Research On The Multiferroic Materials Bi₅FeTi₃O₁₅ As Counter Electrodes In Dye Sensitized Solar Cells

With the rapid development of science and technology at present, energy shortage and environmental pollution are the most concerned topics all over the world. People are exploring new environment-friendly energy which mainly includes fuel ethanol, biofuels, wind and solar power. Solar energy is a kind of renewable, no pollution and new energy, gradually developed into scientific research hotspot. Solar cells are devices, from which photoelectric conversion can be achieved using solar energy, transferring solar light into electricity and outputting voltage and current. Dye-sensitized Solar Cells?DSSCs? rely on its simple preparation process, environment friendly, advantages of rich raw materials and good practical prospect, have received the world's attention since Ecole Polytechnique Federale de Lausanne M. Gr?tze professor had been a breakthrough for the preparation of DSSC in 1991.Bi₅FeTi₃O₁₅?BFTO? is one of the typical representatives of layered perovskite ferroelectric material, and it has unique 4 layers of perovskite structure, which is due to the BiFeO₃ perovskite materials?BFO? is inserted into the three layers of perovskite structure Bi₄Ti₃O₁₂?BTO?. So far, there have been many related research reports about the magnetic, ferroelectric and dielectric properties of BFTO. But the photovoltaic propertie of BFTO was not reported. In addition, the BFO and BTO have been reported as DSSCs electrode materials, and BFTO have no related reports. The purpose of this paper is preparing BFTO nanofibers through the electrostatic spinning and researching the performance of BFTO as Counter cells in dye-sensitised solar cells. The main research process as follows:Chapter 1 states how to prepare BFTO nanofibers by electrostatic spinning. The precursor solution we prepare contains Bi, Fe, Ti and O four elements. In addition, we use macromolecule organic matter polyvinylpyrrolidone?PVP? as thickener agent. Electrostatic spinning experiment is on a DC high voltage of about 8 14 kV, receiving distance of about 10 20 cm, solution advancing speed of about 5¹5 mu l/min. The nanofibers we get are calcined at 650 ? for 30 min in air in order to get good, uniform particle size and crystal form. Nanofibers are consisted of small crystal grains end-to-end, which diameters are about 40 100 nm. Then the physical characterization of BFTO nanofibers is by XRD, SEM, TEM and UV-vis.Chapter 2 introduces we adopt the layered structure and large surface area of molybdenum disulfide?MoS₂?, mixing with BFTO as the DSSCs electrode materials. The photovoltaic performance of composites improves because of the good conductivity and catalytic activity of MoS₂. By electrochemical workstation tests when BFTO/MoS2 complexes of MoS₂ mass ratio is 50%, the CE has the largest Jsc and Voc than others, and its photoelectric conversion efficiency is 5.20%, which is almost dozens of times larger than that of BFTO. The experimental results show that MoS2 can greatly improves conductivity and electric catalytic activity than BFTO as CE in DSSCs. MoS₂ also improves the large specific surface area of CE at the same time, eventually makes the photoelectric conversion efficiency improved.BFTO through compositing graphene, enhances own photoelectric conversion efficiency in Chapter 3. Graphene is one of the new carbon crystal family nanomaterials and it has a unique 2D structure. As graphene has good carrier mobility and good electrical conductivity, we mixed BFTO with graphene in the mortar grinded 2h. Then the CEs were fabricated by scraping film, annealing, and assembled into DSSCs. When the proportion of graphene accounted for 2%, the photoelectric conversion efficiency is close to the photoelectric conversion efficiency of Pt counter electrode. The results show that BFTO nanoparticles enclosed with the graphene, can improve the electric catalytic activity and conductive ability of composite materials through enough grinding. Because of the great specific surface area of graphene, the speed of I3—/ I— electronic reduction in electrolyte with the electrode can be improved, so as to speed up the reaction. Therefore graphene can improve BFTO photoelectric performance, and we can verify through electrochemical test.