Application Of FTO @ TiO 2 Photocathode Materials In Dye - Sensitized Solar Cells

Drying up of Energy has became a common problem of the whole world to be solved, meanwhile combusting a large number of fossil fuel has caused serious environmental pollution which is becoming a threat to human survival and sustainable development. Utilizing clean and plentiful solar energy is the key to solve the problem of energy shortage and environmental pollution. Dye-sensitized solar cells (DSSC) are believed to be a formidable competitor to realize large-scale transformation of solar energy to electricity due to its advantages of non-toxic, low cost, and easy manufacture. And photoanodes, whose composition and structure directly impact the photoelectric conversion efficiency and long-term stability of cells, are the most important part of DSSC. But in current studies, DSSC has a long way to go to achieve the photoelectric conversion efficiency in theory. There exist many problems to be solved, such as electronic transport is very slow in TiO2 nano membrane, and injected electron is easy to recombine with I3 in electrolyte or dye cations and so on, these further restrict the improvement of DSSC photoelectric performance.This paper is aimed at further accelerating the electron transfer rate of photoanode film, improving the electronic collection efficiency and reducing the electron recombination. Employing FTO@TiO2 film instead of common TiO2 film, because of its electronic drift mechanism, can speed up the electronic transportation and collection efficiency. At the same time in order to inhibit the electron recombination, Al2O3 barrier layer is coated on the surface of FTO@TiO2 film. Because the thickness of Al2O3 layer will exert influence on the photoelectric performance of DSSC, so to determine the optimum thickness of Al2O3 layer through research is necessary to realize the maximum photoelectric efficiency of the DSSC. The main research contents and research results are as follows:(1) Synthesizing FTO nanoparticles through sol-gel method. The percentage of dopant F atoms was changed by adjusting the amount of HF added in synthetic process. The resulting products 0.15 FTO,0.3 FTO and 0.6 FTO were studied by XRD, EDS, TEM and UV-vis absorption spectroscopy to understand the properties of crystal structure, composition, morphology, particle size, morphology, and the band gap etc.(2) A certain proportion of FTO powder, PVDF binder and N-methyl pyrrolidone was ground in a ball mill to get FTO paste, three kinds of FTO nanoparticulate film, 0.15 FTO,0.3 FTO and 0.6 FTO, were prepared by doctor blading a thin layer of FTO paste with an area of 0.36 cm2 and sintered at 450℃ for 30 min. After TiCl4 treatment, 0.15 F-T,0.3 F-T and 0.6 F-T films were obtained and used as photoanodes of DSSC. Comparing the photoelectric efficiencies of three types of DSSC,0.3 F-T DSSC is found to achieve the highest efficiency 6.13%, which has a close relationship with the doping amount of F. The higher the doping amount of F, the larger the band gap of FTO and the higher the Fermi level of FTO are, as a result, corresponding with a higher Voc. Besides the conductivity of the FTO becomes higher, higher electronic extraction efficiency is achieved but not higher electronic injection efficiency because of the reduced Fermi level. So 0.3 F-T DSSC instead of 0.6 F-T DSSC has the highest photoelectric efficiency. At the same time, effective electronic extraction from TiO2 layer to FTO layer also makes contributions to the high photoelectric efficiency.(3) At the base of 0.3 F-T (referred as F-T) DSSC holding the highest photoelectric efficiency, in order to further restrain electronic recombination and reduce back transfer of electrons, F-T photoanode film was coated with an Al2O3 barrier layer by using sol-gel method. Al2O3 layer can not only inhibit electronic recombination, but also reduce the electron injection efficiency. There exists an optimum film thickness. By comparing the photoelectric efficiencies of F-T-A, F-T-2A and F-T-3A DSSC, it is found F-T-2A DSSC with two times of Al2O3 coating has the highest efficiency 6.89%. The dark J-V curve and EIS test show that coating two Al2O3 layers which is about 2 nm thick makes electronic recombination and injection reach a perfect balance, which is proved by a moderate recombiantion resistance and a smallest electronic transfer resistance.