| TiO2 is an important metal oxide in the fields of photocatalyst and photovotaics, is an indispensible semiconductor controlable until nanoscale, suitable to be prepared as photoanode on various substrates. Application of organic dyes, quantum dots, conducting polymers to sensitize TiO2 will overcome the limitation of its absorption only to UV, as well break the bottleneck of low conversion efficiency. But TiO2 itself is the most important deciding factor. The best way is to change its crystal structure and electronic structure during growth to broaden its absorbed spectral range.The first chapter is the introduction, describes the research background, origin, meaning and importance of our work. The first part introduced the development and mechanism of TiO2, the structure, properties and applications of TiO2 film. The research status and applications in photocatalysis of TiO2 film were also summarized. The structure of nano-TiO2, mechanism of photocatalysis and photovoltaics, the preparation methods of TiO2 powders and nano-single-crystals, the improvement of TiO2 photocatalytic activity and its applications were introduced in last part.The experimental methods, characterization methods and test equipments in the various parts of work are described in the second chapter. It includes:the mechanism, process and methods of TiO2 nanoachitectures preparation on the substrate of Ti, the doping of TiO2 film compounded with semiconductors, and the hydrogenation of P25 TiO2 nanoparticles. The characterization and measurement of the morphologies, microstructures, TiO2 films and other samples by SEM, EDS, TEM, HRTEM, XRD, XPS, Raman, UV-VIS absorbance spectrum, photo-generated current and electrochemical principles and techniques were also introduced.In the third chapter, the rich micro structural variation of the TiO2 nano crystalline film on the substrate of Ti, was found by using SEM, TEM, HRTEM and XRD:there are single crystal (confirmed by HRTEM) nanopillars, as well closely connected networks of around 10 nm. Raman Spectrascopy, XRD, XPS, EPR, FTIR, UV-Vis were applied to characterize the the morpologies, the chemical components, crystalline structures, chemical bonds, photonic absorption. The major achievments are:(1) compared with general TiO2 nanoparticles theVBM obtained of TiO2 nanoarchitectures shifts towards CBM 2 eV at most (meaning 2 eV bandgap reduced at least), this was possiblely led by N-and C-self-doping into TiO2 crystalline structures, forming Ti-N and Ti-C bonds etc, or even by self-hydrogenation; EPR confirms there are three g values; (2) Raman Spectrascopy and cyclic voltammetry confirmed there are O vacancy defects below the CBM, so that the bandgap was reduced further; (3) These combined reasons produced considerable photocurrents, with Jsc scaled to 0.1 mA cm-2 in dark without any dyes in polysulfite solution.In the fourth chapter, the effects of CdSe sensitzation on Ti/TiO2 performances were studied, (1) CdSe sensitzation layer from SeO32- source was introduced onto TiO2 electrodes, rich phenomena of photoelectric conversion were found. (2) TiO2 nanoclusters-CdSe linked by cystein could produce currents under UV as well as visible light, about according to the power. (3) Hydrothermal-Solvent thermal two-step synthesis of TIO2 nanostructure was conducted, TiCl4-CdSe treatment was processed, in which CdSe renders TiO2 a dark photovoltaic effect, and around 1.2mA·cm-2 under UV. (4) 180℃-TiO2 (5ml-,10ml-) were investigated about the TiCl4/CdSe treatment effect on dark photovoltaics, which decays the performance. (5) doping NaCl, KCl in the hydrothermal process of TiO2 could change TiO2 as follows:NaCl-TiO2 produces dark photovoltaic currents beyond CdSe modification; KCl-TiO2 photovoltaic currents far below the former, and suffers to CdSe modification.In the fifth chapter, the major challenge of introduction of conducting polymer into nanoachitectural TiO2 and formation of bi-continuous phase of distinct electron-and hole-transport paths was met:PPy/TiO2 heterojunction was prepared and characterized, as an organic-inorganic p-n junctional solar cell, with conducting polymer to act as p-semiconductor, simutaneously as solid electrolyte. (1) using current pulse a PPy(TSA)/TiO2 nanoachitectural anode was prepared, and a layer of Au was coated by thermal evaporation to achieve Jsc 12.5 mA cm-2 at 1 sun with conversion efficiency 1%, so that it provides a novel approach to study the TiO2 solid solar cell with PPy. (2) using photoanodic polymerization method a PPy (C1O4-)/ TiO2 nanoachitectural anode was prepared, and the formation of heterojunction was labelled by a photocurrent of 0.1 mA cm-2, and an improved dark photocurrent about 20 times of only TiO2.Chapter six is a full summary. Finally, a brief introduction of published papers, participated projects honors, Curriculum Vitae and acknowledgements in the graduate were given. |
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