Dye-sensitized solar cells (DSCs) convert sunlight to electricity at a low cost. In the DSC, a dye anchored to a mesoporous TiO2 semiconductor is responsible for capturing the sunlight. The resulting excited dye injects an electron into the conduction band of the TiO2 and is in turn regenerated by a redox mediator, normally iodide/triiodide, in a surrounding electrolyte. The success of the iodide/triiodide redox couple is mainly attributed to its slow interception of electrons at the TiO2 surface, which suppresses recombination losses in the DSC. One of the main limitations with the iodide/triiodide redox couple is, however, the large driving force needed for regeneration, which minimizes the open circuit voltage and thus the energy conversion efficiency. In this thesis, alternative redox couples to the iodide/triiodide redox couple have been investigated. These redox couples include the one-electron transition metal complexes, ferrocene and cobalt polypyridine complexes. The use of one-electron redox couples in the DSC has previously been shown to lead to poor photovoltaic performances, because of increased recombination. Cobalt redox couples were here found to give surprisingly high efficiencies in combination with the triphenylamine-based organic dye, D35. The success of the D35 dye, in combination with cobalt redox couples, was mainly attributed to the introduction of steric alkoxy chains on the dye, which supress recombination losses. By introducing steric substituents on the dye, rather than on the redox couple, mass transport limitations could in addition be avoided, which previously has been suggested to limit the performance of cobalt complexes in the DSC. The result of this study formed the basis for the world record efficiency of DSCs of 12.3 % using cobalt redox couples. Interfacial electron-transfer processes in cobalt-based DSCs were investigated to gain information of advantages and limitations using cobalt redox couples in the DSC. The redox potentials of cobalt redox couples are easily tuned by changing the coordination sphere of the complexes, and regeneration and recombination kinetics were systematically investigated by increasing the redox potential of the cobalt complexes. Our hope is that this thesis can be a guideline for future design of new redox systems in DSCs.

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In this study, we used two types of materials as working electrode of DSSC, commercial TiO2 (P25) nanoparticle and ZnO nanotip. First part, we sintered TiO2 electrode in nitrogen and treat TiO2 electrode by UV light irradiation, in order to increase dye adsorption onto TiO2. Second part, we used three different buffer layers to grow ASD-ZnO nanotip as working electrode, sputtered-ZnO, sputtered-AZO and spin-coating TiO2. The hetrojuction is formed at the interface of ZnO nanotip/TiO2 buffer layers due to the different materials between ZnO and TiO2, which is beneficial for electron-hole separation. The morphology was measured by field emission scanning electron microscope (FE-SEM, Philip XL-40FEG). The sheet resistivity was measured by four-point probe. The crystallinity was examined by X-Ray diffraction (XRD, Simens D5000). Structural and spectral properties are characterized by ultraviolet-visible spectroscopy (UV-Vis) spectroscopy. The fourier transform infrared spectroscopy (FT-IR spectroscopy, BRUKER 66v/s) deals with the infrared region of absorption spectroscopy. And the Angilent B1500A is used for current-voltage (I-V) characterization of solar cells. In our results, we enhance the performance of TiO2 electrode DSSC, the open circuit voltage can reach to 0.56 V, the short circuit current density can reach to 16.65 mA/cm2, the conversion efficiency can reach to 4.6 % and the fill factor can reach to 49.2 %. On ZnO electrode, the open circuit voltage can reach to 0.57 V, the short circuit current density can reach to 4.43 mA/cm2, the conversion efficiency can reach to 1.21 % and the fill factor can reach to 47.9 %.

Nitrogen oxide in water was a critical factor of eutrophication. The poor tap-water quality in Taiwan was the result of ammonia nitrogen pollution. This research used manganese dioxide as the catalyst to degrade ammonia nitrogen content in water. Controlled factors in our experiment include basic test, optimal reaction condition test, and kinetics. Real water sample was drawn from the Love River for catalysis effect test. Results were then compared with the popularly used titanium dioxide. Significant findings in this research include: 1) when the manganese dioxide content in water was 2%, the ammonia nitrogen removal rates were 31.80% under UV irradiation, and 22.21 % without light interference; 2) under UV irradiation, manganese dioxide would not affect the catalysis effect due to pH changes; 3) silicate in the water had catalysis effect, while sulfate, phosphate, and nitrate had inhibition effect; 4) manganese dioxide had catalysis effect in seawater, yet the removal rate would decrease as the salt content increases; 5) the rise of water temperature would enhance the ammonia nitrogen removal rate; 6) manganese dioxide had catalysis effect on the treatment of the Love River water, and the ammonia nitrogen removal rate reached 89.50 %; 7) in the biological test, manganese dioxide could effectively degrade the ammonia nitrogen content in water, and improve the survival rate of larval shrimp; 8) comparing to titanium dioxide, manganese dioxide had advantages of low cost, with catalysis effect in both seawater and fresh water under no light condition. As a result, manganese dioxide has significant future application potentials. In the future, this research will conduct in-depth study on kinetics of degradability of manganese dioxide catalysis on ammonia nitrogen, and to design suitable catalytic reactor for water treatment. Moreover, it is of value to broadly research manganese dioxide related catalytic products, such as catalytic spray, catalytic paint, fluorescent tube, air filter, and catalytic fan...etc.

In this study, we deposit titanium dioxide (TiO2) on the indium tin oxide (ITO/glass) substrate by a liquid phase deposition (LPD) method as a buffer layer and coat TiO¬2 particles on LPD-TiO2 films by spin-coating method as anode of dye-sensitize solar cell (DSSC). In order to adjust the optical absorption edge of titanium dioxide to the visible light, we co-dope fluorine and nitrogen into TiO2 by LPD method and Ammonium Fluoride (NH4F). In our experiment, the morphology and thickness was characterized by scanning electron microscopy (SEM), structure was characterized by X-ray diffraction (XRD), chemical properties was characterized by electron spectroscope chemical analysis (ESCA), structural and spectral properties were characterized by ultraviolet-visible spectroscopy (UV-Vis) spectroscopy and current-voltage (I-V) characterization of solar cells was measured by B1500A. In our results, we enhance the performance of TiO2 as a DSSC`s anode, the open circuit voltage can reach to 0.71 V, the short circuit current can reach to 5.14 mA, the conversion efficiency can reach to 1.91 % and the fill factor can reach to 52.5 %.

Thesis (Ph. D.)--Institute of Paper Chemistry, 1942. / Includes bibliographical references (p. 83-84).

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In this thesis, we explore titanium dioxide (TiO2) for ultrafast, on-chip nonlinear optics by studying it in bulk, thin films, and in integrated nonlinear optical devices. TiO2's large nonlinear index of refraction (30 times that of silica) and low two-photon absorption can enable all-optical switching, logic, and wavelength conversion across wavelengths spanning the telecommunications octave (800–1600 nm). In addition, its high linear index of refraction can enhance optical confinement down to nano-scale dimensions and facilitate the tight waveguide bends necessary for dense on-chip integration. Throughout this thesis, we develop TiO2 as a novel on-chip nonlinear optics platform. / Engineering and Applied Sciences

Στην παρούσα πτυχιακή παρασκευάστηκαν νανοσύνθετα υλικά TiO290-HALL10 και TiO280-HALL20 ώστε να εφαρµοστούν στην φωτοκαταλυτική αποδόµηση αερίων ρύπων. Τα νανοσύνθετα παρασκευάστηκαν µε τη µέθοδο διασποράς-επικάθισης του TiO2 και στους επιµήκεις κρυστάλλους του Αλλουσίτη.Η κρυσταλλική µορφή του TiO2 που συντέθηκε ήταν ο ανατάσης. Εφαρµόστηκαν οι παρακάτω τεχνικές:περιθλασιµετρία ακτίνων X(XRD), υπέρυθρη φασµατοσκοπία µετασχηµατισµού κατά Fourier(ATR-FTIR), ηλεκτρονική µικροσκοπία σάρωσης(SEM),προσδιορισµός µεγέθους και κατανοµής πόρων καθώς και ειδικής επιφάνειας. Tα νανοσύνθετα υλικά λόγω των ιδιοτήτων τους φαίνεται να είναι αποτελεσµατικά στην εφαρµογή τους στους αέριους ρύπους και έτσι µπορούν να χρησιµοποιηθούν και στις οργανικές πτητικές ενώσεις. / In this study were prepared nanocomposites TiO290-HALL10 and TiO280-HALL20 order to be applied in several environmental applications. The samples were prepared by dispersing TiO2 nanoparticles on the microfabers of alloysite. The crystal form of TiO2 that was synthesized was anatase. The nanocomposites were characterized using the following techniques:X-ray diffraction(XRD), scanning electron microscopy(SEM), attenuated total reflection using Fourier transform infrared spectroscopy (ATR-FTIR) and N2 surface analysis by BET. The nanocomposites due to their characteristics showing to be effective in decomposing air pollutants and can be used in volatile organic compounds.

My research on metal oxide electron-harvesting interlayers for organic solar cells was focused as three interrelated projects in this dissertation: i) development of a chemical vapor deposition (CVD) system for titanium dioxide (TiO₂) film; ii) an electrochemical methodology to evaluate ZnO thin film charge (hole) blocking ability; iii) the effects of plasma modifications on sol-gel ZnO and sol-gel ZnO/organic (active layer) interfaces. In i), we showed that nanoscale (12-36 nm) CVD TiO₂ film deposited at 210 °C from our system obtains properties of conformal growth with ITO substrate, superior hole blocking ability, stoichiometric metal to oxide ratio, and close energetic alignment with electron acceptors, e.g., fullerenes. The introduction of CVD TiO₂ film as an electron transport layer (ETL) into organic solar cell significantly improves its J-V characteristics compared to bare ITO electrode. The optimum TiO₂ thickness in the OPV device applications was found to be 24 nm with a high fill factor (0.58) and power conversion efficiency (3.7%) obtained. In ii), simple electrochemical methods, i.e., cyclic voltammetry, impedance spectroscopy have been used to evaluate sol-gel derived ZnO (sg-ZnO) and sputtered ZnO (sp-ZnO) porosity and pinhole density. We showed that sg-ZnO with high surface area porous structure allows the probe molecules and poly-thiophene (P3HT) thin layer to direct contact ITO substrate, whereas sp-ZnO with dense structural property efficiently eliminates the probe molecule diffusion and the penetration of P3HT layer to ITO substrate. This electrochemical property difference also directly reflects on the device shunt resistance (Rp), where we observed larger leakage current for the devices using sg-ZnO than that of devices using sp-ZnO. We envision these simple electrochemical characterizations can be applied into other similar metal oxide interlayers as well as on flexible TCO substrates, in which pinholes and physical imperfections, e.g., cracking may occur after multiple bending processes. In iii), we demonstrated low power (10.5 watts) radio frequency (RF) O₂ and Ar plasma treatments have significant impacts on sg-ZnO near-surface chemical compositions, which in turn influence the onset potential of sg-ZnO electron injection from the underlying ITO substrate and its energetic alignment with electron acceptors, e.g., C₆₀. Using UPS, we found the presence of localized mid-gap states near the Fermi-level (Ef) of sg-ZnO, which induces the most favorable band bending and the largest vacuum level shift due to significant electron transfer from sg-ZnO to C₆₀. As a result, the resultant solar cells show the best device performance. Upon the plasma treatments, the passivation effects eliminate the mid-gap state. Therefore, we observed less degree of band bending at ZnO/C₆₀ interface and poorer device performance for the plasma treated sg-ZnO. The study demonstrates the importance of oxide/organics interface in operations of organic solar cells and provides a modification method to tune surface properties of oxide materials which can apparently be applied in other organic electronic devices, e.g., field effect transistors (FETs), organic light emitting diodes (OLEDs), etc.