Study On Nano/Microstructure Carbon-based Counter Electrode For Dye-Sensitized Solar Cells

Dye-sensitized solar cells(DSSCs)are composed of dye-sensitized nanocrystalline Ti O2 photoanodes,electrolyte containing triiodide/iodide(I3-/I-)redox couple,and counter electrode(CE).They have been regarded as a valid alternative for next-generation photovoltaic devices on account of their low manufacture costs,modifiable transparency features,and relatively high power conversion efficiencies(PCE).The CE acting as a catalyst to reduce the redox couples and a mediator to regenerate the sensitizer after electron injection is a key part.However,the traditional and acceptable Platinum(Pt)CE,which is high cost,resource-limited and electrochemically instability,restricts the large-scale practical use of DSSCs.As such,the designing of low cost and high performance catalysts to replace Pt for the reduction of I3-is one of mainly focused directions.Carbon materials have been widely used in DSSCs due to their various kinds,high conductivity,good electrochemical stability,and low cost.They are mainly divided into two categories,one is nanometer-sized carbon materials,including graphene,carbon nanotubes and so on,the other is micrometer-sized carbon materials,including graphite,activated carbon and so on.In our work,two size of carbon materials were prepared,one is nanometer-sized Co S1.097 compounding nitrogen-doped carbon(Co S/ZNCA),the other is micrometer-sized carbon molecular sieves(CMS).The corresponding photovoltaic and electrochemical performance was investigated in detail and the main results are as follows:The Co S1.097 nanoballs compounding nitrogen-doped carbon(Co S/ZNCA)were engineered through in-situ chemical conversion process,the precursors were Co-based metal organic framework(ZIF-67),the cobalt ions produced after the acid leaching were used directly as one of the precursors to be transformed into cobalt sulfides and in-situ grow on the surface of conductive carbon matrix,thus achieving a green and environment friendliness process.When applied as counter electrode(CE)for triiodide reduction in scalable DSSCs,the Co S/ZNCA hybrids exhibit a high power conversion efficiency(PCE)of 8.54%,outperforming the Pt reference(6.53%).The significantly improved electrocatalytic activity towards the triiodide reduction is contributed by the highly electroactive Co S1.097 species and N-doping carbon functioning as conductive matrix.In addition,the as-made Co S/ZNCA CE also shows an outstanding electrochemical stability.CMS have been employed as the CE materials for the first time and possess excellent electrocatalytic activity towards the I3-/I-redox reaction,compared to multi-walled carbon nanotube(MWCNT),activated carbon(AC),reduced graphene oxide(RGO).The high performance of CMS is ascribed to its superior electrical conductivity and catalytic activity.Besides,CMS800 was prepared by thermal annealing of CMS electrode at 800℃.when applied as CE for the DSSCs,it achieved a higher conversion efficiency of 8.56%,outerperforming the Pt CE.The significantly improved performance was benefiting from the enhanced conductivity,which was due to the increase of the graphitization for CMS.Moreover,the CMS800 CE also exhibited an outstanding electrochemical stability.