Preparation And Application Of Graphene-based Counter Electrode For Dye-sensitized Solar Cell

Nowadays,energy supply is an issue that needs to be addressed urgently for human society.As a result,it appears to be an efficient solution to develop renewable energies such as wind energy,tidal energy,geothermal energy and solar energy.As one of the cleanest and most abundant renewable energy sources,solar energy has great potential,and many studies focus on the dye-sensitized solar cells(DSSCs)due to their low cost,simple preparation process,high photoelectric conversion efficiency and wonderful stability.The conventional DSSCs generally consist of a dye-sensitized nanocrystalline TiO2 photoanode coated on fluorine doped tin oxide(FTO)glass,triiodide/iodide(I3-/I-)redox electrolyte,and a counter electrode(CE).The CE plays a key role in collecting electrons from external circuit and catalyzing the redox couple regeneration,where a steady power output can be achieved and well kept.Up to now,the noble metal platinum(Pt)is usually employed as an efficient CE for DSSCs.However,the large-scale utilization of Pt is restricted by several drawbacks like natural scarcity,high cost,and easily corroded by iodine-based electrolytes.In consequence,it is urgent to explore the low-cost and high efficient catalysts for the reduction of I3-.Carbon nanomaterials own unique physical and chemical properties,such as high specific surface area,high conductivity,high catalytic activity,and low cost.Therefore,they are possible candidates to replace the traditional platinum CEs in DSSCs.As the most promising carbon material,graphene(G)has attracted much attention owing to its excellent performance.In our work,graphene oxide(GO)induced fabrication of pillared and double-faced polyaniline arrays(PANI/GO)and crumpled/heteroatom doping graphene(CHDG)have been successfully synthesized.Their performance for catalyzing the reduction of I3-as CEs in DSSCs has been investigated and the main results are as follows:A kind of hierarchical nanocomposite of pillared and oriented PANI nanocone arrays induced by graphene oxide(GO)sheets were engineered through in-situ polymerization under low temperature.The GO adopted was used as the substrate and structure-directing agent to induce the nucleation and assembly of PANI nanorod arrays.Abundant oxygen-containing function groups on the GO surface acted as the anchoring sites for inducing nucleation and growth of the PANI seeds.The PANI/GO CE delivers a better electrocatalytic activity towards the reduction of I3-in comparison to that of commercial Pt and pure PANI CEs owing to the changes of PANI's morphology.A high conversion efficiency of 8.19 ± 0.08% can be achieved when the mass ratio of aniline to GO is 10:1.CHDG was synthesized using hydrothermal method followed by thermal annealing approach,in which GO and thiourea were employed as sources of doped elements like N and S,respectively,and the polystyrene(PS)sphere as template.During the hydrothermal process,PS sphere was fully contacted and squeezed with GO slice,then graphene gel(G)formed and crumples came out.After thermal annealing process,G got further reduction and N,S atoms were incorporated into G matrix successfully through the pyrolysis of thiourea.When the CHDG is applied as CE for DSSC,it shows a remarkable catalytic activity compared with that of G and Pt.The DSSC assembled with CHDG CE delivered a conversion efficiency of 8.32 ± 0.09 % and superior electrochemical stability.