CoS-graphene Composite Counter Electrode And Its Photovoltaic Properties

Dye-sensitized solar cell (DSSC) has appeared as a promising device for nextgeneration photovoltaic devices among solar cells because of their reasonable conversionefficiency and low-cost fabrication. The counter electrode (CE) is one of the mostimportant components in DSSC and platinum is the most widely used counter electrodematerial up to now. However, Pt is a precious metal, and the resources of Pt are limited inthe world. The use of Pt counter electrode greatly increases the cost of DSSC. Therefore, itis of great importance to explore Pt-free and considerably efficient materials to replace theconventional and expensive Pt counter electrode. As CoS has excellent electrocatalyticactivity, high electrical conductivity, abundant feedstock and low cost and graphene hasprominent conductivity, high specific surface area and feasible electrocatalytic activity, inthis thesis, we prepare the CoS-graphene composite counter electrode, and carry out ourresearch in the following areas:(1) CoS was prepared by hydrothermal method, then mixed with graphene, anorganic binder CMC-Na solution was added to form a paste, the resulting paste was coatedonto the cleaned FTO conductive glass by doctor-blade method. By changing the ratio ofCoS and graphene, preparing different counter electrodes;(2) XRD, FSEM, and EDS were used to characterize the structure and morphology ofthe CEs. The results show that the powders prepared by hydrothermal method is CoShexagonal structure, the particle size is rather uniform of about500nm, large particles areaggregated by dozens of nanometer grade small particles. For the composite CEs, CoSparticles are uniformly dispersed in the film, graphene is a curved layer structure, thethicknesses of these CEs are controlled to be13~15m, regardless of the ratio andelement distribution is quite uniform in the composite counter electrode film;(3) Electrocatalytic activity and long-term stability were carried out by CV. Theresults show that CoS has superior electrocatalytic property, the electrocatalytic ability ofgraphene is significantly improved when CoS is added to form composite counterelectrode. The electrocatalytic ability of the composite counter electrode is better than Ptcounter electrode and the long-term stability is as stable as Pt; (4) Photovoltaic performances were shown by I-V curves and EIS. The compositeexhibits excellent synergistic effect shown as much smaller charge-transfer resistance andNernst diffusion impedance. Power conversion efficiency (PCE) of the composite counterelectrode is better than CoS and graphene as counter electrode alone;(5) Finding out the optical ratio of CoS and graphene. As the ratio of CoS increases,Jscand FF increase first then decrease. Among all the CEs, DSSC with40wt%CoS and60wt%graphene as composite counter electrode achieves a maximum power conversionefficiency of6.31%, better than those with CoS (3.51%) and graphene (4.26%) electrodealone, and even better than the conventional Pt electrode of5.98%.