Cobalt-based Sulfide And Its Graphene Composites Were Designed And Synthesized To Study The Performance Of The Counter Electrode Of Dye-sensitized Solar Cells

Dye-sensitized solar cells?DSSCs?have attracted immense attention due to their relatively high conversion efficiency,low-cost and easy fabrication that compared with the traditional silicon solar cells.Generally,DSSCs have a sandwich structure with a photoanode comprising TiO2 sensitized by dye molecules?such as N719?,an electrolyte containing the redox couple of iodide/triiodide?I-/I3-?,and a counter elcetrode?CE?catalyzing the reduction of I3-to I-.Among them,the CE is a crucial component for achieving high performance which performs two critical functions: it collects the electrons flowing from the external circuit and catalyzes the reduction of I3-to I-.Currently,Pt is usually used as a standard CE due to its excellent catalytic activity and high electrical conductivity.However,the scarce Pt sources would lead to high cost in DSSCs.Moreover,Pt could dissolve in electrolyte and generate by-products such as PtI4 and H2PtI6 because of the corrosive I-/I3-redox electrolyte,which may deteriorate the long term stability of devices.Therefore,it is vital to develop low-cost and high performance CE materials for DSSCs.This thesis mainly focuses on the design and synthesis of metal sulfide as electocatalysts for highly efficient DSSCs,and some innovative results have been achieved,which is summarized as follow:?1?3D Co-Al-LDHs composed of ultrathin nanosheets were syntheisized via a simple hydrothermal method in a mixed solvent system,and then vulcanized with Na2 S to obtain the amorphous cobalt sulfide?CoS_x?which have a nanosheets structure.The as-prepared CoS_x dispersed into ethanol to form a slury,and then coated onto the FTO substrates using a doctor blade method to fabricate CoS_x CE.The CE exhibited efficient electrocatalytic activity in the reduction of I3-to I-in DSSCs.Moreover,the devices with CoS_x CE showed better stability and higher PCE compared with Pt CE in iodine based electrolyte.Meanwhile,we obtain a composite materials CoS_x/rGO by the same method.To fabricate CoS_x/rGO CE and exhibited efficient electrocatalytic activity.The devices with CoS_x/rGO CE showed better stability and higher PCE compared with Pt CE in iodine based electrolyte.?2?On the basis of cobalt sulfide,another transition metal cation was introduced to synthesize cobalt-based ternary sulfide.The CoFeS₂ nanorods and the CoFeS₂/rGO multilayers composed of Co-Fe-LDHs were prepared by hydrothermal method and co-vulcanized as precursors.The as-prepared Co FeS₂ and CoFeS₂/rGO dispersed into ethanol to form a slury,and then coated onto the FTO substrates using a doctor blade method to fabricate CoFeS₂ and CoFeS₂/rGO CEs,respectively.