Fabrication And Optical Properties Study Of Photonic Crystals Used For Dye-sensitized Solar Cells

In recent years, photonic crystals have attracted widespread attention. Because photonic crystals may be is one of effective methods to solve integration issues of photonic device. Many studies have been focused on the basic issues during the fabrication process of colloidal crystals assembled from colloidal spheres. For example, the defects control of colloidal crystals, the tune of optical stop band, and so on. The colloidal crystals maybe have a potential application in the dye-sensitized solar cells (DSSCs), because of photonic bandgap of colloidal crystals. In our work, the fabrication of ultra-thickness and crack-free colloidal crystals, the tune of optical stop bands of different colloidal crystals, and the application of colloidal crystals in DSSCs are systematically studied, respectively. A series of original and innovative results have been also obtained, and described as follows.Firstly, the crack-free colloidal crystals composed of sintered silica spheres are fabricated by an isothermal heating evaporation induced self-assembly method. Ultra-thick and crack-free colloidal crystals with100μm in thickness are also fabricated by a crystalline layer assembly technique. The effect of sintering process on silica spheres fabricated by the modified Stober method is studied. There are no crack defects on the surface and cross-sectional of colloidal crystals of sintered silica spheres. In the reflection spectra, the experiment values of the optical stop band wavelength agree well with theorical values calculated by the Bragg’s law. The interface between two crystalline layers of ultra-thick and crack-free colloidal crystals has a good adhesion. The intensity of reflection peaks increases with increase of the thickness of colloidal crystals.Secondly, colloidal crystals composed of monodisperse polystyrene/silica core-shell (PS@SiO2) spheres are fabricated by an isothermal vertical deposition methd. Silica shell colloidal crystals are obtained by sintering the colloidal crystals of PS@SiO2 spheres. The transmission spectra of silica shell colloidal crystals show that there is a red shift of optical stop band with increasing the inner diameter and the shell thickness of hollow silica spheres. The dual-tuned of optical stop bands have been achieved by controlling the diameter and the effective refractive index of hollow silica spheres. Based on a crystalline layer assembly technique, colloidal crystal heterostructures formed from PS@SiO2spheres are fabricated. Colloidal crystal heterostructures formed from hollow silica spheres are also obtained by sintering the colloidal crystal heterostructures. Under the assumption that incident light is oriented perpendicular to the surface of colloidal crystal heterostructures, there are two independent optical stop bands, which is a simple superposition of optical stop bands of the two crystalline layers.Thirdly, the application of titania inverse opal (TiO210) in DSSCs is studied. Compared with a reference DSSC with P25film, the DSSCs with P25-TiO210films exhibits the much higher short-circuit current density, open-circuit voltage, and photoelectric conversion efficiency. Then the effect of silica/gold core-shell spheres (SiO2@Au) on performance of DSSCs is also studied. The results show that the power conversion efficiency of the DSSCs doped with P25-SiO2@Au spheres films (SiO2of SiO2@Au spheres:P25=0.05%) is greatly improved. Based on the above, the composite TiO2films of P25-SiO2@Au spheres-TiO210are fabricated. Compared with a DSSC with P25film, the short-circuit current density of the DSSCs with the composite TiO2films is improved from9.08mA/cm2to14.37mA/cm2. The open-circuit voltage is improved from0.65V to0.67V. And the power conversion efficiency is also improved from3.95%to6.35%.