Preparation Of Counter Electrode For Dye Sensitized Solar Cells Based On Metal-Organic Framework Materials

As an emerging new energy device,dye-sensitized solar cells（DSSCs）not only have excellent photoelectric conversion efficiency,but also have a wide range of raw materials,low manufacturing cost,simple production process,and clean and non-polluting preparation,which is highly concerned by researchers.The counter electrode（CE）,as an important component of DSSCs,plays an important role in catalyzing the recycling of redox electrolytes and collecting electrons from external circuits.Platinum（Pt）as a traditional CE material also has many shortcomings.As a rare metal,Pt has an expensive price and is easily passivated by electrolyte corrosion,which seriously hinders the commercial development of DSSCs.Therefore,the development of stable,efficient and low-cost CE materials is of great significance for the large-scale production of DSSCs.Metal organic framework compounds（MOFs）have large specific surface area,high porosity,tunable nanostructures and abundant unsaturated sites,which are in perfect conformity with the requirements for developing DSSCs CE materials.This makes MOFs have great potential in developing stable,efficient and low-cost DSSCs.In this paper,based on MOFs and their derivatives,composite materials with special structure were designed and synthesized as stable,high-efficiency and low-cost non-Pt CE materials,and applied to DSSCs.The material was characterized by a series of physical tests,and the catalytic and photoelectric properties of the material were analyzed by electrochemical tests.（1）Firstly,a simple chemical reaction was used to synthesize a Co-based MOFs material ZIF-67 with a rhombohedral 12-member structure.The composite material MoS₂@Co₃S₄with a hollow 12-faced Co₃S₄ loaded MoS₂ nanosheet structure was then synthesized by a two-step hydrothermal method.The loading of the MoS₂ nanosheets was adjusted by changing the amount of Mo source during synthesis.The structural morphology and chemical composition of the composites were demonstrated by a number of physical tests.And they were applied to DSSCs CE and electrochemical tests were carried out to analyze the electrochemical and photoelectric properties of the composites.The results show that CE prepared based on MoS₂@Co₃S₄-0.5 has excellent catalytic performance and exhibits a photoelectric conversion efficiency（PCE）of 7.86%,which is superior to PCE measured by Pt CE under the same conditions.This indicates that there is a good potential for the preparation of metal sulfide composites based on MOFs in DSSCs CE studies.（2）Using cobalt nitrate and dimethylimidazole as raw materials and deionized water as solvent to synthesize a fusiform MOFs derivative material Co-MOF as a precursor.Porous N-doped carbon（CN）loaded Co nanoparticle composites（Co@CN）were prepared by calcination method,and CN loaded CoNi alloy composites（CoNi@CN）were prepared by ion-exchanged Ni-doping,which in order to improve the catalytic performance of the composite.The composite materials were applied to DSSCs and electrochemically tested.The results show that the catalytic properties of the materials are further improved after the incorporation of Ni metal,and PCE reaches 8.85%,which is significantly higher than Pt CE.The analysis shows that the preparation of CN as a carrier based on MOFs and its derivative materials is an effective means to develop high-efficiency and low-cost CE materials,and the metal alloys help to improve the catalytic performance of the materials.（3）Through the exploration of the former two materials,CN supported metal sulfide composites were designed as CE catalytic materials,and the materials were successfully synthesized and structurally characterized by physical means.CN loaded Co₉S₈ and Ni₉S₈composites（Co₉S₈/Ni₉S₈@C-N）were prepared by calcination and ion exchange treatment followed by hydrothermal vulcanization with thioacetamide.The electrochemical properties of the materials were tested by applying Co₉S₈/Ni₉S₈@C-N to DSSCs CE.The results show that Co₉S₈/Ni₉S₈@C-N exhibits excellent electrocatalytic performance.In the photoelectric performance test,8.91%of PCE was much higher than Pt CE’s PCE（7.58%）.It can be seen that the preparation of CN supported sulfide composites based on MOFs materials and their derivatives is a promising idea for high-efficiency and low-cost DSSCs CE materials.In summary,this paper designs and synthesizes a variety of composite catalytic materials with special structures and functions based on MOFs and its derivatives,and applies them as CE materials to DSSCs to study their catalytic and photoelectric properties.The introduction of MOFs materials into the development of DSSCs CE not only expands the material source of CE,but also reduces the production cost of DSSCs.At the same time,it is very good to develop a more stable and efficient CE based on the characteristics of MOFs.