Study On Graphene-based Counter Electrode For Dye-Sensitized Solar Cells

State-of-the-art dye-sensitized solar cells (DSSCs) have triggered great attention due to their high conversion efficiency, ease of fabrication, low production costs, and environmental friendly nature. Typically, a DSSC device consists of a dye-adsorbed nanocrystalline TiO2 photoanode, triiodide/iodide (I3-/I-) electrolyte and counter electrode (CE). The CE plays a vital role in collecting electrons derived from conduction band of TiO2 photoanodes, and catalyzing the reduction of I3- to I-. Traditionally, noble metal Pt is extensively utilized as the ideal material for CE because of its extraordinary electrocatalytic ability. However, Pt is precious and its electrochemical stability in corrosive electrolyte is also unsatisfactory, which hinders the large-scale fabrication of DSSCs seriously. Thus, the exploration of low-cost and high-performance alternatives to Pt reference is urgently sought after.Various kinds and resources of carbon materials have been widely applied in energy storage and conversion field due to their extraordinary conductivity and good electrochemical stability, such as carbon black, fullerene, carbon nanotubes, carbon nanofibers and graphene. Graphene, a two-dimensional atomically thick carbon nanomaterial, has been tremendously popular owing to its unique physical and chemical properties. Phosphorus-doped graphene (PG) and nitrogen and phosphorus dual-doped graphene have been successfully synthesized in this work. Their performance for catalyzing the reduction of I3- as CEs in DSSCs have been investigated and the main content are as follows:PG was synthesized through thermal annealing process using GO and H3PO4 as C and P sources. The features of the two-dimensional structure of graphene are well maintained and the incorporation of P atom leads to more defects, which changes the electronic and chemical properties of G. The PG CE delivers a better electrocatalytic activity towards the reduction of I3- in comparison to that of commercial Pt and G CEs. The influences on the performance of PG result from different raw material ratio and annealing temperature were investigated, suggesting that a high conversion efficiency of 7.86% can be achieved when the mass ratio of GO and H3PO4 is 1:1 and the annealing temperature is 800?. The performance in supercapacitors was also studied to explore the potential as multi-functional catalysts.NPG was synthesized utilizing ball-milling process followed by thermal annealing approach employing melamine and triphenylphosphine as the N and P sources. The ball-milling process ensure the successful incorporation of N and P atoms into the G matrix, which results in lots of voids and defects. When applied as the CE for DSSCs, the NPG shows a remarkable catalytic activity compared with that of N-doped graphene (NG) and P-doped graphene (PG) due to the synergistic effect. The influence on NPG CE derived from different annealing temperature was investigated. The DSSCs assembled with NPG CE delivers a conversion efficiency of 8.57% and superior electrochemical stability when the annealing temperature is 900?.