unique advantage of DSC compared to conventional solar cells is that the light absorption, electron transport and hole transport are handled by different components which reduces the chance of recombination. In the present work, to facilitate DSC with good energy conversion efficiency, its performance have been evaluated as a function of titania layer morphology, redox couple concentration and the catalytic layer on the counter electrode. The results that are obtained in the present investigations have been organized as follows Chapter 1 gives a brief exposure to DSC technology. Special emphasize has been on the structure and individual components of the DSC. Chapter 2 describes various experimental techniques that are employed to fabricate and characterize DSCs under study. Chapter 3 presents a systematic study of the characteristics of DSC made of three different types of electrodes namely: TiO2 nanotubes (TNT) which have excellent electron transport properties, TiO2 microspheres (TMS) which possess high surface area and light scattering ability and TiO2 nano particles (TNP) possessing high surface area. The electronic, morphological, optical and surface properties of individual electrodes are studied. The highest efficiency of 8.03% is obtained for DSCs prepared with TMS electrodes. A higher value of effective diffusion coefficient (Deff) and diffusion length (Ln) of electrons as obtained by electrochemical impedance spectroscopy (EIS) analysis confirms a high charge collection efficiency in microsphere based cell. Chapter 4 gives a detailed study of DSCs fabricated with a tri-layer photo anode with TNTs as light scattering layer. The tri-layer structure has given an enhanced efficiency of 7.15% which is 16% higher than TNP based cell and 40% higher than TNT based cells. Chapter 5 deals with the investigations on the effect of concentration of redox couple on the photovoltaic properties of DSC for different ratios of [I2] to [LiI] (1:2, 1:5 and 1:10) with five viii concentrations of I2 namely 0.01 M, 0.03 M, 0.05 M, 0.08 M and 0.1M in acetonitrile. It is found that the open circuit potential (Voc) decreases with increase in the ratio of redox couple whereas short circuit current density (Jsc) and fill factor (FF) increase. The reason for the decline in Voc is the higher recombination between electrons in the conduction band of TiO2 and the I3- ions present in the electrolyte, induced by the absorptive Li+ ions. In addition using EIS it is found that the τ improves with the increase in [LiI] at a particular [I2], whereas at a fixed [I2]/ [LiI] ratio the increase in [I2] is found to reduce the τ and Deff due to the enhanced recombination. Chapter 6 describes the application of carbon based counter electrode (CE) materials for DSCs. Two counter electrode materials have been investigated namely (1) Multiwalled carbon nanotubes (MWCNT) synthesized by pyrolysis method and (2) Platinum decorated multiwalled carbon nanotubes (Pt/MWCNT) prepared by chemical reduction of platinum precursors. Using Pt/MWCNT composite electrode the DSC achieved an energy conversion efficiency of 6.5 %. From the analysis on symmetric cells, it is found that electro catalytic activity of Pt/MWCNT CE is similar to that of platinum CE, though the platinum loading is very less for the former. This is attributed to the effective utilization of catalyst owing to high surface area arising from the increased surface roughness. Chapter 7 discusses the application of titanium foil in place of glass substrate for the photo anode. The titanium foil offers fabrication of flexible DSC. The performance of DSC with TMS layers and aligned titania nanotube arrays (TNA) prepared by anodization method is studied. Compared to TMS based cell, TNA has given a better efficiency at a lower thickness. Chapter 8 presents the scheme used to seal DSCs and its stability analysis. We have employed the usual hot melt sealing for edge whereas hole sealing is carried out with tooth pick and a UV curable adhesive. The degradation in efficiency is found to be 20% for low efficiency cells whereas, for high efficiency cells it is found to be 45% after 45 days. The leakage of highly volatile acetonitrile through the edge and hole is found to be responsible for the reduction in the performance of the device. Hence a high temperature sealing method is proposed to fabricate stable cells. Chapter 9 gives summary and conclusions of the present work