Preparation And Sensitization Of Nanocrystalline TiO₂Thin Films

Dye-sensitized solar cells have great development potential because of its highphotoelectric conversion efficiency in theory, easy preparation and low cost. We preparedseveral different kinds of nanocrystalline TiO₂films and several testing technologieswere used to research their characteristics. Besides, we tested the spectral properties ofrhodamine B, asymmetric squaraine indocyanine dye,4-Aminoazobenzene andfluorescein.Nanocrystalline TiO₂thin film was prepared on ITO conductive glass by sol-gelmethod at room temperature. During the reaction, tetrabutyl titanate （TBOT） was used asprecursor, ethanol was used as solvent, diethanol amine as chelating agent andpolyethylene glycols （PEG） as surfactant. On that basis, acetic acid and ammonia werechosen as catalysts to prepare two new kinds of sol. XRD tests confirmed that the crystalform of normal nanocrystalline TiO₂thin films was anatase in a great measure, and TiO₂films added with acetic acid or ammonia as catalysts were both the mixed phase ofanatase and rutile, this indicated that rutile was more likely to be created when addingacid or alkali in the sol; step profiler tests showed us that the average thickness of normalTiO₂film was the most flimsy, and the films added with ammonia were the thickest.Besides, the field emission scanning electron microscope tests and atom forcemicroscope tests proved that，the particle size of TiO₂grain prepared under acetic acidcondition was the smallest and the roughness of the TiO₂film was the lowest, and theparticle size and roughness of the TiO₂films prepared under ammonia catalytic conditionwere the biggest. We prepared several different laminate TiO₂films and tested bothspectra and photoelectric properties after they were sensitized. When the grains in outerlayer were larger than those in inner layers, the photoelectric properties of the DSSCwere better.The maximum UV-Vis absorption wavelengths of rhodamine B, asymmetricsquaraine indocyanine dye,4-Aminoazobenzene and fluorescein were544nm,630nm,384.5nm and485nm in methanol, respectively, and absorption intensity of them grewhigher with increase of their concentrations. We added α and β-cyclodextrin to these dyes to explore whether they had interact with each other, and the results indicated there wasno significant change in the spectrum of rhodamine B or fluorescein, but the fluorescenceemission intensity of the asymmetric squaraine indocyanine dye enhanced withcyclodextrin, but the fluorescence emission intensity of the4-Aminoazobenzenedecreased.The nano-TiO₂thin films were sensitized with the dyes by impregnation method andnew sensitizing method, respectively. The results confirmed that new sensitizing methodhad good effect for sensitizing the films and advanced the photoelectric properties of theDSSC. The Voc and Isc of the DSSC could achieve0.517V and0.320mA, respectively.