Preparation Of TiO₂-based Porous Microspheres And Their Application In Dye-sensitized Solar Cells

As one of the representatives of the third generation thin film solar cells,dye-sensitized solar cells?DSSCs?have many advantages,such as low cost,simple assembly,relatively high power conversion efficiency and so on.It has the promising future in large scale production and industrial application.As one of the choices of DSSCs photoanode materials,titanium dioxide has been widely used in photoanode due to its advantages of non-pollution,low cost,wide band gap,good electrochemical stability and good photoelectric effect.However,in order to make DSSCs achieve the desired high powder conversion efficiency,the further optimization of the photoanode is still a challenge.In recent years,more and more composite photoanodes composed of titanium dioxide nano-materials with different dimensions have been designed.Large-sized titanium dioxide mesoporous spheres are favored because of their high specific surface area and excellent light scattering properties.The composite photoanodes made by using titanium dioxide mesoporous spheres as scattering layer and traditional titanium dioxide nanoparticles as transparent layer,which often possesses high electron transfer rate as well as enhanced dye-loading.Therefore,this theis mainly focuses on the preparation of titanium dioxide-based mesoporous microspheres,and the application and performance optimization of DSSCs.The main work and innovative results are as follows:1.Template-free preparation and photoelectric properties of titanium dioxide hollow spheres:titanium dioxide hollow spheres are fabricated via a facile and efficient approach which avoids the use of templates.Titanium dioxide hollow spheres show superior light trapping characteristics and significantly improve the light-harvesting capability of the solar cells.The inside-out Ostwald ripening mechanism interprets the formation of the hollow structure.The as-prepared titanium dioxide hollow spheres with diameters ranging from 1 to 1.5?m and a shell thickness of 150 nm are formed by the self-assembly of nanoparticles with a size of about12 nm.The mesoporous titanium dioxide hollow spheres with a high specific surface area up to166.2 m² g^-1 and excellent light harvesting ability can be used as an ideal light scattering layer.A double layered photoanode made of as-prepared titanium dioxide hollow spheres as the overlayer and P25 as the bottom layer for DSSC achieved a high power conversion efficiency of 7.90%,which is 31.7%higher than that of DSSC for P25 photocathode.2.Mesoporous titanium dioxide core-shell structural spheres?TiO₂-CSSs?featuring excellent light scattering property and high specific surface area are synthesized via a facile hydrothermal method.The most suitable reaction time and formation mechanism were explored.The results showed that anatase TiO₂-CSSs are obtained at 120°C for 6 h,and the formation of core-shell structure is interpreted by a typical asymmetric Ostwald ripening mechanism.DSSC is fabricated by using TiO₂-CSSs as the light scattering layer and the anatase TiO₂nanocrystallines as bottom layer.The power conversion efficiency of DSSC is up to 9.24%,which is due to the enhancing light scattering effect and increasing amount of dye loading.Furthermore,a small number of TiO₂ nanotubes are introduced to form the composited bottom layer.Consequently,this DSSC based on composite photoanode possesses superior electron transfer and high surface area,leading to an outstanding power conversion efficiency of 9.60%.3.The TiO₂/SnO₂ composite hollow spheres were prepared by template-assisted method.The diameters of composite hollow spheres are 1.5-4 um,the specific surface area is 92.9 m²/g,and the composite hollow spheres have excellent light scattering property.The power conversion efficiency of DSSC with composite hollow spheres photoanode is 7.72%,which is higher than that of DSSC with SnO₂ photoanode?2.70%?and DSSC with TiO₂ photoanode?6.26%?.Furthermore,a bilayer structure of photoanode was designed with anatase TiO₂nanocrystals as the bottom layer and TiO₂/SnO₂ composite hollow spheres as the light scattering layer,and the DSSC fabricated by using the bilayer photoanode showed an increased power conversion efficiency of 8.43%.