Fabrication and Characterization of Exfoliated Montmorillonite/Titanium Dioxide Nanocomposites and Their Application on Solid-State Dye Sensitized Solar Cell

A novel method using the soap-free emulsion polymerization to exfoliate mortmorillonite (MMT) was discovered by our laboratory. We found that sunscreen with the addition of exfoliated MMT (exMMT) can protect skin from getting oxidized. By using exMMT to gel the ionic liquid electrolyte for dye sensitized solar cell (DSSC), I- was oxidized to I3- and I5- improving the charge transportation. As a result, to investigate the properties of exMMT associated with the attraction of photoelectrons was the main objective of this master thesis. Also, exMMT was farbricated by exfoliating MMT with a kind of amine-terminated polymer in order to compare the results with soap-free emulsion polymerization method. TEM images indicated that the size of exMMT was ~300 nm in width. Because exMMT has a strong affinity for amine group, FTIR was used to analyze the adsorption of amino acid by exMMT. The results showed that the peak of –NH3+ was observed for the samples with exMMT prepared by the anionic method, but not by the cationic method which had the same –NH3+ functional group; however, the peak of –COOH exhibited the opposite result which was found for the exMMT prepared by the cationic method, but not by the anionic method. Next, from the TEM image, we found that TiO2 nanoparticles were successfully adsorbed on exMMT/amino acid to form an exMMT/TiO2 composite with aid of –COOH functional groups, which were further comfirmed by EDS measurement and X-ray diffraction pattern. After that, methyl blue solution with exMMT/TiO2 composites was exposed to ultraviolet lamp for different time. These PL and UV-vis spectra of methyl blue demonstrated that composite could hindered photodegradation reaction due to that exMMT has strong affinity to the photoelectrons produced by TiO2. In the last part, the performance of solid-state dye sensitized solar cell (SSDSSC) with exMMT/TiO2 composite layers inserting at different location of TiO2 photoelectrode were investigated. The results showed that composites located on the top of porous TiO2 layer or dense TiO¬2 layer within TiO2 photoelectrode had higher Voc and longer τIMVS due to the increase of energy band gap ; whereas one layer of composites deposited on top of the FTO glass within TiO2 photoelectrode exhibited higher Jsc and shorter τIMPS. It could be deduced that electrons attracted by composites were easier to transport into FTO conducting glass. Therefore, the power conversion efficiency increased from 0.691 ± 0.035 % to 0.719 ± 0.046 %. Besides, electrochemical impedance spectroscopy (EIS) results showed that the impedance decreased under sunlight but increased in the dark, suggesting that composites could rectify the electrons.