Investigation Of Electrode Materials Of Dye-sensitized Solar Cells

At present, with the rapid development of human civilization, the global demand for energy is on a rapid increase. In order to satisfy the human need for energy, finding the low production cost, environment-friendly energy production mode has got more and more focuses. Since professor M. Gr?tzel successfully excogitated new concept of cell（Dye-sensitized Solar Cells, DSSCs） in 1991. DSSCs have attracted worldwide research attention, due to its features such as low manufacturing cost, simple production process, and environment-friendly.Typical DSSCs are usually consisted of N-type semiconductor oxides attached with dye molecules, electrolyte containing I- and I3-, and Pt counter electrode. Currently, people widely use Pt as the counter electrode material due to its excellent redox properties and electric conductivity. However, Pt is a very rare metal, expensive, and is not beneficial to the large-scale commercial application of DSSCs. So seeking for low-cost, abundant raw materials of counter electrodes has become an imminent task. Beside, when replacing Pt counter electrode with P-type semiconductor oxide as cathode materials to form series cells, which can further improve the Voc of cells, is a valid method of increasing the efficiency of solar cells. Therefore, the research on applications of P-type semiconductor oxide film in DSSCs has an important scientific impact.We found that NiCo₂O₄ is a P-type semiconductor oxide, which has a suitable valence band position and fast carrier migration rate in DSSCs. Hence, this thesis firstly explores the performances of different morphologies of NiCo₂O₄ in DSSCs. Based on the above work, this thesis also systematically explores the application of ternary transition metal sulphides Ni Co2S4 and CoNi₂S₄ as counter electrodes in DSSCs, and further investigates C/CoNi₂S₄ composite materials in the application of counter electrode in combination with electrostatic spinning technique. This theis mainly contains the following sections:First, we describe the development, structure and working principle of DSSCs briefly, and then discusses about the significance of the selected topics and the main research content of this thesis.Second, NiCo₂O₄ nanowires and nanosheets films were in-situ grown on the transparent conductive substrate（FTO） via a hydrothermal reaction. We can synthesize NiCo₂O₄ hierarchical structures with nanowires intertwined in nanosheets by two-step process. Tests found that the open circuit voltage and short circuit current of this NiCo₂O₄ hierarchical structure in DSSCs is 0.189 V and 8.35 m A/cm2, respectively, and the photoelectric conversion efficiency reaches 0.785%, which is much higher than traditional P-type semiconductor oxide Ni O.Third, based on the second section’s work, the Ni Co2S4 nanosheets films were synthesised via a direct anion exchange reaction with NiCo₂O₄ nanosheets films. Replacing Pt as the counter electrode of P-type NiCo₂O₄ nanosheet anode, the photoelectric conversion efficiency can reach 0.248%, higher than that（0.158%） of the Pt under the same measurement condition.Forth, CoNi₂S₄ nanoparticles films were grown on FTO directly via a hydrothermal method. We can change the thickness of the films by adjusting the reaction’s time. At the reaction time of 90 min, the efficiency of CoNi₂S₄ as counter electrode is the highest and can be 4.61%, which is comparable with that（4.67%） of the Pt under the same measurement condition.Fifth, we investigated the application of CoNi₂S₄ grown on C fiber composite materials as counter electrode. The efficiency of C/CoNi₂S₄ as counter electrode is 4.46%, close to that（5.34%） of the Pt. It still needs to optimize the composition and structure of composite materials for higher efficiency in the future.Finally, we give a summary of this thesis.