Preparation Of Dye-sensitized Solar Cells Based On Different Substrates And Optimization Of Their Structures And Performances

Dye-sensitized solar cells (DSSC) have attracted much attention due to their relatively low cost and high conversion efficiency;however, the traditionally used conductive glass substrates limit their applications because of rigid and heavy properties. Therefore, it is a key issue to prepare photoanodes of DSSC on flexible and light-weight substrates. On the other hand, TiO2nanoparticles and Ru-bipyridine dye, which are mostly used in DSSC, have low light-harvesting and narrow spectral response. Increasing light-harvesting efficiency and broadening spectral response are also important for the improvement of DSSC. Thus, we carried out investigation into fabrication of the photoanodes of DSSC on different flexible substrates, and increasing light-harvesting efficiency and broadening spectral response of the photoanodes. The main contents and conclusion are as follows:1. Flexible DSSCs are prepared on ITO-PET at low temperature (120℃) by adding TBOT and nanoglue to P25paste.(1) The amount of TBOT added to P25paste is critical for the performance of flexible DSSC. The nanoparticle interconnections will be enhanced with increasing amount of TBOT. After optimization, when mass ratio of TBOT/P25in the paste is0.17, the electrode has the best performance and an efficiency of3.94%is obtained.(2) Small TiO2nanoparticles (diameter<10nm) derived from non-hydrothermal method can enhance P25interconnection, increase dye absorption, decrease the pore size and the rate of electrolyte diffusion in the film. After optimization the small TiO2nanoparticles should be29wt%in the film, and efficiencis of3.53%and2.71%are obtained on FTO glass and ITO-PET substrates respectively. The above two preparations of binder-free P25paste have merits of simpleness, low-cost, good particle interconnections and relatively high efficiency. It is expected these methods can provide new routes for large-scale DSSCs based on plastic substrates.2Flexible DSSCs is prepared on ITO-PET at low temperature (150℃) by using sea urchin-like hierarchical TiO2microspheres as the paste and a novel iodine-free, quasi-solid state electrolyte based on ionic liquid DMPII.(1) Sea urchin-like hierarchical TiO2spheres, which are composed of TiO2nanoparticles and nanoribbons with high surface area (～97m2g-1) and good particle interconnection, are prepared by solvothermal method.(2) The TiO2spheres can supply sufficient area for dye absorption and reduce electron recombination, and the micro-pores in the film are favorable for the diffusion of quasi-solid state electrolyte. The TiO2spheres based flexible DSSC achieves efficiency of4.32%, which is better than P25nanoparticles based one.3. TiO2nanotube film is prepared on the surface of Ti foil by combining hydrothermal and transfer methods.(1) The diameter of TiO2nanotubes is less than10nm, and the nanotubes are tangled to form a porous film with thickness of～12μm. TiO2nanotube/Ti flexible photoanode is fabricated by transferring method.(2) The synthesized TiO2nanotubes can not only supply sufficient area for dye absorption, but also reduce electron recombination due to one-dimensional nanostructure. TiO2nanotube/Ti electrode obtains an efficiency of6.23%, which is higher than P25/Ti electrode. The above results can offer a reference for preparation of metal based DSSCs with high performance.4. Quasi-solid state DSSC on Ni/paper substrate is fabricated using binder-free TiO2paste and iodine-free quasi-solid state electrolyte.(1) Conductive Ni naoparticle layer is coated on flexible paper substrate by a simple solution deposition method.The sheet resistance of prepared Ni/paper substrate is lower (<1Ω sq-1), which is favorable for decrease of serial resistance of DSSC.(2) Small TiO2nanoparticles (diameter～9nm) are synthesized by hydrothermal method, and added to binder-free P25paste. The binder-free paste and iodine-free quasi-solid electrolyte can make good nanoparticle interconnections and avoid corrosion to the paper substrate. After250℃heat treatment, an efficiency of2.90%can be obtained by the Ni/paper based DSSC. The application of paper in DSSC can lower the cost of the cell significantly with maintaining the flexibility. It is important for broadening the area of DSSC application and the relative large scale production.5. To increase the light harvesting efficiency of DSSCs, some novel scattering materials are prepared.(I) One dimensional fusiform TIO2nanorods with width of20-80nm, length of200-400nm can be obtained by hydrothermal method. Three dimensional ZnO micro-flowers with diameter of-300nm, which are composed of pencil-like ZnO nanorods with length of～3μm,are synthesized and solution deposition method.(2) Due to the large size, TiO2nanorods have strong scattering effect and can increase the optical path in the film, leading to the enhancement of light-harvesting efficiency. And the one dimensional structure of TiO2nanorods can offer a direct path for the electron transfer, decrease electron recombination.However, adding TiO2nanorods will result in the decrease of surface area and dye absorption. After optimization, TiO2nanorods should be10wt%in the film electrode, and4.68%efficiency can be achieved, which is66.5%higher than that of electrode without TiO2nanorods.(3) ZnO micro-flowers are coated on ZnO nanoparticle film electrode and used as scattering layer for the DSSC. Because of the scattering effect of ZnO micro-flowers, the light absorption and light-harvesting efficiency of ZnO electrode increase significantly. The overall conversion efficiency of ZnO electrode is enhanced from2.32%to3.18%. I he above one and three dimensional nano-semiconductors can give more options of scattering materials for DSSCs.6. To expand the spectral response of DSSCs, TiO2film on FTO-glass substrate is cosensitized by stepwise method using metal-free organic dye DH-44and zine phthalocyaninc dye Zn-tri-PcNc-1.(1) Due to the matched spectral response of these two dyes, the spectral response of cosensitized photoanode is broadened, resulting in increased light-harvesting and conversion efficiency.(2) The cosensitized elctrode obtains an efficiency of6.61%with expanding the spectral response to near-infrared region, which is higher than the single dye DH-44sensitized one (5.16%) and Zn-tri-PcNc-1sensitized one (2.38%), showing significant advantages of cosensitization. This research offers a new route to prepare DSSCs with broad spectral response, low-cost and high efficiency.