Study On Preparation Of Platinum-free Counter Electrode Materials And Their Electrocatalytic Performance

Dye-sensitized solar cells（DSSCs）are the third-generation solar cells which have drawn worldwide attention because of their simple assembly procedure,low cost,environmental friendliness and high-power conversion efficiency（PCE）.Though dye-sensitized solar cells have these advantages,there are still many difficulties to conquer,such as the photoelectric conversion efficiency and the cost of DSSCs.So,a lot of works are needed to optimize the dyes,redox electrolytes,counter electrodes and photoanodes.The counter electrode（CE）is a key component of DSSCs to collect the electrons from the external circuit.Counter electrode also acts as a catalyst for the redox couples regeneration.So far,the most commonly used material in the CE is a thin layer of platinum（Pt）.Pt has been proved as an excellent CE catalyst because of its high activity and stability,which have already become a reference CE in the development of new CE catalyst.However,Pt metal is expensive and low abundance in nature.The high cost prevents Pt meeting the increasing demand for large-scale manufacturing.To reduce the cost of the CE,considerable efforts have been made to prepare low cost Pt-free materials,such as carbon-based materials,metal oxides,metal sulfides,metal nitrides and metal carbides conjugated polymers,etc.But low-cost materials and sample fabrication techniques are always favored for widespread DSSCs.Therefore,it still needs extensive efforts to improve the catalyst activity,reduce the costs and increase the stability of CE to meet the practical application of DSSCs.The third chapter reports a simple,low cost and effective method to synthesize carbon modified TiO₂ counter electrodes for high-efficiency DSSCs,by annealing the screen-printing TiO₂ paste with organic compound under vacuum.When used as a counter electrode of DSSCs,the photoelectric conversion efficiency of DSSCs（450℃,5.42%）is similar to that of the referenced Pt counter electrode（5.84%）.For TiO₂/C is one of the cheapest and stable materials,this work presents a truly simple,low cost method to produce CE on a largescale for high efficient dye-sensitized solar cells.The fourth chapter introduces the application of graphene/TiO₂ composite materials in the counter electrode of dye-sensitized solar cells.In order to prepare the graphene/TiO₂ composite material counter electrode,we mixed graphene and TiO₂paste in different proportions,then screen printed on FTO and dried.The DSSCs was assembled and tested.The experimental results proved that the photoelectric conversion efficiency of this counter electrode（10 wt%,5.74%）was comparable to the Pt counter electrode.The results prove that graphene has sufficient electrocatalytic potential for the counter electrode.Compared with common graphene-base counter electrode,the 10%ratio can still support the efficient catalysis of the DSSCs.The composite materials have simple preparation process,great catalytic performance and low cost,so it is suitable for large-scale application of dye-sensitized solar cells.Chapter five introduces the efficiency change of DSSCs caused by different amounts of Mo S₂ on the counter electrode.Through the pretreatment of FTO,the surface of FTO obtains super-hydrophilic properties,which can make the liquid film spread evenly on its surface.Then drop different concentrations of ammonium molybdate solution on the treated FTO to control the Mo atom concentration on the FTO surface.After reacting with sulfur,counter electrodes with different amounts of Mo S₂ are formed and assembled into DSSCs.The result shows that within a certain range,the efficiency of DSSCs does not decrease proportionally with the decrease of the amount of Mo S₂ on the counter electrode.This result indicates that a small amount of Mo S₂ is sufficient to provide high efficiency and demonstrating that the Mo S₂counter electrodes have a greater electrocatalytic potential.This research provides a new exploration direction and feasible experimental methods for fully exploring the potential of the counter electrode,improving the efficiency and saving manufacturing costs of DSSCs.