Synthesis and characterization of mesoporous silica/titania nanocomposites : potential additives for dye sensitized solar cells (DSSCs)

M.Sc. (Nanoscience)Abstract: The photoanode is an important part of the DSSCs as it is the medium for dye adsorption, electron transport and electrolyte diffusion. The composition and morphology of the photoanode therefore directly influences the performance of the cell. Optimising the morphology of the photoanode is therefore one of the key factors in improving the performance of the DSSCs. This work entailed the synthesis of titania supported on silica nanocomposites for use as light scattering materials in the photoanode with the motivation of optimising the morphology of the photoanode and further enhance the energy conversion efficiency of the DSSCs. The silica support materials, specifically mesoporous silica, SBA-15 and non-mesoporous SiO2 were synthesized through the soft-template acid catalyzed sol-gel method and base catalyzed sol-gel method respectively. Two SBA-15 nanomaterials were synthesized by varying the hydrolysis and aging times which resulted in materials of different textural and morphological properties. These silica support materials (SiO2, SBA-15 A1 and SBA-15 A2) were used as support materials for the synthesis of TiO2 supported on silica nanocomposites. Also, TiO2 nanoparticles of size 19.32 ±3.70 nm (n = 193) were synthesized for use as active site of the photoanode. The physical, chemical and optical properties of the nanoparticles and nanocomposites were studied using FTIR, TEM, Nitrogen Sorption, SEM-EDS, XRD, and diffuse reflectance Ultraviolet-Visible (DR-UV-VIS) spectroscopy. The nitrogen desorption results of the 10 wt% TiO2 / SBA-15 nanocomposites just like the parent SBA-15 support, revealed the Type IV isotherms with H1 hysteresis loops which indicated that the support materials did not lose their mesoporosity and uniform pore size arrangement upon incorporation of TiO2 nanocrystals. This finding was supported by the TEM results. The energy band gaps of TiO2 supported on the mesoporous silica (SBA-15) (3.60 eV) were blue shifted relative to the unsupported TiO2 (3.44 eV) and TiO2 supported on the non-mesoporous SiO2 (3.55 eV). These results confirmed the XRD results which indicated smaller TiO2 crystallite sizes for TiO2 crystals supported on the SBA-15 support materials which were 10.60 nm as compared to the unsupported TiO2 and TiO2 supported on the non-mesoporous SiO2 (15.89 nm). The band gap increased as the crystallite sizes decreased..