Preparation And Performance Of Nanometer TiO₂ For Dye-sensitized Solar Cells

Titanium dioxide is one of the most widely studied semiconduetor materials with good chemical stability,safety and non-toxic,long operating life,low production cost,and has wide application promising in the field of solar cell.However,the shape and structural control of titanium dioxide is a research hotspot in the field of dye-sensitized solar cells（DSSC）. Solvothermal/sol-gel technique is a good way to get anatase TiO₂ nanorod and modified TiO₂.In this dissertation,we have systematically studied controllable preparation of nanorod TiO₂ via Solvothermal/sol-gel synthesis method using cetyl trimethyl ammonium bromide（CTAB） as molecular template,organic amines as structural guide reagent.Furthermore,the effect of Solvothermal reaction time,temperature and the kind of organic amine on size and morphology of TiO₂ were systematically investigated.The results indicate that the development（size and morphology） of TiO₂ nanocrystals was influenced by the Solvothermal reaction time,temperature and the kind of organic amine.The morphology of TiO₂ was grown from irregular spherical,to short rod-like particle,at last to regular long rod-like particle with increase of Solvothermal reaction time from 6 h to 12 h.However,the morphology don’t obviously change when the reaction time increase from 12 h to 24 h.Simultaneously,it was also found that the morphology of TiO₂ is regular nanorod TiO₂ using primary amine as structure guide reagent;The morphology shows irregular nanorod TiO₂ using secondary amine as structure guide reagent;the ellipsoid-like TiO₂ is obtained when using tertiary amine as structure guide reagent.The structure and property of nanorod TiO₂ modified by doping transition metal ions were investigated vis XRD,XPS,UV-vis methods.The XRD results diaply that a new phase is found at high doping concentration such as doping concentration for Cd²⁺ at 5 wt%,Zn²at 11%,Cr³⁺ at 5%, Fe³⁺ at 6%.At lower than above doping concentration the single phase of doped TiO₂ were obained,which the transition metal ions exist by taking place of the Ti⁴⁺ woing to their similar ion radii and electronegativity with Ti⁴⁺.The UV-vis spectra show that the absorbing band edge of all samples appears red shift.It is just that a new chemistry condition is created by doping transition metal ions to result in a new energy level,which reduces the band gap and results in red shift of absorbing band edge.In order to further exploit the doping mechanism,First-principles based on the density functional theory（DFT） was employed to investigate influencing mechanism of Cd,Zn,Cr,Fe -dopd on the energy level structure of anatase TiO₂.The result indicatied that there exists a new energy level in doped TiO₂,an interlaced energy level,which changes the position of conduction band.