Study On The Fabrication And Photoelectric Properties Of Sn⁴⁺、Sb³⁺、Nb⁵⁺ Doped Titanium Dioxide Nanomaterials

Titanium dioxide has good chemical stability, pollution-free, corrosion-resistant, cheap price and otheradvantages. There are broad application prospects in solar cells, the photocatalytic degradation of organicmatter, hydrogen energy generation. However, TiO2can only absorb ultraviolet light (≤387nm), whichhamper the effective use of sunlight, and its application were also limited. In order to widen the band edgeabsorption of titanium dioxide, these strategies were used such as metal ion doping, non-metal and metalion codoped, narrow band-gap semiconductor compound, surface treatment and other methods to improveTiO2ability to respond to visible light. However, it becomes a key bottleneck restricting TiO2widerapplication due to the weaker photoelectric properties of TiO2in the visible light region. Therefore, in viewof this problem we have expanded the preparation and photoelectric properties of metal ion doped TiO2nanomaterials. The specific research content is as follows:In the second chapter, we prepared titanium dioxide and different tin doping amount of titaniumdioxide nanorods films by the hydrothermal synthesis method using tetrabutyl titanate as precursor underthe strongly acidic conditions. Then we use the different characterization techniques such as XRD, Raman,SEM to carry out a detailed study and analysis. The results have shown that tin doping has not changecrystal phase and morphology of titanium dioxide. Sn-doped titanium dioxide can widen its absorption tothe visible light region using UV-vis diffuse reflectance spectroscopy. XPS results showed that the peaksat about486.4eV and495.2eV correspond to the binding energies Sn3d5/2and Sn3d3/2, respectively. Thisindicates that tin was doped into the TiO2lattice in the form of Sn4+. Then we compound CdS nanoparticleson the samples using CBD method. And the photoelectric properties of samples were tested usingthe polysulfide as electrolyte and Cu2S as the counter electrode. The results indicate that higherphotoelectric conversion efficiency of devices was obtained at higher Sn doping concentration. This is dueto tin doping increasing the density and transmission efficiency of carrier.In the third chapter, we prepared TiO2nanorods array films with the different antimony dopedconcentration using the above synthesis method. After Sb-doped, the structural and morphologycharacterization still displayed rutile structure and the morphology of nanorods, respectively. Light absorption performance indicates the absorption band edge of Sb-doped samples slightly red shift. Becauseof Sb3d peak at529.6eV near to O1s binding energy at530eV, it is not easily distinguished. AndSb3d3/2peak was also not detected, whose binding energy is at537.6eV. So it indicated that much lowerSb doped concentration was in the samples. After CdS quantum dots sensitized, the photoelectricperformance tests showed that Sb doped is more efficient than Sn doped. This is due to the increase of thecarrier density and the better transmission efficiency after Sb-doped.Then, Sn and Sb-doped samples were surface treated. One approach is that the samples are annealedunder the H2/Ar atmosphere (the volume ratio of H2is5%) for30min. The second method is that thesamples are annealed under the NH3atmosphere for30min. Then, we used SEM, XRD, Raman, UV-visspectroscopy techniques to investigate samples for characterization. The results showed that the samples’morphology and crystalline structure annealed under the different atmosphere has not change. Only thedisordered layer was formed on the surface of the samples. At the same time, the visible light absorption ofthe samples after hydrogenation and nitrided surface treatment extends to700nm and550nm, respectively.But the effect on the photoelectric conversion efficiency is different. Under the H2atmosphere, probablydue to increased surface oxygen vacancies, electron-hole can be better separated. At last, it resulted inenhancing short-circuit current density and increasing the conversion efficiency. Whereas, the samplesannealed under the NH3atmosphere absorbed more photons, and effectively promoted the separation ofphotogenerated electrons and holes. Ultimately, it evidently improved the efficiency of solar cells. This islikely to the local level at the bottom of the conduction band is formed with metal ion doping and the newaccepter level at the top of the valence band is formed with nonmetallic elements doping. The synergiesbetween the two factors resulted in the improvement of the photoelectric properties.In the fourth chapter, we use a similar hydrothermal method to prepare Nb-doped titanium dioxidenanomaterials. We analyze the effects of the doping amount of Nb and the different reaction time on themorphology and structure of titanium dioxide. It can be observed that the morphology of Nb-dopedsamples is a truncated octahedron from SEM. Further, we analysed the crystal structure of the samplesusing XRD, and the results showed that titanium dioxide of rutile and anatase phases will existsimultaneously when the concentration of Nb-doped is relatively high. Further, the crystal structure of thesamples transformed from the rutile phase to the anatase phase with the increase of the concentration ofNb-doped. Then, the effect of different reaction time on the structure of Nb-doped titanium dioxide was investigated. The results indicated that the longer the reaction time is, the higher the anatase phase ratio inthe sample is. When the reaction time is6h, the crystal structure of the prepared samples was completelythe anatase phase.