The Research On Photo-anodes Of Dye-sensitized Solar Cells

There has been a growing industrial interest in dye-sensitized solar cells as an alternative to the traditional silicon-based solar cells because of their low-cost, simple fabrication process and high-energy conversion efficiency. As the working electrodes of dye-sensitized solar cells, the surface and internal electrical characteristics of the mesoporous nanocrystalline TiO2 photo-anodes determine the energy conversion efficiency of the solar cells. During the past decades, the investigation of TiO2 photo-anodes was mainly focused on the preparation method and film process, the researches on the mechanism of charge transport in the TiO2 electrode and the interface characteristics of the TiO2 electrode and electrolyte. However, there is still not a simple preparation method, which could be used to control the particle size and the feature of the nanoparticles effectively. Thus, it is necessary to improve the production process of the TiO2 thin film, including the choice of process parameters such as the particle diameter, specific surface area and thickness of the thin film, and the improvement of the TiO2 electrode material and structure. Hence, it is very important to investigate the TiO2 electrode.Herein, the TiO2 photo-anodes are investigated thoroughly from the aspects of theorety and experiment. Theoretically, the doping effect on the electronic density distribution and energy band structure are analyzed and performed by the first principles calculation. Furthermore, the effect of Nitrogen and Tantalum ions doping on DSSC is also discussed. Experimentally, TiO2 nanoparticles with different particle size, nitrogen-doped TiO2 microspheres and tantalum doping TiO2 microspheres are prepared by hydrothermal method. And the measurement and analysis of these samples which may affect the properties of the solar cells are also done. The main works are discussed as following.(1) The nanocrystal TiO2 particles are synthesized by hydrothermal method, and the growth situations of TiO2 under different hydrothermal conditions are investigated. Then, the electrodes, which are used to assemble the cell, are designed with TiO2 particles of different grain size. It is found that the grain size of TiO2 will increase with reducing nitric acid, elongating hydrothermal growth time or increasing hydrothermal growth temperature. Meanwhile, the liquid solar cells are assembled with TiO2 electrode composing of the nanoparticle size in the range of 10-25 nm. The highest efficiency (7.20%) is obtained with 20nm TiO2.(2) The influence of nitrogen doping on TiO2 electronic band structure are studied by first principles calculations. Meanwhile a comparison is proposed with the case of TiO2 oxygen vacancies on TiO2 electronic band structure based on density functional theory. The N doping effect on the cells is also discussed.(3) A series of N-doped TiO2 mesoscopic spheres are synthesized by hydrothermal method. The experiments of the electrode visage, theâ… -â…¤and electrochemistry characteristics with different N content are carried out. The experiments result suggests that N doping improved the Joc, Voc and photovoltaic performance, and it agrees well with the theoretical calculation. Meanwhile, the photoelectron chemistry properties for both nitrogen-doped and undoped TiO2 spheres are performed with MS, EIS and IMPS. These results indicate that with the flat-band potential of N-doped version shifts negatively, and the resistance between the electrode and electrolyte is increased, the interfacial recombination is decreased. Therefore, higher photovoltaic Voc could be obtained. Moreover, the electronic transport velocity is also promoted, and the photocurrent density Jsc could be decreased. As a result, a power conversion efficiency up to 6.01% under AM 1.5 sunlight at 100 mW/cm2 has been obtained with N719 dye in combination with a quasi-solid state electrolyte.(4) The electronic band structure of TiO2 with tantalum-doped is investigated by the first principle, wherein Ti located on different coordination is replaced by Ta. The Ta doping effect on the cells is also discussed.(5) A series of Ta-doped TiO2 mesoscopic spheres are synthesized by hydrothermal method. Moreover, the affection of hydrothermal temperature and the Ta content on the characterization of photo-anode, theâ… -â…¤and the electrochemistry characteristics are also discussed. The results indicated that the hydrothermal temperature and Ta content could affect obviously on the performance of the cells, which is agreed well with the theoretical results. As a result, a power conversion efficiency of quasi-solid state dye-sensitized solar cells has been reached to 6.97%.