Co_xS_y And Their Composite Materials Based On Graphene For Dye-sensitized Solar Cell

Dye-sensitized solar cells(DSSCs) have attracted many attention as emerging energy conversion devices due to their low production cost and relatively high conversion efficiency. As an important component in DSSCs, counter electrodes play an essential role in regulating device performance by electrocatalytically reducing the redox couples that are oxidized after dye regeneration. Platium is commonly used as counter electrode material due to its excellent electro catalytic activity. However, platium is expensive and rare on the earth, leading to a increased cost of DSSC. Hence, extensive studies have been conducted to explore alternative economic and high catalytic activity counter electrode materials.In recent years, cobalt sulfide has been used as counter electrode material in DSSCs due to its low cost and high catalytic activity for the reduction of I3ˉ. Nevertheless, the synthesis of cobalt sulfide materials requires expensive and toxic agents, as well as high reaction temperatures, and produces pungent H2 S from the sulfur sources. In addition, the low conductivity of cobalt sulfide is another factor to limit its large-scale application. Based on the above discussions, develop facile and environment-friendly method to produce cobalt sulfide materials, and combine cobalt sulfide with high conductive material to improve its conductivity are highly desirable. Thus,the major work is presented as follows:Three-dimensional flower-like cobalt sulfide(Co S) hierarchitectures have been prepared via a simple hydrothermal approach based on an organic molecule directing technology. The growth of the Co S nanostructure is described in detail and the performance of the dye-sensitized solar cell based on the Co S counter electrode is evaluated. Electrochemical measurements reveal that the flower-like Co S is a superior catalyst towards the reduction of triiodide( I3ˉ), which can be ascribed to the sheet-like structure is favorable for the diffusion of electrolye and the enhancement of specific surface area. When it is used as a counter electrode for dye-sensitized solar cells, the power conversion efficiency is comparable to the efficiency of the cell with a Pt counter electrode.In the current study,graphene wrapped Co S three-dimensional hierarchical porous spheres(CSHPS-G) are reported. A facile one-step hydrothermal method is used to synthesize such three-dimensional architecture. The electrochemistry performance of the RGO, Co S and CSHPS-G are all investigated. Compared with the single component material, the CSHPS-G composite has exhibited a higher electrocatalytic activity, which can be attributed to the RGO layer providing a robust electrical connection within the entire electrode framework and the apertures e xist in the electrode framework offered high accessible surface for electrochemical reaction and efficient diffusion channel for electrolyte. Consequently, the device based on CSHPS-G electrode showing a higher photovoltaic performance than that of the Pt electrode, which is resulted from the synergetic effect between Co S hierarchical architecture and RGO.Cobalt disulfide(Co S2)/reduced graphene oxide(RGO) composite(CSG) films has been prepared on FTO surface by combining layer by layer assembly method and thermal treatment. This method is not only avoid the process that mixing slurry of active particles, polymeric binder, and coating slurry on substrate, but only can control the thickness of film. More importantly, the CSG film obtained a small Rct and J0 in the electrochemical test, indicating that the CSG film has excellent catalytic activity for the reduction of I3ˉ. As a result the DSSC with CSG counter electrode exhibits comparable efficiency to the cell with Pt counter electrode.Cobalt sulfide/functionalized graphene composite(CFG) thin film has been obtained via a modified layer by layer assembly method based on the electrostatic interactions. As a result, without the aid of additional polyelectrolytes, the oppositely charged functionalized graphene and charged ions can be electrostatically assembled to form CFG thin films in an aqueous environment. The elecrochemistry test demonstrated that the CFG film has a good catalytic activity for the reduction of I3ˉ. Due to the good dispersion of Co S nanoparticle, which is facilitated by functional groups on graphene, the DSSC with this cobalt sulfide/functionalized graphene composite electrode generates comparable power conversion efficiency to that of the Pt electrode.