Preparation And Photoelectric Properties Of Carbon-based Transition Metal Compound Catalytic Materials

As an important part of the latest generation solar cells,sensitized solar cell contains two major exploration direction:dye sensitized solar cells（DSSCs）and quantum dot sensitized solar cells（QDSSCs）.Distincted by the sensitization materials,DSSCs mainly apply dyes as sensitizers,while QDSSCs use quantum dots principally.They reveal full prospection to explore for the future development of energy conversion,in which few economic and resource is required,but efficient applied performance can be achieved,moreover accessing the sustainable development of environment friendly characteristics.In general,the main structures constituting a sensitized solar cell are a semiconductor membraniform photoanode（typically Ti O₂）,a sensitizer for photoanode sensitizing,an electrolyte portion（liquid or solid）that provides REDOX electrical pairs for reactions inside the cell,as well as a counter electrode（CE）for supporting electrocatalyst.Thereinto,counter electrode can promote the recycling of redox couple and collect external circuit electrons,which is essential for the successful operation of sensitized solar cells.For DSSCs,metal Pt electrode is widely used currently.However,not only the noble metal characteristics with heavy costing and infrequent natural reserves but also the corrosion effect with I^-/I₃^-redox couple greatly limit the long-term development and wide application of Pt as electrode material.For QDSSCs,Cu_xS is generally applied to be the typical counter electrode,while Cu_xS deposited on FTO or brass substrate may gradually be separated from CEs,causing pollution to the photoanode,leading to deterioration of photovoltaic performance,and limiting the improvement of the overall energy conversion efficiency of the battery.Therefore,it is a pivotal aspect for the prospective development of sensitized solar cells to explore and develop new and excellent counter electrode materials to replace the leading role of Pt and Cu_xS in the counter electrode materials.In recent years,transition metal compounds（TMCs）have shown great potential in the exploration of the counter electrode of sensitized solar cells on account of their high electro-catalysis peculiarity.However,the lacking ability to conduct electricity of pure transition element compounds impedes the development of their excellent electrochemical performance.Therefore,in this paper,the transition metal compounds and carbon materials are combined through two different composite methods to achieve the complementary combination of excellent electrochemical activity and good electrical conductivity,applying in the research of sensitized solar cell CEs to ulteriorly promote the optimization of the overall cell property of the solar cell:（1）CoFe₂O₄@C nanoparticle composites with hollow structure were successfully prepared by ultrasonic dissolution-vacuum evaporation-high-temperature sintering based on the principle of Kirkendall effect.Adjusting the concentration ratio of each metal salt in the precursor solution,the size of CoFe₂O₄@C nanoparticles was homogeneous and no agglomeration occurred.As a ternary transition metal oxide,the interaction and coordination between the two metal ions make the electrochemical activity of CoFe₂O₄prominent.Moreover,the deposition of a thin carbon shell outside can noteworthily boost the electrode stability and electrical conductivity of the overall structure,facilitating the successful combination of superior catalytic activity,conductivity and stability of CoFe₂O₄@C composite material.Without obvious agglomeration phenomenon,CoFe₂O₄@C shows a large specific surface area,pressenting superior electrocatalytic performance.Applied in the DSSCs counter electrode via spraying method,the performance of obtained DSSCs were optimised by controlling the spraying times to achieve different film thickness,eventually it shows an excellent photoelectric conversion efficiency of 7.80%,which significantly towers above the output of etching carbon electrode（6.36%）under the same conditions,and even better than that of Pt counter electrode（7.05%）.The composite can additionally catalyze the recycling of I^-/I₃^-redox couple steadily,which provides more possibilities for the study of Pt-free materials for DSSCs counter electrode.（2）With the metal organic framework ZIF-67 as carbon source and morphology template,Cu and Co nanoparticles were successfully doped into the ZIF-67 framework by hydrothermal-sedimentation synthesis and high-temperature sintering,and ultimately Cu/CO@NCF composite was prepared.Profiting from the superior specific surface area and porosity of ZIF-67,the mergence of copper and cobalt particles within the calcination was inhibited,contributing to an befitting interspersion of copper and cobalt nanoparticles in the nitrogen-incorporated carbon skeleton within the pyrolysis process.While the copper and cobalt particles play a good catalytic activity in the carbon skeleton,the coated carbon material realizes the synergistic enhancement of the overall electrical conductivity and stability,promoting the catalytic effect of composite materials to regenerate the S^2-/S_n^2-redox couple and getting a long-term application stably.The composite material was printed on the surface of FTO conductive glass by screen printing method to prepare counter electrode.To obtain the counter electrode elements with different film thickness,we controlled the number of printing layers,investigating the optimal thickness of composite as QDSSCs counter electrode.Lastly,the QDSSCs with Cu/Co@NCF composites electrode achieved excellent performance:a PCE of 6.66%,close to that of Cu₂S/Cu counter electrode（7.29%）,proving a more stable and excellent counter electrode material with the potential to be an alternative material for the CE application of quantum dot sensitized solar cells.