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Preparation of Titanium Nanocrystals from Titanium (Ⅳ) Bis (Ammonium Lactato) Dihydroxide and Their Application in DSSCs

Author: HaoYanMing
Tutor: ZhangQingHong
School: Donghua University
Course: Materials Processing Engineering
Keywords: Dye-sensitized solar cells Titanium dioxide TALH Anatase Sol
CLC: TB383.1
Type: Master's thesis
Year: 2012
Downloads: 55
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Abstract

Dye-sensitized solar cells (DSSCs) as a kind of novel solar cells with low production cost, easy fabrication and high energy conversion effciency have became a hot topic in research field. As one of key factors that improve the DSSC performance, photoanode has attracted vast attention. Generally, the mainly used titanium precursors are titanium inorganic salts or titanium alkoxides such as titanium tetrachloride (TiCl4), titanium isopropoxide. For their high reactivity, considerable agglomerates will be generated after changing the temperature or the pH value. In addition, large amounts of inorganic ions will be released during the hydrolysis process, which can compress the electrical double layer of initial colloidal particles, and result to large percipitate particles generation. The hydrolysis of titanium alkoxides produces various alcohol which not only changes the dielectric constant of aqueous solution but also is selective adsorbed on crystal planes, and all these had a complex affect on the morphology of TiO2 nanoparticles. So all these factors will lead to some defects of the obtained nanocrystallites TiO2 such as serious agglomeration, the wide crystallite size distribution, small surface area and so on.Post-treatment is essential to improve the interface performance of photoanode. The common method is using TiCl4 aqueous solution to treat TiO2 film. But amounts of HCl would be released during the treatment process, and the HCl will corrode the Flourine-doped tin oxide (FTO) glass, which will prevent the further improvement of energy conversion efficiency. Scattering layer made from the large TiO2 particles is very crucial important to improve the performance of DSSCs due to their good scattering ability. But scattering film always hardly loads dye molecules for its specific surface area, which limits the improvement of DSSCs performance.In this study, some works have been done to solved these problems:(1) Titanium (IV) bis (ammonium lactato) dihydroxide (TALH) as low reactivity and water-soluble titania precursor was employed to synthesis different TiO2 nanocrystallines through the sol-gel method and directly hydrothermal treatment process under alkaline condition. Both two TiO2 nanocrystals were employed to assemble into DSSCs, and the energy conversion efficiency were 7.8% and 8.9%, respectively. Two kinds of different TiO2 nanocrystals were prepared by the hydrolysis-hydrothermal treatment process under acidic condition. Both two TiO2 nanocrystals were employed to assemble into DSSCs, and the energy conversion efficiency of 5.3% and 8.1% were obtained, respectively.(2) TALH was utilized to synthesize alkaline anatase TiO2 sol through the hydrolysis at 95℃for 24 h. The obtain anatase TiO2 sol was in good dispersity and stability. When the sol was used to treat the TiO2 photoanodes, it could improve the connectivity of TiO2 films and enhance the adhension between FTO and TiO2 nanoporous films. The eventually obtained photoanodes improved energy conversion efficiency of DSSCs from 8.1% to 9.3%.(3) For TALH with negatively charged, the large nanoparticles with the size of 400-500 nm was coated with a layer of small nanoparticles through electrostatic interaction between polyelectrolyte and TALH, The crystallite size of coated small nanoparticles was of ca.7 nm. The coated large TiO2 powders were used as a scattering layer of DSSCs to increase the energy conversion efficiency from 6.2% to 7.1%.

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